Gumoil

This gumoil tutorial has been updated. Please click here for the updated version. Thanks for visiting!

Gumoil print on Arches Platine, 1:2.5 sensitizer solution, single pass (one and done) print, wiped clean at sink, cleared in sodium metabisulphite (printed area approx. 12"x16")

I have been working with the gumoil process for about two and a half years. I was introduced to it during an advanced alternative processes workshop in Santa Fe lead by my friend and go to mentor for all things alt pro, Christopher James. One of Christopher's assistants for the workshop was Cotton Miller, an MFA student at the time, and adjunct professor in the photography program at Lesley University's College of Art and Design. Christopher asked Cotton to teach one of the quick, pop-up style lessons we often get when everyone is settling into whatever they want to work on. I rarely miss one because they frequently introduce me to something I might not consider trying otherwise. Cotton has done some beautiful work in gumoil, and although his gumoil lesson was quick, he had me very intrigued. 

The process was developed by Karl Koenig in 1990. Unfortunately, Mr Koenig passed away in 2012. I would put together a little bio of his with information on how and why he came to develop the process, but The Photographers' Formulary has already done a beautiful job of that: http://www.gumoil.com/wp-content/uploads/Karl-Koenig-February2012NL.pdf Also, an artist statement by Mr Koenig can be found here: http://www.gumoil.com/koenig-bio/ His website contains many beautiful images of his gumoil and photogravure prints: http://www.gumoil.com

And of course, you can find more information in Christopher's third and latest edition of his book, The Book of Alternative Photographic Processes. The gumoil process discussion begins on page 546, and you will find one of my images on page 548. You will also find other gumoil processing options from other artists in the book. I don't think I've ever NOT used this book when working in an alternative process. I have all three editions of The Book, and it is truly indispensable. The latest edition is massive and packed with information on oodles of processes. You can buy it at Amazon: The Book of Alternative Photographic Processes, 3rd edition

My work with the process (and a bit of a disclaimer)

For more than a year now, I have debated whether or not to put this blog post together. When I first started working with the process, everything I did went wrong. Then it would work, slightly, then fall apart again. I even walked away from it for several months. Rather than pester Cotton every five minutes for help, I looked everywhere online for information and found next to nothing. There were quite a few board discussions, but no outline of a working method or any in-depth trouble shooting. I found several blog and website posts where an artist would discuss his or her initial foray into the process with the promise of more to come as things developed, then, nothing. Then, when things started to work for me, I considered why there was so little information being put out there, even by people who were clearly finding success. My method is the result of countless hours of trial and error and hundreds (and hundreds) of dollars in paper, paint, chemicals, tears, therapy…. It has been both a monster lurking in my basement darkroom (and the darker corners of my mind) and a beautiful, nearly tamed beast that suffers my attentions from time to time. After going through all of the ups and downs, ins and outs, working incredibly long hours, and investing some pretty big bucks in my efforts to get this thing to work for me, it's tough to just release it into the great wide world of the internet, where anyone, both deserving and perhaps not, can swoop in, and take it for themselves, free of the labor and the costs. To simply run with it. Free, free of the torment…. 

I can say with a laugh that I'm past that now. I think I understand why so many who have found success are keeping it to themselves, and I'm sorry for the betrayal, but my photogeekness has taken over, and I must share what I know. I also know that anyone who has come here seeking the help I was seeking but couldn't find, feels my pain. I just hope this helps rather than confuses you even more.

I would also like to add that this is simply how I do things, and there is no implication here that it is the only way. There seem to be as many working methods as there are artists, so if you've come across another way of making a gumoil print or simply a different way of completing one of the steps, keep in mind, different combinations work very differently. Try a few, and find what works best for you while creating your own path. 

The process, in brief

The gumoil process begins with a negative, usually colorless, gum bichromate print. This first layer acts as a resist to oil paint that is applied after the gum layer has dried and fully hardened. Excess paint is wiped off after being allowed to sit on the paper for several minutes. This leaves the hardened gum areas lighter than the areas where there was little to no gum and where the paint has been able to get into the paper. The print is soaked in warm water then either wiped clean and left as is or "etched" with bleach to clear away some of the gum and expose the paper underneath making another pass of paint possible. Each step of the process is always finished with a cool water running water bath to remove excess chemicals and to clear away unwanted gum or paint film.

The positive transparency

The gumoil process uses a positive transparency for the gum layer rather than a negative, so that what we end up with is a gum bichromate print in negative form. We want what will be the shadow areas in the final print to be clear of any gum resist and to be paper white in the gum print, so that when we apply our paint, it can stick to the paper in those areas. The areas containing hardened gum bichromate will resist paint, allowing the highlights and even some middle tones to be wiped clear. 

Because gum bichromate tends to have a very limited tonal range (around 6 stops), you need to squeeze your highlights and shadows into a small space. In other words, if you used a normal positive image for your transparency, with a normal tonal range from deepest black to whitest white, including subtle tones in those areas and in between, you would lose detail at one end or the other during exposure. If you exposed your gum print for enough time to get what will be the darkest visible details in your shadow areas to print, your highlight details will be overexposed, becoming washed out and showing no detail in the final print. The opposite is true if you expose for your highlights, so, you need to find a good middle ground. And, because a gumoil print will be getting wiped or bleach etched for clearing, it is very lossy in terms of detail. You need to focus on maintaining (exaggerating, really) your finer details while making your positive transparency if those details are important to you. Squeezing in the tonal range while holding on to detail contrast is tricky with this process.

I am no negative/positive-making-techie-aficionado, by any stretch of the imagination, and my methods for making these things are possibly a little sketchy. I keep meaning to knuckle down and learn a proper working method… Anyway, this is what has worked for me. Whether I’m making a print using multiple passes of paint and a bleach etch or I’m making a single pass, one and done (as I like to call them) print that gets one layer of paint and no bleach etch, I always start with a rather washed out, or “flat” image for my positive transparency. This flattening out of the image is a result of reining in the far ends of the tonal range, and generally speaking, what I START with for a gumoil transparency would work okay for my regular gum bichromate printing. Further editing and contrast will need to be done for gumoil though. Regular gum bichromate printing creates a thin layer, and the final print is usually built up using multiple layers. Since building up my gum layer in gumoil isn’t something I consider an option, I make one gum layer and rely upon it to give me a range of tones and contrast. I’ve found that while maintaining a compressed tonal range is crucial, it is also important to have good contrast throughout my gum layer to allow areas of clear paper to show through while other details of the image remain intact and thick enough to act as a resist to greater and lesser degrees to oil paint. Because of this, I add contrast back into my flattened out image using Shadows/Highlights, HDR Toning, and Levels sliders, and occasionally curves in my image adjustments in Photoshop. Each image is different and because of this, I start out with a fairly mild curve that doesn’t flatten out my image quite as much as a regular gum curve would. I go back and forth between flattening out the image and building it back up a couple of times so that I can maintain good control of my details and contrast.

For multiple pass prints, the quick, no frills way

Keeping the above information in mind, there are times when I’m not terribly concerned about detail loss and go ahead and print my positive using the first step only: I work in Photoshop using a black and white image that is fully edited to where I like it and I add my gumoil curve. This is one that I created and always start with. It is not an extreme curve, and the reason I like to use it is because it frequently works for multiple pass prints with little to no additional Photoshop adjustments. It’s simple, but because there has been no tweaking done to the shadow and highlight details, I know there will be losses. It’s just a way to get something quickly, and it’s best for multiple pass prints that can handle a little more exposure time than single pass prints. ALL of my single pass prints get further adjusting in Photoshop for tonal range and overall contrast. 

Simple gumoil curve

For single pass, one and done prints, the hard way 

For my one and done prints, again working in Photoshop, I start by creating a copy (or adjustment) layer of my background to use for making adjustments. I never make the adjustments to my original background image because I want to be able to compare it to what I’m doing, and to have it around in case I want to create new layers from it later on. My first adjustment is made using the Shadows/Highlights sliders. I do this before any other adjustments because it is a form of HDR Toning that wants to broaden and evenly distribute tonal range and contrast. I like to add that little boost in detail contrast before I flatten out the tonal range with my curve. I go to Image-Adjustment-Shadows/Highlights and make some very minor adjustments to both shadows and highlights. 2-4% for each is usually plenty right now, but with this process, I can push it a little further without worrying about odd HDR effects showing in my final print. At this point, I create a copy of this layer because I will likely want to do some tweaking and comparing with a couple of different versions. To apply my gumoil curve, I go to Image-Adjustments-Curves and select and apply my curve. Next, I go to Image-Adjustments and select Levels.

(Yep, I use Levels and not another Curves adjustment at this point in my fine tuning. Don’t know why, but it just worked out that way, and it works well for me. If you are more comfortable using the Input and Output controls in Curves, by all means, go that route.)

Since I'm going to be flattening out the image again in Levels, I pull the INPUT ends (shadows at one end and highlights at the other) back in a little to start out with a little contrast boost. Then, I take the little dropper that comes along with Levels and find a 50%(+/-) area in my image and make note of it. I want this to stay roughly where it is. I then find my darkest tone, or blackest black (usually at 99% at this point due to the curve) and make note of it. Then comes my darkest shadow detail that I want to be able to distinguish from the blackest black in my final print. Then comes the whitest white, then the lightest highlight detail that I want to distinguish from white in my final print. Using the sliders at both ends of the OUTPUT Levels, I start to lighten my shadow range and dim down my highlight range. I usually try to get my blackest black to around 90-95% (watch the percentages in the “info” tab and note the changes), my darkest shadow detail to around 80%, my middle tones roughly 48-54%, my lightest distinguishable highlight detail at around 20%, and my whitest white at about 0-5%. One or more of the sliders in the Input Levels usually need to be adjusted as well to keep my numbers where I want them. The default for Output Levels starts at 0 at the dark end and goes to 255 at the light end. I frequently have the dark end around 20(+/-) and the light end around 240(+/-). This can vary quite a bit sometimes, depending on the image I’m working with and what I want to get out of it, so think of this as a jumping off point and not something written in stone.

At this point, I add some contrast back in with with the Shadows/Highlights adjustment (usually 3-10 for shadows, 3-5 for highlights). This doesn’t work well with every image though, and I find that even the smallest amount of shadows/highlights adjusting at this point can make a change that’s too dramatic. Something I find myself doing these days is adding that boost of contrast with a little (very little) HDR Toning after I’ve gotten my positive to about where I think it needs to be. Even though this is done after applying my curve and reining in the ends of my tonal range, it can be done using very fine adjustments rather than the more automated and less refined Shadows/Highlights adjustment. (IMPORTANT NOTE: HDR toning also requires that you flatten your image. I don’t know if there is a way around this so that you can keep your background image and other layers intact.) 

I've found that doing this gradual, back and forth thing between flattening out the image then building detail contrast back in works well, and I never lose detail because I'm not making dramatic adjustments along the way.

An example of overdone HDR that works, if you like the look. This was an HDR iPhone image that I converted to black and white. It shows a lot of detail, but starts to look a little too much like a drawn illustration in areas with contrast.

Shadow details look fine, but...

...where there is contrast, there are weird outlines.

Multiple pass prints the hard way 

One and done prints seem to be the type I usually make these days, and I build my multiple pass prints off of what is working with them. I have two methods. The first is to take a positive that is working well for a one and done print and increase the contrast just a little bit. The slight increase in contrast works well with the increased exposure time (10-25% more) that will be needed because of the bleach etch that gets used for multiple pass prints. This method works best if I’m going be brave and go as far as a third, or even fourth pass. The second method is to leave my transparency as is and simply add a little more time to my exposure (10-15%). This method usually works well for just one additional pass of paint. The former method tends to yield cleaner prints with a little less of the visible grain that you get with gumoil, but the latter is quicker because the positive transparency is already printed and ready to go. I like the grain, but it really depends on the look I want. 

All of the above instructions are just jumping off points. I almost always have to go back in and make some fine adjustments to contrast after trying a print. I’ve gotten to where I treat each image differently, and the amount of contrast and detail I want and whether I’m making a one and done print or a multiple pass print can change the editing of my positive dramatically.

If you prefer a different workflow, here are a couple of examples to eyeball

I’m going to assume that there are people who want to work in a different way when creating their positives, so I’m including some pictures of my original images, their transparency versions, and the final prints. Hopefully, folks can emulate the look using their own workflows.

Original image

Positive transparency version

Final gumoil print on Arches Platine, 1:2.5 sensitizer solution, single pass, wiped clean at sink, cleared in sodium metabisulphite (printed area approx 11.5"x17.5")

Original image

Positive transparency version

Final gumoil print on Arches Platine, 1:2.5 sensitizer solution, single pass, wiped clean at sink, cleared in sodium metabisulphite (printed area approx 17.25"x11.5")

At this point, I’m ready to print my transparency. I go to Image-Image Rotation-Flip Horizontal so that when I place the printed side of my transparency in contact with the surface of my paper, it will print in the proper orientation. I use a Canon iPF5000 that does not need any ink output adjusting. It’s pretty close to WYSIWYG in terms of going from screen to transparency. Often, any further adjustments to what I want to see in my highlight and shadow details can be made by adjusting my exposure time, but sometimes, it’s back to the old drawing board.

The sensitized emulsion (sensitizer) 

Potassium dichromate solution

The sensitizer used for the gum bichromate (also called gum dichromate) layer is a mixture of saturated potassium dichromate solution and gum arabic. This is also what one uses when making a gum bichromate print, but the ratio of dichromate to gum is different, and there is typically no pigment added for gumoil. Many gummists consider a 13% solution of potassium dichromate to be saturated, but I use a pre-mixed solution from Bostick and Sullivan that is a 10% mixture. It's what they sell specifically for gum printing and works quite well. Potassium dichromate is nasty stuff. It is considered carcinogenic and mutagenic, among other things. Use caution with this chemical. Keep it off your skin, out of your eyes and mouth, and do not breath it in either in powder form or in mist form if you are spritzing your prints to clear excess hardened gum. If you are mixing the dichromate yourself from a powder, to make a 13% solution, add 13 grams of potassium dichromate powder to every 100ml distilled water. A  10% solution would be 10g in 100ml distilled water, and so on. 

Ratio makes a difference in the sensitizer

The ratio of dichromate to gum that I was taught to use is what Koenig used--1 part potassium dichromate to 3 parts gum arabic. This is what I used for the first several months that I worked with the process. I had mixed results that were far from predictable, but a lot of that unpredictability might have come from my own inconsistency in all of the variables that exist in this process. In any case, after many losses and few gains, I shelved my work with gumoil for several months. It was the gains that brought me back. The magic of seeing a print come to life after a rinse is very exciting, so I decided to give it another chance. Right from the start, things just fell into place. There was consistency, predictability, and I was happy. One day I realized that the 1:2 solution (dichromate:gum) I was using wasn't what I was supposed to be using. I don't know how I ended up using a 1:2 solution rather than the 1:3, but wrong was right for me. I now typically use a 1:2.5 solution. This is what works best with the Arches Platine that I use most often, but I've found that thicker, more fibrous or velvety papers yield better prints with the traditional 1:3 solution. The 1:3 solution is thicker and tends to flake off in larger bits when I use it on Arches Platine, but the velvety papers hold onto it better. With less dichromate, the 1:3 is also slightly less light sensitive, and this is something to take into consideration when switching papers and ratios. I seem to need 10-15% more exposure time when using a 1:3 sensitizer mixture.

The gum layer

The first layer of the gumoil process is made using the gum bichromate solution described above. A positive transparency (NOT a negative) is used during exposure utilizing either sunlight or a UV exposure unit. During exposure, the gum bichromate hardens to greater and lesser degrees, depending on the density of the areas within the positive transparency. The unhardened gum is washed away in the first rinse following exposure.

When coating your paper, you want a smooth finish without any obvious brush strokes or gaps that allow plain paper to show through. The amount of thickness also needs to be uniform. If the coating is too thick, it will tend to flake off in the rinse. Applying it too thinly can result in a coating that is not uniform, leaving paper exposed where you don't want it to be. Though, if you do it well, you can get a nice effect with a creative brush application of the gum bichromate.

Brushes

I use Richeson synthetic flat wash brushes for almost all of my alternative process coating. They hold liquid nicely, clean up better than a lot of cheaper brushes, leave a fine, smooth coating, hold up well over time, and don't leave debris in my coating. I quarantine them--no using the same brush for different processes. If you're going to use the sponge type of brush that Koenig is shown using in his YouTube video, get good ones. The cheaper ones have larger bubbles/holes, and tend to feel more plastic-y. The better ones are made of denser foam, feel soft to the touch, and those bubbles/holes are much tinier. The denser foam brushes create a smoother finish than the cheap ones, and tend to leave less debris in the gum layer. I feel that foam brushes leave too many bubbles in my coating, especially two or three sheets in, and when they start to wear out, they all leave little bits of themselves behind. They don't hold up well to multiple uses, so you'll be throwing them away rather frequently, and they soak up a lot of your sensitizer. They are considerably less expensive than the Richeson brushes up front though, so if you're just looking to get your feet wet with the process, you might want to start with the foam. Get the widest brush you can for your sheet. For prints that are in the 11x17 range, I use a 3" brush. This helps keep the coating smooth and even. 

Coating the paper

Mix enough solution ahead of time to cover all of your prints with a little left over. As much as I hate wasting solution, having extra is always better than trying to spread a thin layer over a sheet of paper just to find it's not enough--wasting paper is even worse. Before coating, I lay my transparency on top of my paper and make little marks in the corners that are about 3/4" larger than the actual printed area of the transparency. The reason for this large border is that the edges of the gum layer tend to develop an uneven texture from the brush. It's best to have this well outside the print area to avoid flaking off in thicker spots. To cover 3, 11"x17" print areas on Arches Platine (not the paper size, but the size of my transparency plus a little extra), I mix 10ml potassium dichromate to 25ml gum arabic (1:2.5) making 35ml of solution. Using my watercolor brush, I get full coverage for those three sheets with just a little left over. If you're using a foam brush, you will have to mix more because the brush soaks up a lot of the solution. Some papers that have a little more surface texture, like the Rives BFK that I also frequently use, need more sensitizer to cover well.

Before applying your sensitizer, dampen your brush in distilled water then gently press out the excess with a paper towel. When loading the brush with sensitizer, I make sure it is full but not dripping when I go to the paper. I apply the sensitizer at a corner first, brushing along a border, heading toward another corner. Then another corner and border, and filling in the center as I go. This helps keep the borders neat, especially on larger prints. After I get all the solution I will need on the paper, I start to smooth it out, working quickly. I work one direction at a time: all strokes left to right, then top to bottom, then right to left, then bottom to top. Smooth, steady, even strokes. I keep going until I feel the gum starting to tug at the brush. If I go too long, the brush starts to skip across the gum, and this leaves marks in the coating that can show in the final print. If you find little bits of pet hair, brush fibers or sponge debris in the solution on your paper, remove it before the gum gets too dry and brush to smooth out any marks you made. If your coating is too tacky to remove the debris, leave it until after the coating is dry and carefully try to remove it before exposure. (wear gloves! even dry, this stuff still has active dichromate in it!!) If you can't get it out, then go ahead and expose anyway, but know that it might leave an open area in the paper and that area will take paint. I try to put these little bits of debris into the darker areas of the print so they won't show. 

Let the coated paper dry completely

After the paper is coated and the surface has started to go from shiny to matte, it is hung to dry in a dark, dry space. The paper will have a crispness to it when it's dry, and it won't have cool spots on the back where the moisture is still evaporating. In my (relatively dry) basement, it usually takes about 3 hours to dry, but I still hit the backs of each sheet with a hair dryer for 2-3 minutes (larger prints) just to make sure they are completely dry. If there are any damp areas in the paper, the sensitizer won't expose evenly, so drier is better. Some folks keep their gum coated paper in a dry, dark place for a few days, but I don't like leaving mine unused for more than 10 hours or so. 

Lighting in your workspace

Though gum bichromate isn't very light-sensitive until it is dry, use safelights or yellow "twinkle" lights (LED christmas lights) when coating and whenever handling your freshly sensitized paper to err on the side of caution. I use Philips Hue lightbulbs. I can change the color and brightness of my lights using an app--very convenient! Once your exposed paper is in the water, you can turn the white lights on.

Exposing 

For exposure, I use a UV unit that was designed for screen printing. It is an aluminum box with the lights below, and a sheet of glass above. The paper I'm going to expose is placed face down on the glass with a negative or positive transparency in between. I use either a contact print frame or compression (sheet of plexiglass with weights on top) to keep the transparency in firm contact with the paper. The 36"x36" exposure area on this unit is great for large prints. UV units give you a boost in predictability that working with the sun does not afford, but yes, they can be expensive. There are plenty of DIY instructions online for building one, so you might want to look into making one for yourself.

Many of my prints these days are single pass, one and done prints. My exposures with a 1:2.5 solution, my type of transparency, and Arches Platine take between 4 and 6 minutes for a one and done print. Rives BFK off-white takes just a smidge more time than the Platine, and if I use a 1:3 solution, it will take a little longer still. Using a 1:2.5 solution with Stonehenge Rising takes 10-15% more time than the Platine. Unfortunately, there is no way for me to describe what your gum layer should look like immediately after exposing because a very wide range of exposures will give you fully realized negative images before washing and clearing the print. What it looks like after clearing is what's most important. The areas that will be your darkest blacks should be paper white or very nearly so. You should be able to see your darkest shadow details in faint relief when looking at the paper from different angles if not straight on. You should be able to see definition in the denser areas of the wet print as well (what will be your highlights). Before developing a better positive transparency working method, I used to expose my gum print to where it was just about to lose it's highlight detail. Using this method, I didn't always get shadow detail I wanted, so again, getting the positive transparency right is crucial. Doing test strips helps considerably. 

Things to consider when adjusting the gum layer for a second pass (layer) of paint

The above paragraph is describing what I do for single pass, one and done, prints--one layer of paint and no more. I don't typically attempt a multiple pass print until after I've gotten a good single pass print working. After I've got a good single pass print, I start working from it to get a multiple pass print. When making multiple pass prints, I will be etching the gum to open up areas of paper to let in more paint. This etching means I'll need more exposure time and/or more contrast in my positive transparency to give the gum bichromate a little more thickness. Some prints will only be getting one additional pass of paint and only need a little extra exposure time to allow for the etching. A 10-15% increase often works well for this type of print. Sometimes I'm just adding one light pass of paint and can get away with using the same exposure time I would for a single pass version. Etching can do a lot of damage very quickly though and can be difficult to judge. Shooting for a second pass with a single pass exposure often yields a much grainier image as well. For prints getting more than two additional passes of paint, I will slightly increase the contrast in my positive and add 10-25% more exposure time to allow for multiple bleach etchings. Every time you etch, it's a bit unpredictable and becomes increasingly more so with each subsequent etch. I've rarely gotten a truly successful fourth pass of paint, and even the third passes I've done were often a dicey business at best. You might also want to try using a 1:3 sensitizer ratio with an even longer exposure for multiple passes. This ratio creates a softer gum layer, and you might find you like it more for bleach etching and multiple passes. I find it to be more unstable and less predictable though. A change from 1:2.5 solution to a 1:3, for 2 or more passes, could easily go to 25% more exposure time, if not more.

Paint block-up with long exposures

One very strange phenomenon I came across early on was having large areas of my print "block-up" with oil paint despite the fact that I could clearly see gum in areas that weren't releasing the paint, and I knew that I had given the exposure a lot of time (8-10 minutes). The paint just wouldn't wipe off where it had done so in many other prints. So, you would think the logical response would be to expose longer, right? Huh-uh. A longer exposure only made it worse. In an angry fit, I even let one go for something like 15 or 16 minutes to just completely gum up the entire surface, and it raged right back at me by completely blocking up with paint--none of it wiped clean! I found at least one other tortured soul in an online discussion board seeking help when he or she had the same problem. I have no idea why exposing the gum for too long would cause it to stop acting as a resist to the oil paint, but it seems you can do just that if your exposures are way too long. 

Clearing the gum bichromate negative print

After exposure, the print will be a negative and will have gold to medium-dark brown areas in it. Don't fall in love with it. It will change A LOT after rinsing. First, it gets a soak in very warm to hot tap water (not so hot that you couldn't keep your hand down in it) for 10 minutes. Sorry, I know the lack of exact temps here will drive some people nuts, but unlike film developing, it doesn't seem to make much difference as long as the water is at least very warm. After the 10 minute soak, I give it a gentle, warm water spray with my hose end sprayer at my sink. (Note: wet gum bichromate has a sort of mushy thickness to it that rinses off in tiny bits, so as you can imagine, the little details of your image can get lost in this mushiness and in the clearing stage. It also stands to reason that bigger prints yield greater detail. If detail is important to you, print as large as you can to get the greatest detail.) Koenig used a spritz bottle to get bits of gum bichromate out of those small detail areas to open up the paper and allow oil paint to get in. I've never had success with a spritz bottle because it always removed too much gum bichromate and did so unevenly. I turn the water pressure way down when using my hose end sprayer so it doesn't create a mist the way a spritz bottle does, and I'm not worried about breathing in dichromate particles. Consider your situation carefully, and act accordingly. The print is then washed in a cool running water bath for 30 minutes, and very gently sprayed once again, this time with cool water, before hanging to dry for a few hours. At this point, the print is but a faint version of its former self. It will be a very pale, sort of olive-gray-green color. Be sure to observe the print at different angles to the light while it's wet and look for the detail in what will be your final print shadow areas. Has it washed away? If so, increase your exposure time or rework your positive transparency. Have the areas that will be your highlights become blocked up, showing little detail or contrast? This might still print well if you're doing some etching and multiple passes, but if you want a single pass print, you might have to shorten your exposure time or rework your positive transparency.

DO NOT LEAVE YOUR PAPER IN ANY OF THE CLEARING OR WASHING TRAYS FOR TOO LONG. You can end up leaving your gum layer in the rinse for too long and lose too much gum. You might still get a decent single pass print from it, but you may not get the opportunity to do any etching if too much of your gum washed away while you were clearing it with water.

The paper

Arches Platine is a beautiful paper, and it's my go-to paper for many alternative processes. It has a very slightly velvety surface and holds up very well in water, even after multiple passes through trays of chemicals, coats of paint and dichromate, rinsing, repeat, repeat, etc. It also tends to shrink less than most papers, making any registration easier. It's just a very good paper. I also use Stonehenge Rising paper, but the 320gsm (120lb?) version is getting harder to come by in anything smaller than 30"x44". The Stonehenge has a harder size in it, and because of this, the gum layer needs about 10-15% more exposure time than the Platine for the same end result. Rives BFK (280gsm) is a traditional printmaking paper, and it feels similar to the Platine before wetting, but the fibers are raised considerably after wetting. After the gum layer is processed, the paper will have a little more texture to it than with the Platine. This means that the paper will hold more paint though, so the blacks are richer, and colors more intense but usually at the expense of finer detail. Just a slight difference, but if you're picky about detail, consider adding just a little more exposure time for this paper if you're going from Arches Platine to it. I use the off-white, and like it a lot as an alternative to the bright white of the Platine. The buff color BFK seems like a completely different paper and didn't work well at all when I tried it. I've also used Twinrocker watercolor paper with some success. Lastly, if you use the back side of the Platine, it works a lot like the smooth side of the BFK off-white and holds onto the paint more. It does have a different texture than the front, and I waver back and forth about it.

In brief:

Favorite paper is Arches Platine. Smoother finish, finer detail, but slightly lighter black, paler colors, backside yields deeper black but has different texture and might yield less detail. Less shrinkage than with most other papers I’ve tried.

2nd favorite is Rives BFK 280gsm off-white. Deeper black, colors more intense, but small details can get lost, and paper shows more texture. Also needs slightly longer exposure.

3rd favorite is Stonehenge Rising 320gsm. Finer detail, but blacks and colors are a little lighter. Only available in very large size. 

The paint (not all paints are created equal…)

A good place to start with gumoil is a rich, deep, black. Lamp black fits this description better than any others that I know of. There are artist grade paints and student or economy paints. Always buy the former. Student and economy paints are cheap for good reason: they don't hold up well and colors often are not permanent. As a painter, I tend to use good quality, artist oil paints. Though I'm not really a fan of Winsor and Newton paints, I started doing gumoil with a Winsor and Newton lamp black because it was available in a large tube, and hey, it's a carbon based black that won't fade, regardless of who makes it. And yellowing? You only have to worry about that with light colors, right? Eventually, I moved on to a lamp black by Williamsburg which is a better quality. I was also using my favorite Gamblin paints for the colors. Loved them a lot. 

Then, this happened…

This past Thanksgiving, my husband and I took some gumoil prints to his mom's house to show her what we'd been working on. I had just spent a couple of months making several prints and taking careful notes for this gumoil tutorial blog post, and was feeling excited about posting. That was until I pulled out some of my older prints. Many were yellowing badly wherever the paint was. Even the ones I had just made were starting to show some very pale yellowing. I had never noticed it. The older the print, the uglier the yellowing. It was bleeding through the backs of some of the prints in the shapes of the images on the front, and the yellowing was also bleeding out from the paint areas into the front of the paper. This was true of the prints made with the Winsor and Newton artist paints and both the Williamsburg and Gamblin artist paints. I was gutted. 

Back of a print that is roughly 2 1/2 years old and has badly yellowed linseed oil on it.

The good news

After some research and some paint testing, I am convinced it was the linseed oil in the paints I was using. Although both Williamsburg and Gamblin use what they call refined linseed oil (very common practice) that is less likely to yellow than lower quality linseed oil, the oils they use were still turning yellow after soaking into the paper I'd made my gumoils with. The Winsor and Newton and Williamsburg were much worse than the Gamblin but still caused too much visible yellowing for my taste. After some more research and testing, I now use M Graham oil paints made with walnut oil for my gumoil printing. These paints are wonderful, and none are yellowing on me well over a month after having been applied to paper. Even if they do show some yellowing later on, it should be minimal. There are paints made with safflower and poppy seed oils that apparently do little to no yellowing as well, and may do so even less than the walnut oil based paints. They are more expensive though, and this process eats a lot of paint, so paint cost is something you might need to consider. Sennelier Extra-Fine Artist Oil Paints are closest in price to the M Graham, and I will probably try these after my current supply of M Graham blacks gets used up. Maimeri Puro is made with safflower and poppy seed oils, but they are more than double the cost of the M Graham.

Colors

Lamp black is a great black, but not all paint makers make it. Ivory and mars blacks are also nice blacks, a little lighter in tonality, perhaps, but good. As far as colors are concerned, check manufacturers' websites for the lightfastness of each color; it can vary considerable with less stable pigments. Reds can be tough in terms of stability. Stay away from alizarin crimson altogether. It just doesn't have a great lightfastness coming from any brand. There are also differences in the transparency of paints. Opaques tend to have less oil (lean paints) and transparents tend to have more oil (fat). Transparent paints are frequently very high chroma (intense color), and the combination of a lot of oil and a lot of color can mean staining, even in areas where you don't want it. Manufacturers usually state on their websites whether their individual colors are opaque, transparent, or somewhere in between.

Oil-based etching inks and water mixable-oil etching inks and paints

The oil-based etching inks that I tried were a no-go. They were too hard to rub on and impossible to wipe off. After that experience, I didn't even try the water-mixable etching inks I have, but I did try a water-mixable oil paint. It was interesting and might be worth looking into further at some point. Initially, the dry print wiped cleaner than the ones made with oil-based paints tend to, but as expected, the paint started to wash away once the print was put into a tray of water, and further attempts at wiping highlight areas after the paint and paper were wet just made them muddy and messy. Next time, I think I'll try wiping areas clean with a damp sponge or soft cloth after the initial excess paint wiping is done. This would likely leave me with no option for a second pass of paint though, but it would certainly cut down on the mess in my darkroom sink. I might not have an opportunity to clear highlights with sodium metabisulphite either, so a thinner gum layer might be in order. Perhaps after having an opportunity to dry, these water-mixable oil paints might become less likely to wash away in a rinse, and clearing the highlights in sodium metabisulphite might be an option. 

Paint application

Prepping your paint

After your gum bichromate negative print has dried completely, it's time to apply the paint. I make sure the paper is dry by blow drying it for 30 seconds or so. (NOTE: A strange thing happened recently. I forgot to blow dry one of three prints one day, and it came out darker than the other two. Although this could be due to some other processing anomaly, I can't help but wonder if it's like taking a damp cloth to wood before staining which helps raise the grain, allowing the wood to absorb the stain better. Just a thought.) If you're starting with a mixed color, make sure you have mixed enough ahead of time to cover the entire area you intend to use it in. You might not be able to mix the exact color halfway through the application, leaving you with an uneven color application. If you're going with an unmixed black or other paint that doesn't need mixing, just squeeze out as much as you think you'll need. If any excess oil comes out of the tube along with the pigment, soak it up with a paper towel--don't mix it in. You want as little oil in the paper as possible. If there is still some oil around the paint that you can't soak up, don't worry about it but do mix it in before you grab some and start applying it to your paper. I use a paper palette pad, and I cover any leftover paint with plastic wrap to keep it from setting up for as long as possible.

Tape down the gum print

I like to tape off the edges of my print before adding paint to keep it neat and clean. If I wanted to be really neat and uniform, I would also be taping the paper before applying the gum bichromate, but I haven't gotten that picky yet. I use a very low tack tape that I get through amazon that is made by Protapes or Pro Scenic: Pro Scenic Tape. It is sold as a painter's tape and has gotten mixed reviews for use in that way because it doesn't stick as well as some DIYers would like, but it's perfect for this purpose. It is far less likely to damage my paper than any other tape I've tried, and I feel it would make a great all around artist's masking tape, if not for the color. 3M also makes a white low tack paper "labeling" tape that I believe uses the same type of adhesive as their Post-it notes pads but is more expensive than the purple tape I use. I tape right up to the edges of my print border and right out onto my table. This also keeps the paper steady for me as I wipe paint on and off of my print. Remove the tape before processing at the sink.

Brush, or cloth?

I started out using stippling or stencil brushes for paint application. It's a good way to get a lot of paint onto the paper rather quickly. One technique is to sort of stab at the paper with the loaded brush to get the paint into the paper fibers. I've found that with a good gum layer, I don't need to do this. I now use a lint-free cloth for paint application that I purchase through Tap Plastics: lint free cloths. I cut each sheet into quarters, and gently, but firmly, rub the paint onto the paper. I have more control this way than when using a brush. I also waste less paint, and I don't have to worry about cleaning brushes, which is messy and tends to waste a lot of rags and/or paper towels. 

Wiping paint off again 

I leave the paint on the paper for 15-20 minutes before wiping it off. I use Viva towels for wiping the paint off. They are old school paper towels that resemble workshop towels. They are more felt-like and less like something that might look good as a bed coverlet in larger form. No fancy quilting, patterns, colors or anything with these towels. They absorb the paint nicely, and hold up to the tacky nature of what's left of the paint on the surface of your paper. I fold them over twice, and keep unfolding and refolding to keep the clean areas ready for use. I wipe until I can see the details in my image (it will be a positive at this point) and there is just a faint hint of paint still showing up on my paper towel after wiping. There will be a gray (or whatever color you choose to start with) haze over everything. You can wipe too hard and for too long though. If you find that your shadow areas are getting too light, then you are either wiping too aggressively, or you need to rework your positive or shorten your gum exposure time.

Taped down print that has had the excess paint wiped off

At this point, you can leave the paint on the paper for a little while. I would think an hour or so wouldn't do any permanent damage, but if you wait too long to clear the gray haze of excess paint out of your highlights, it can start to stick and stain.

Processing the print after applying paint

Start with a brief soak 

Whether you're going for a single pass, one and done print or doing multiple passes, your print now goes into a warm water bath. Leave it face down for 3-5 minutes, making certain there are no bubbles trapped under the paper. You will likely see some of the paint lifting off the paper and floating around in your tray at this stage, which is normal. After soaking, I rinse my prints with a gentle spray from the hose end sprayer at my sink to remove some of the loose paint. 

To etch, or not to etch

It was funny seeing some of the conversations in online forums between the (bleach) etchers and the non-etchers. The etchers couldn't understand how the non-etchers could get any sort of print without using bleach to clear away some of the gum and paint, and the non-etchers couldn't understand how anyone could use bleach because for them, it always removed too much, if not all, of their images. Some were frustrated and angry, and lot of them were like me--lost and just all over the place. Again, there was no clear instruction either way, so I fumbled through a lot of trial and error until I had decent results with both. You don't need to bleach etch to get a great print, but I almost always etch if I'm going to do more than one pass, or layer, of paint.

Single pass, one and done, print

After the 3-5 minute soak in warm water and a gentle spray, I place my print on a sheet of plexi that is sitting in my sink and leaning against a wall. I then gently wipe the print with either a soft cloth or sponge, alternating directions and gently rinsing the print with my hose sprayer and warm water. (NOTE: I do not wipe a print at this stage if it is going to be bleach etched) The print then goes into a sodium metabisulphite bath to clear the highlights. The concentration I use is .75%, or 45 grams in 6 liters of water. A 1% solution is what many gummists use for clearing (10g sodium metabisulphite/liter of water), but it can be pretty strong and might loosen up too much of the gum, allowing some of the paint to wash away where you don't want it to. I leave my prints in this clearing bath for 2 to 4 minutes, agitating from time to time and checking to see if my image is holding. You should see the color of the gum bichromate in your highlights change from a slightly warm tone to a lighter, cooler one. After removing my print from this clearing bath, I put it back onto the plexi, and rinse it with my hose sprayer with warm water, gently wiping areas to clear them a little more. Cotton balls and Q-tips work nicely. If you find that you are losing too much of your image at this point but liked the way it looked before it went into the sodium metabisulphite clearing bath, then forgo the clearing next time if you're okay with the dichromate color in your highlights. I'm not a fan of it myself. I have yet to lose anything I don't want to in my clearing bath. If the positive, the sensitizer ratio, and the exposure are working properly, loss of image in the clearing bath is never a problem for me. In fact, I can't even remember it ever happening to me, unless I've done a bleach etch first. 

If you are losing too much of your image after wiping but before the clearing bath, then try a shorter exposure time. If this yields shadows that are blocked up and lacking detail, then rework your positive and either brighten your shadow details or darken your highlight details to bring the two ends of your extremes closer together. Remember, too wide a range in tonal scale does not work well with gum bichromate or gumoil. If your print starts out too dark, then go the other route--try a longer exposure. If you lose highlight detail, again, rein in the tonal range of your positive. 

Here are a few examples of my one and done prints, all on Arches Platine, using a 1:2.5 sensitizer ratio, wiped clean at the sink, and cleared in sodium metabisulphite. All printed areas are approximately 11.5"x17.5":

Adding color to a one and done print

After the print has dried, if you like, you can wipe on a thin layer or oil paint, but remove it quickly. After disturbing the gum layer by wiping it, it has gained some texture and no longer works the way it would if you were going to etch your print to clear some of the paint and gum. The paint wants to stick even where gum is still present, so I tend to wipe it off as I'm wiping it on. I don't put the print back into water again because too much of the paint comes off in some areas while sticking badly to others, creating an unattractive texture. Instead, to clear some highlight areas, I use a damp cloth or Q-tips. To be honest, I'm usually not too fond of what I get if I add oil paint after wiping my wet print clean at the sink (one and done). I do like to add color with oil-based color pencils though. No special techniques here, just add color like a kid with crayons and a coloring book. I haven't tried watercolor with a "one and done" print yet but have used them effectively after the etching process.

One of my single pass, no etch prints that has been colored with oil based pencils

And, there is always that exception:

This is a single pass print that got a bleach etch but no second pass of paint.

Single pass print on Arches Platine, 1:2 sensitizer ratio (note the ratio) that was etched in a 1:6 (note that ratio as well) bleach etch for a count of 8 mississippis then washed. (printed area is approx. 12"x16")

Multiple pass print using a bleach etch

IMPORTANT NOTE: I do not wipe my print after soaking as I would for a single pass, one and done print. I feel it removes too much of the gum and paint before putting it into the etching bath. This etching method also yields less fine detail in my experience, which can be either a good thing or a bad thing, depending on what you want. Bleach etching can allow you to create a beautiful stark look if done well. 

After wiping the excess paint off the dry print at my work table, I remove my tape and place the print into a tray of warm water to soak for 3-5 minutes making sure there are no bubbles trapped underneath, then give it a gentle spray with my hose sprayer. After the soak in warm water, I place the print into an etching bath that is a 1:8 solution of household chlorine bleach and tap water--1 part bleach to 8 parts water. In a 16x20 inch tray, I usually use 500ml of bleach and 4 liters of water. The bleach acts very quickly, and I count seconds in my head the absolutely nontechnical way (a metronome would be better): one-mississippi, two-mississippi, etc, for 12 to 16 seconds, then put it into fresh, cool water. I take my print out of the bleach before I'm finished counting to let it drain off a bit then try to get it into the fresh water as I'm counting that last second. When dealing with such short amounts of time, every second counts, so don't hold your print over the bleach tray after you have finished counting just to let it drain off. The bleach is still eating away at your gum layer while you're doing this. You also don't want to carry a lot of the bleach with your print into your tray of fresh water. If you have room for a second tray of fresh water, move your print from the first tray of fresh water and into the second after several seconds to further dilute any residual bleach. 

Etching time is crucial but difficult to get right

Although the standard time for the first etch is 12-16 seconds, the time you need really depends on everything you have done to this point--the tonal range of your positive, the sensitizer ratio, how thickly (or thinly) you've applied the sensitizer, your exposure time, how long you left your gum layer in the rinse, etc, etc, etc. If you etch for too long, a lot of your detail washes away. And I'm not just talking about bits of paint, as this happens normally after an etch, but rather, the gum itself. With too much of the gum gone, there is no hope of any further detail. Any time you etch, you will simply lose SOME of the fine detail, never to return. This is one of the inherent traits of the process that I am drawn to--the contrasty, grainy nature of gumoil that is a result of a print that has been etched and had a second pass of paint applied. 

Clear and hang to dry

A minute or so after placing my print in fresh water, I move it to a cool, running water wash for 30 minutes to clear the bleach from the print. When it's time to remove it, the gum is very fragile, so I don't disturb it with a spray from my hose sprayer, and I don't brush or touch it in any way. I will, however, let the water from an open hose at my sink run very gently and smoothly across the surface of the print while it's still in the tray, then hang it to dry. You can get a similar effect by gently washing water over the print with your hand to clear away any stubborn gum or oil paint film, being careful not to splash too harshly. 

Another trick for gently clearing away some stubborn bits after you have etched your print and it has come out of the final rinse is to hang it by a corner for a couple of minutes, rotating it once to keep the surface evenly wet, then place it back into the water. For some reason, letting air get to the surface tends to open it up, and more of the gum and paint film washes away after it is placed back into the water. If you overdo it, you can lose too much gum, and subsequently, more detail. 

I hang the print to dry and look carefully at what is going on at this point. There is always a thin film or haze of paint left in my highlights while some of the darker mid tone areas have gotten lighter and grainier. These darker mid tones were the thinnest areas in the gum, and they have been etched to where the paper is now clear enough of the gum resist to allow paint to get into it for the next pass. I don't try to clear the highlights of the hazy paint film yet because it is only temporary, and the gum is too fragile anyway. Disturbing it too much at this point usually spells disaster for me. Those hazy, lighter areas are where I want some resist left on the paper.

Applying a second pass of paint

After the first etch has opened up the darker end of the mid tone areas in the paper and the print has dried, it is ready for the second pass of paint. If I'm creating a black and white print, I'll simply mix a little titanium white (less chalky and slower drying than zinc) into the same black paint I used for my first pass to make a very dark grey. I've never liked the look of an actual middle grey at this point. It appears muddy to me. This second pass of dark grey can also tone down the grainy look that is so prominent in gumoil prints. It fills in some of the gaps, creating a slightly smoother look. It can be applied to isolated areas or over the entire first pass. If my print is already looking fairly finished but I want a color for atmosphere, I will apply it to either the whole print or just isolated areas. Creating a print with a range of colors can be done at this point as well, but things can get smeary and muddy very quickly if care isn't taken to keep colors separated, especially when wiping the excess paint off. It takes practice. I use blending stumps, Q-tips, and bits of cloth to apply paint if I'm coloring finer detail.

After applying the second pass of paint, I usually leave it on the paper for 15 to 20 minutes (less for really intense colors), then wipe off the excess. If I've applied more than one color, I'm careful not to smear them into areas where I don't want them. I work quickly to avoid color staining, but neatly as well. 

If I'm cheating a little and want to use a print that would have worked as a one and done single pass print (no wiping at the sink, of course) then I would shorten my etch time by a few seconds because this type of print doesn't typically have a long enough exposure for multiple passes of paint. Sometimes it works, sometimes it doesn't.

A one and done type of print that I etched a little too briefly (6 one-mississippis) before adding a second pass of paint. I kind of like the washed out look, though the bricks on the building went a bit pink.

Another one and done type that got the proper etching time, allowing paint to get into the paper, but the highlights are a little muddy and show a lot of grain. A longer exposure time for my gum layer would have likely yielded a cleaner look.

If your print looked fine after your first etch (if slightly reduced because some loose paint washed away) but gets blocked up with paint in the second pass, then you have etched too long for the type of print you have created to this point. If you didn't etch your first pass long enough, there will be little change in what you see after your second pass of paint than you saw after the first. If this happens, you can always try another etch, but keep it much, much shorter than the first if you still want to try another pass of paint. Half as much time, if not less. 

Etching (or not) the second pass

After wiping excess paint off my dry print, I place it into a tray of warm water to loosen the paint and gum. I leave it face down, making sure there are no bubbles trapped underneath for 3-5 minutes. After soaking, I flip the print over and rinse it gently with my hose end sprayer with warm water, checking to see if any bits of paint are coming off. If the paint is coming off without an etch and I don't plan on trying a third pass of paint, I will use cotton balls and Q-tips to carefully wipe paint from the highlights. If the paint is not coming off with a gentle spray, and I'm still not looking to do a third pass of paint, then I will place my print into a 1:8 etching bath (again, 1 part bleach to 8 parts tap water) for several seconds. This second etch is usually shorter than the first, and 8-10 seconds is what frequently works. After the second etch, I place the print into a tray of fresh, cool water, then into the final wash of cool water. While it is in the final wash, I'll start to clear the highlights with Q-tips and cotton balls, being careful not to remove too much paint as I go. If I'm feeling very brave (or very stupid) and decide I'm going to attempt a third pass of paint, I will do a brief etch (8-10 seconds) but I won't wipe or touch or at all. I just move on as I would when going from my first etch to my second pass. I treat that gum with kid gloves, and reduce my etching time for each subsequent etch. Whether I have etched the print at this stage or not, it washes for 30 minutes before being hung to dry. 

Multiple pass print, 1:3 sensitizer ratio, lamp black paint, etched for 16 seconds, cadmium orange, etched for 16 seconds and light areas wiped clean. (printed area is approx. 7.5"x11.5"--small print)

Same as above, but I believe the color is prussian blue

Getting a starker look

This approach is the most painterly one and shows the artist's hand more than the others. You are only limited (well, mostly) by your imagination here. You can gently brush your print after the first etch if you want to get rid of detail. The tools you use are also up to you--stiff, soft, textured, smooth, etc. The etching time depends on the look you want, but starting at less than the standard 12-15 seconds is best. You can always pop your print back into the bleach for a second or two if you're not seeing enough paint come off with brushing. Clearing in cool running water afterward for 30 minutes is the same as the other methods. You can either leave the print as it is after gently brushing, clearing, and allowing it to dry, or add more paint. If there is no gum resist left on the paper (this can be difficult, even impossible to see), use a light color or apply deeper colors selectively. Applying deeper color all over a print that has no gum resist left on it will simply block up it up with paint. Sometimes you can get away with a light scrubbing to clear away areas after paint has been applied, but this really depends on how tough your paper is and whether or not there is still a hint of gum left on it. Stonehenge Rising seems to hold up better than the Arches Platine to this scrubbing, but the Arches does fairly well too. Watercolor washes work well too. If you still aren't getting the stark look you want, consider making a positive transparency with more contrast or using a 1:3 sensitizer ratio with a slightly longer exposure time. A 1:3 sensitizer is softer and less light-sensitive than a 1:2.5 but tends to brush off easier. 

Multiple pass print on Stonehenge Rising, 1:3 sensitizer ratio, bleach etched after first pass of paint, then wiped and scrubbed to clear some areas and leave others dark. (approx. printed area is 16"x20")

Something completely different

Gumoil over cyanotype works quite nicely...

That's all folks

For now, anyway. I hope you have found something useful in this rather lengthy blog post. I've tried to break things down with little headers to act as shortcuts for people who are troubleshooting or simply looking for a particular step in the process.

Notable artists

Lastly, here is a short list of artists working in gumoil for reference and inspiration: Cotton Miller and Michele Rogers Pritzl here in the US. Anna Ostanina in Russia. Karena Goldfinch in Australia.