Seth Troutner got so into making gum, he even made his own gum kit – to help beginners getting started. Here he shows how he makes his prints.
Chose the paper
Gum prints require that you use a substantial paper that will stand up to repeat soaks in water. Prints can be made with only one coat of emulsion, but most of the time you will find that multiple coats are necessary and with each coat the paper has to be soaked in water. If the paper you are using is not sturdy enough you will end up with a soggy mess. I have tried using several papers and have found that 140# pure cotton watercolor art paper works best for my needs. Pure cotton papers can be very expensive, but well worth the cost; if you are just starting out you will probably want to start with a less expensive artist grade watercolor paper that you can buy at any art supply store. The less expensive papers will work just fine for gum prints and are recommended for someone wishing to experiment with the process. As you get more experience you will find that the cotton fiber papers offer better control over the emulsion and how it develops on the paper.
Shrink the paper
Most likely the paper will have to be soaked in water more than one time and with each soak the paper will shrink or distort slightly. This will cause you register problems between coatings and the image will start to blur or get muddy. To avoid this problem you can Pre-Shrink the paper by soaking it in extremely hot water for a short period and allowing it to dry. The hot water will cause the paper to shrink to its nominal size before any emulsion is applied to the sheet. I personally use an old automatic coffee pot that I keep in my workshop to heat up water for shrinking the paper. You may find that some papers will have to be shrunk more than one time and only experience will tell how a specific paper will react.
Sizing the paper
Sizing the paper simply helps seal the surface of the paper so that the chemicals and color pigments will not stain the paper. You can make decent prints without sizing the paper, but you will find that it is very difficult to clear the highlights because of staining deep into the fibers of the paper. I have made several successful gum prints without using any sizing at all, but getting the proper amount of watercolor pigment was critical. Sizing the paper will give you more latitude pertaining to how much pigment you can add to the emulsion before it stains the paper and darkens your print.
There are many different ways to size a sheet of paper, but I don’t have a lot of experience in this area. The most common sizing consists of applying a Knox Gelatin solution to the paper before the emulsion is applied. There are several sites on the internet which explain this process in detail, but unfortunately I personally have no experience with the gelatin process; click here for some useful information on sizing paper. For my prints I like to use Acrylic Spray which I find much easier to apply because it dries in minutes. I purchase Acrylic Matte aerosol spray from my local art store and a single can will size many prints. I will caution that the spray can be a little temperamental due to the fact that if too much is applied to the paper it will cause the emulsion to fall off the sheet while developing; too little and the paper will stain. If you choose to use acrylic spray sizing I would recommend that you do several test prints to figure out how much spray is necessary. I have found that I get best results if I spray the sheet just enough to coat the paper, but not so much that it leaves a shine on the paper. If you can see shiny spots on the paper then emulsion is probably not going to stay in place.
There is no one right way to make a gum print, but there are wrong ways which can cause personal harm. Dichromate chemicals are dangerous and should be handled with care. Each person should make themselves familiar with proper handling procedures. The chemical can be fatal if ingested and will cause eye and skin irritation on contact. Excess amounts of ammonium dichromate should not be flushed to the sewer. It is recommended that you initially wash prints in a tray of water that can be reused over and again. Store this “first rinse” water in an air-tight container and continue to use until the water is dark brown and will no longer properly function. Dispose of as recommended by your local waste management commission. Only the “first rinse” produces high concentrations and secondary rinse water solutions can be disposed of to the sewer.
Mixing the emulsion
Image above right: Accurate measurement of chemistry will allow you to improve the formula to achieve the best print possible.
The emulsion is the most sensitive part of making a gum print. You should prepare the emulsion in a dimly lit room and should be stored in complete darkness. The emulsion is made by mixing water, gum arabic, ammonium or potassium dichromate, and watercolor pigment. There are dozens of formulas on the internet that will give you a good working emulsion. Each formula will require different techniques and each will give a different look to the finished print. The only way you will know what formula you like to work with is by experimentation. I am listing here the most common formula that I use to give a general idea of how the process works. The ratios can easily be adjusted for your personal preference.
First I prepare the gum mixture: 0.5 ounce (by weight) of gum arabic powder is added to 45 ml of hot water. Stir the mixture until it becomes a uniform brown syrup like liquid. This mixture should be a nearly saturated solution so I strain the solution through a piece of cheese cloth to remove any lumps that might be there. Store liquid gum in an air tight container and place in refrigerator for up to a week. If the mixture gets grainy over time add a tiny amount of warm water and stir.
Next I prepare the dichromate solution: Mix 0.5 ounce (by weight) of ammonium dichromate to 50 ml of warm water. Stir until all crystals are dissolved. You may also use potassium dichromate, but the ratio will be different and is not listed here. Store dichromates in light safe air tight container and dispose of liquid mixture after 72 hours (this is my personal experience). If crystals form in the solution you can warm the container slightly by holding in your hand and stir until crystals re-dissolve.
Prepare the Emulsion: I mix equal amounts of liquid gum and liquid dichromate solutions in a small container. I like to use a tablespoon (disposable) to measure out the mixture. My formula uses 2Tbl gum to 2Tbl dichromate in a small bowl and then mix to make the emulsion base. This amount is generally enough to cover a 9×12 piece of paper two times. Do not expose this mixture to bright light.
Add Pigment to the Emulsion: The pigment can be any color of watercolor paint that you choose. Some pigment colors work much better than others and black is the obvious choice for first timers. I would recommend using a high quality artist grade water color that comes in small tubes. The amount of pigment that you add to the emulsion is critical and there is no easy way to measure. For most pigment colors I add a small pea size amount to the 4 tablespoons of emulsion, but some colors require a bit more or less and only experience will tell what works for you. Mix the color thoroughly into solution. A little pigment goes a long way and if you are having trouble getting the emulsion to rinse away from the paper then you probably are adding too much pigment.
Apply emulsion to paper
Brushing the emulsion onto the paper requires a little practice. If the emulsion is brushed on too thick it will require longer exposure and can cause flaking when it is rinsed. Heavy brush marks will show up in the final print, but this is sometimes a desired look. If you do not want brush marks then the emulsion needs to be brushed on as smooth and evenly as possible. I like to use a soft brush to apply the emulsion to the paper and then I quickly brush with a much larger and softer brush to smooth out the finish. The gum mixture starts drying quickly so you have only a few minutes to get the desired finish. If you continue to brush after the emulsions starts to set up it will cause spots in the finish so work fast. Let the sheet air dry for about 20 minutes. A hair dryer can be used to speed up the drying process if you use low heat. High heat will damage the emulsion.
If you are an avid photographer you may already have the ability to make full size negatives, but the majority of us do not. Because of digital technology it is becoming very difficult to get full size negatives to make contact prints. There are services out there that can produce large negatives on image setters if you are willing to pay the price. If you are doing a multi-color print and require color separations the cost can be well over $100 for 8×10 negatives which is way too much for most hobbyists. There are other options.
If you have access to an inkjet printer you can easily print your own negatives onto transparency sheets. You must first either scan your photo or import a digital file into editing software that has the ability to reverse or invert the image so that it is a negative. Print the photo onto a transparency and you have your negative! The one big downside of this method is the cost of inkjet transparencies and ink (negatives use lots of ink).
If you plan on making multi color prints than you will need some method of separating out the colors. I have experimented with CMYK separations, but RGB separations have become my favorite. If you don’t understand what these terms means http://en.wikipedia.org/wiki/CMYK_color_model should help give you a little insight.
To make the different color negatives I use Photoshop to separate the Red, Green, and Blue channels on my computer. The channels print as follows:
- Red Channel = Cyan Watercolor
- Green Channel = Magenta Watercolor
- Blue Channel = Yellow Watercolor
My preferred way to make a negative is oiled paper. The process involves using a regular sheet of paper with the image printed onto it in reverse as described above. To make the paper transparent to light you wipe the paper down with vegetable or baby oil. This process makes the image slightly more contrast, but I prefer the look.
Exposing the image
The negative needs to be tightly pressed against the emulsion surface to get a detailed image. Two plates of thick glass with the emulsion/negative sandwiched in-between works very well, but a vacuum frame is best. The printed surface of the negative should be face down in contact with the emulsion for best results. If you plan on making more than one burn you will need to place the negative in exactly the same position each time. If you have trouble seeing the previous image through the negative I would recommend making pin holes in the four corners that can be easily re-positioned with thumb tacks over a cork board and then taped in place.
The UV exposure time of a print will vary greatly depending a multitude of conditions. The only way you can figure out the exact exposure for the density you are trying to achieve is through trial and error. If you are using sunshine to expose your print it will take a lot of approximation as to how long to leave it out. A high noon exposure will be much different then a late afternoon exposure and the only way to know is to try it. 10-20 minutes under bright sun is a good starting point.
I prefer to use a more controlled UV source such as a mercury halide lamp. The exposures are easy to calculate and repeat (and it works on cloudy days too). For my lamp I use a 9-12 minute exposure depending on which color I am printing.
There are a lot of variables when it comes to exposure times and I would recommend exposing test strips to see just how long you can expose a particular emulsion and still get the highlights to clear in a reasonable amount of time. Keep your test strips and write down the exposure times for future reference. I have found that even the same formula requires different exposures for different colors of pigment. You will eventually find your favorite colors and develop preferences.
One of the benefits of working with gum is that the print can be developed with just pure and simple water. I have tried several techniques of developing my prints and each one will offer a different look to the final piece. The one thing to remember is that when the emulsions wet it is fragile and very easy to damage.
There are many rinsing techniques such as wet brushing, pouring or streaming water, etc., but I would recommend just a soak in warm water until you are comfortable with how delicate the emulsion really is. I like to use room temperature water for the first soak to remove the majority of the dichromates which rinse away and turn the water yellow. After about 10 minutes in the first bath I move the print to a second bath of moderately warm water. In the warm water I gently agitate the print until all of the highlights are clear.
It is very difficult to get a good gum print with just one coat of emulsion. Most prints will require two or more coats and with each coat you risk damage of the previous layer. When brushing on additional coats of emulsion be sure to brush lightly. Aggressive brushing can damage the layer underneath even though it has been exposed and dried.
I still have difficulty understanding the theory behind the additive and subtractive process of blending colors using RGB and CMYK and the only way I have found success is by trial and error. When I experiment with a new watercolor pigment I usually will make a test print with layers of several different colors to visually see how they blend. Some colors do not blend well and create a dark muddy pigment no matter how thick or thin they are applied to the paper.
Variations and errors
Note: some of the grain in the following photos was caused by the poor quality of my scanner.
This photo of the barn was an experimental print that I made with CMYK separations printed as a tri-color. On my computer I mixed the Black channel equally into the C,M,and Y channels and output only the CMY negatives. Wherever the three colors overlapped in the shadow areas it would give the appearance of black. This is the same concept that RGB uses to create black, but when I was printing with Red, Green, and Blue channels (CMY watercolor pigments) I would get a muddy brown color instead of black. In this photo the use of CMYK channels did produce darker blacks, but obviously the bright colors were altered as well. My solution was to stick with RGB, but use darker pigments.
This is a photo of my stepdaughter that was printed CMYK color. The light spotty areas are the result of using too much acrylic sizing. This was an experimental print on which I used a very different formula and technique. Instead of just letting the print soak during the development, I used a paint brush to wipe away the unexposed emulsion in the bath of water. The formula that I usually used would just wipe clear away with the aggressive developing, so I had to use a much less saturated solution of gum by adding more water to the gum solution. The mix was very watery which made for a very thin emulsion. The thin emulsion had a short density range which required many layers to build up any detail at all.
This photo of the flower is another attempt at using a paint brush during development to clear the unexposed emulsion. The formula was again very watered down so that the emulsion was thin and many coats were used. This method makes for a very low detail high contrast print.
The gum print below is a sample of a bad emulsion formula. This is a 4 layer CMYK print using all for channels. The small white spots are actually clear areas where the emulsion flaked off the paper. I have researched a few theories as to why this happens, but I believe that in this case it was the amount of gum in my mix. I was attempting to get a more viscous emulsion by reducing the amount of water and increasing the gum arabic. The first two layers went down successfully and then the flaking started during the third rinse.
10 thoughts on “Gum printing basics – how to make a gum print (Troutner)”
Just a side note.
Potassium dichromate can be eliminated with sodium bisulfate. About 20 grams for a quart 13% potassium dichromate.
Years ago when I was working with dichromate chemicals I did not realize how dangerous they were. The warnings were added later. Always wear a mask when working with the dry mix. Always wear gloves when handeling it in dry or liquid form. The chemical ratios I posted here were experimental and near saturated solutions which are not necessary. Some artist use ratios lower than five percent. Dichromate liquid solutions can be stored for long periods if done properly. Thank you to everyone that has shared!
I am just beginning with gum printings and I have some questions.
I find VERY difficult to get a uniform coating when using the mixture gum-pigment-dichromate.
It seems easier to coat uniformly with gum and pigment alone, while adding the dichromate it seems that the mixture flocculates in dark small clots.
I tried the technique of coating with gum and pigment alone, let it dry and then sensibilize with dichromate solution, as commonly used in carbon printing, but again the coat flocculates, almost immediately.
By reading old publications (1850-1900) on gum printing a very uniform commercial paper is mentioned, the “Artigue” one, that was said to be developed in hot water, at least in the first version.
May be the base was gelatin instead of arabic gum?
Thank for your attention.
Great article, well written.
I have only a question: how many photo can we stamp using 45 ml of gum mixture and 50ml of dichromate solution?
thanks in advance
please send process or method of (TO MAKING OF ARABIC GUM SOLUTION) OR How to make arabic gum to used offset printing machine.
This a good article, but I really have to ask WHY you would throw away the dichromate solution after 72 hours? Dichromates mixed only with _distilled_ water last almost forever using the standard “store in a dark bottle and in a dry cool place” photo chemical mantra. This just seems insanely wasteful.
.5 ounces is about 14.2 grams which, in the 50 ml water the article is suggesting, is roughly a saturated solution or 29% (29 grams ammonium dichromate in 100ml of water). For potassium dichromate a saturated solution is about 13%, or 13 grams in 100 ml of water, which can be scaled accordingly. I should probably mention that many people don’t use a saturated solution and some folks use Potassium dichromate solutions as low as a 5% (maybe lower) and I personally use 10%.
This is so great! I was in South America and saw a man who was selling his prints but they were all done on canvas or watercolor paper. He’s also had alot of success using wood. I’d rather work with potassium dichromate. Do you know anyone who has a good emulsion ratio for this?
Seth, have ever tried mixing techniques, for eg: Albumen print with the gum process?
Thank you for breaking down the process so well in this article. Very well written, informative.
I have found that if I mask the outside edge of frame I get a neater edge, also when I apply the emulsion I use a plastic salad spoon to dollop the emulsion onto the centre of the paper. I use Schoellershammer Linen 225 gsm & 300 gsm, it handles my abuse of it’s surface quite well.
My paper is often stretched on to large oak tabletops which I bough at an auction when I was a student 25 years ago. I use brown packing tape, the type that you wet and apply.
I use a glass rod to spread the emulsion smoothly and evenly. If I want a more randon feel I then use a sponge or wall paper emulsion brushes, there is r4eally no limit to application techniques in my personal experience.
Once developed I coat the surface with a acrylic glaze which allows me to work over the layer with another exposure or work onto the surface with airbrush, sponges, brushes, even tint the surface with coffee which is much like chinese inks, by laying on layer by layer you can increase the density of the colour. I can erase some portions of the surface with a fibreglass rubber, the type that is used by architects beforte the days of CD and computers. I bought out the old stocks from local supply stores at one of their sales decades ago.
I also use a flatbed laminator, to flatten the surface and cure the image. If my flatbed is too small I then use an old steam iron.
I work very large too, because I work in a newspaper as a senior sub editor and photographer, I have access to very negative printers, and they are capable of one metre or larger continous film negatives.
As I use my own profiles I can control the neg outputs very accurately. All my negs are punched and pinned at the newspaper so that I can emulate the registration process at my home studio.
I expose using mecury vapour lamps even though we have an abundance of good clean and reliable sunlight in South Africa.
Once I have completed the image I either either photograph it or have it scanned using a large drum scanner. The digital image is then output digital once I have colour corrected and tweached the image through photoshop.
AS I do limited prints for boardrooms or family portarits I find the potasium dichromate allowsme an edge against my competiton and gives me a unique product at the end of the day.
I started this process mostly for editorial and annual reports when I worked as a commerical illustrator early in my working carreer.
I am now re-visiting the process as a fine artist and finding the process a huge amount of fun. The advantage of working so much bigger than the average is so that I can scan the image, reduce the image and finally when I output limited prints my images have a tighter grain with an even finish.
I often work on the edges of the images and my use of pigments span, water colours, gouche and acrylics, inks and house hold coffee and herbal teas.
For me the potassium dichromate image generates a base image which allows me to functions as a illustrator and fine artist.
Our process is similar but our output results ulitmately is different.
Thanks for posting this tutorial, it is very helpful. So, when printing with multi-colors, you coat, expose, wash, and repeat? Or do you layer the three coats of pigment on top of each other and expose them all in a row?