Mechanics of Gum Printing

Having talked about the more aesthetic aspect of gum printing it would be helpful for those anticipating gum printing to have a grasp of the procedural aspects of the medium. Controlling image over many layers of color additions is one aspect of the printing. Controlling how the image sits on the paper is another aspect. As I noted in an earlier article on the subject, the pre-shrinking and sizing of the paper is absolutely necessary, as there is a sort of handshake between the level of sizing, and the gum mixture itself that controls how the image sits on the supporting paper.

As noted, the sizing was 2 1/2% gelatin soaked into the paper for 30 seconds to one minute. Twice. That is a different outcome of just sizing the paper once with 5% sizing. The best match I've found to that sizing formula is a gum mixture of 50%. That would be roughly twice the thickness of the liquid 14 baume gum mixture sold on the market. Baume is the measure of viscosity, or thickness to a liquid heavier than water. Distilled water is 0 on the scale; said gum being 14. I know gum mixtures as a percentage being I mix my own gum liquid. At one time I was able to secure raw gum as beautifully clear chunks. Best gum Arabic possible. Now, that is only sold in palates or 100 Kilo bags. Enough raw gum to keep every gum printer in the world in gum for the rest of their lives.

I don't imagine any reader would need to ask how one arrives at a 50% mixture of gum, but, one never knows, so it goes like this. I use a pint sized clear plastic storage jar with plastic lid for this. Being that said gum will be purchased these days in powder form, the process is simplified from tying up raw gum in cloth then suspending it in water, to keep the sticks and twigs and other impurities from also getting to the finished gum mixture, to simply pouring the [distilled] water in the vessel before pouring in the measured gum powder.

100 ml Distilled water placed in a vessel with lid ~ 50g of powdered gum Arabic poured in and stirred until all the powdered gum is wetted. Put the lid on and let it sit for a day, usually, unless it's cold, which will take a bit longer.

100 ml worth of gum Arabic mixture will make probably six 8x10 gum prints, on average, and I multi coat each gum. I use two eyedropper draws of gum and two dichromate eyedropper draws for each coating for an 8x10 print. You will notice that the gum mixture will draw higher into the eyedropper than the thinner dichromate mixture. Lessening the dichromate retards printing sensitivity, hence the need for a longer print time to compensate. I eyeball the different levels and draw a bit more dichromate to add to the two, to make up for the differences. The vast majority of any gum print I do will have at least six layers, more likely 8-10 and some will get fifteen layers, perhaps some day reaching even more.

Also note that gum Arabic can 'spoil' as it is mostly used in the food industry as an additive, and it will  spoil. To keep this from happening, formalin is used. Formalin is a weak mixture of Formaldehyde. Formaldehyde generally comes at about a 37% solution, which is then reduced to a 10% solution; from Formaldehyde to Formalin. Use about 1 drop per 5ml of gum mixture as a preservative. It works quite well. The  final part of the procedural process is brushing the gum onto the paper. I have tried different brushes and found an artist's brush remains the best for smooth coating, no streaks. The problem being artist brushes start very small and reach about 1" or so wide. For an 8x10 print that is workable. I have used that for awhile now. But it does necessitate working swiftly before the gum becomes sticky and begins to streak.

What I have found, and used a couple times now, is an artist's "Dye" brush set. Cheap too, at around $8 for the set. Apparently a dye brush is definitely wider than most artist brushes and the bristles are not exactly taper cut as the artist brush but works admirably for this process. The larger of the two brushes is a good 2" wide and I am able to smoothly brush all the poured gum mixture out over the image area in less than 15 seconds. Plenty of time before the tackiness arrives.

Also note that a gum printer will want more than one brush in the tool kit. There is no rule that says the entire image area has to be coated each time. Nor is there any limit on the array of colors one can add to the print image each printing. Just because a single black and white negative is being used for the process, doesn't mean there is a limitation to the outcome of the print image. Advanced gum printing includes individual object coloring, sometimes with an tonal array of colors. The leaves in the trees in "The Quiet Pond" image were each colored by hand, with a very tiny artist's brush, using six color variations of yellow and green, respectively. Gum printing isn't just coating a print over and over.

Interested gum printers wanting to learn the art of this process will realize these articles are a primer on how this art form is more fully realized. The number of successful gum printers today, in the world, is a very small, esoteric group of individuals. To be able to continue this tradition of printing, one of the oldest known photographic process, about the age of salt paper printing, is to me a pilgrimage of sorts. Keeping an old and beautiful form of photographic art alive, and hopefully expanding upon the original applications. Simply google Edward Steichen gum prints to see where this process began, and where printers can take it today.