Coating a layer of gum Bichromate emulsion onto paper is the most important step
involved with gum printing. It is also probably the EASIEST!
You should coat your paper with emulsion indoors, usually a single tungsten
light bulb will suffice. Light bulbs do not emit much at all, if any ultraviolet
radiation.
My emulsions are left to dry in a dimly lit room and I have never
experienced any fogging, or exposure by ambient light. This is because the speed
of gum emulsion is so SLOW, it takes quite a lot of energy to start exposing.
For
this step you will need:
your mixing tray
your sponge brush and something to mix with (I use a cheap 1 inch brush)
some color choice of pigment or water color paint.
>> First, you need to pick your color choice of pigment
and squeeze a little "worm" of pigment into your tray. I am using Charcoal
Gray here.
I have found that in general, the less pigment you use, the
more transparent the layer will be, and the less likely staining will
occur. LESS is MORE!
Using transparency by using less pigment allows you to layer more and build up to your desired
tones
in while printing rather then hoping for the best in one shot.
>> Then you will add Equal Amounts of gum Arabic and
Ammonium Dichromate Solution so that the proportions are 50%-50%.
You can
measure it precisely if you wish, I just eyeball it. Getting the right
total amount just takes practice and experience.
>> Now take your mixing brush and stir it all together,
keeping most of the emulsion together to keep it from drying. Be
sure to squeeze your brush in a clean area to get any excess emulsion out
of it so you can use that emulsion too!
>> Next, get your sponge brush and load it up with
emulsion. You might use about half of the emulsion at first, but it's
perfectly fine to load your brush up again. Try to use as much as you can.
>> Begin coating your paper around the edges of the
intended image area. This helps you see the boundaries better as you are
coating. Or, if you prefer clean edges, you can mask off the edges with
painters tape. I prefer the lively messier edges myself.
The paper may or
may not feel very dry at first. If it does feel dry, you probably need a
little more gum and dichromate in your emulsion to make it wetter.
>> Continue coating in vertical and horizontal strokes,
keeping the layer looking as even as possible. There will always be light
and dark streaks from your brush. After a few passes, the emulsion should
appear fairly even. When printing multiple layers, these streaks will blend to create a subtle textural effect I personally find pleasing.
>> Finally, set your paper somewhere dark or dim to dry
for about an hour or two. A low speed fan to circulate the air helps. Most uneven streaks from your brush will tend to diffuse out onto the paper, although some will always stay.
Important!: Dichromate works by oxidizing the gum Arabic. This process
makes the gum Arabic insoluble to water allowing us to develop it in water. Oxygen in the air is also oxidizing gum prints just as it does to cut apples left in the open, or iron left in water.
This
oxidation begins happening once the emulsion is dry. Exposing the emulsion to ultra
violet light greatly accelerates this reaction. Normally you should try to
expose an emulsion within the same day or the next day after mixing it and coating a sheet of paper. After a few days or weeks
you will not be able to use the emulsion effectively as it has all oxidized and will not wash off the paper easily, if at all, during development.
