In order to make a gum print, you need to mix your own photographic
emulsion and coat it on paper. For this you will need various substances, and
tools which I will outline and describe to you here.
Here is a list of ALL of the
essential basic supplies I use to make Gum prints:
Most of these are easy to find, or you already own, and
they are all fairly inexpensive. I get my Gum Arabic and Ammonium Dichromate from Photographer's Formulary
Gum Arabic
Gum Arabic was once known as Gum Acacia and
its use dates back in history
about 5000 years. Basically the substance is tree sap from the Acacia Senegal
trees. The Ancient Egyptians were some of the first to use it for hieroglyphics
and mummification. It was introduced to Europe through Arabian ports and became
more commonly known as Gum Arabic. Today it is used in foods for fiber
supplements, candies, and all sorts of
things. Watercolor paint is pigment mixed with Gum Arabic for a binder. (I
do not recommend ingesting gum Arabic for use with photographic processes)
Gum Arabic looks like a gooey semi-transparent brown liquid.
You can also find it in a dry powder for mixing with water to the
consistency you wish. Photographer's Formulary sells Gum Arabic in Liquid form which works superb for Gum Printing.
The main attribute and MOST IMPORTANT property of Gum Arabic
that we will exploit in Gum printing is that Gum Arabic normally dissolves in water, even after it
dries. Alphonse Louis Poitevin realized in the mid 1800's that Gum Arabic
mixed with the chemical Ammonium Dichromate, when exposed to sunlight, would
become insoluble in proportion to the amount of light it received.
In simpler terms, where sunlight shines on the Gum Arabic /
ammonium dichromate mixture, the gum hardens and is no longer able to
dissolve in water. When you rinse a sheet of paper coated with the mixture
in water, normally it would all wash off in time. But after exposure to
sunlight it no longer washes off. With the use of negatives or objects to cast
shadows, you can control where the gum stays and does not. Any pigment
trapped in the gum will be permanently adhered to the paper, forever
recording the shadows you made.
Ammonium Dichromate was once called Ammonium Bichromate, but
for various naming conventions in chemistry the Bi prefix was updated to a
Di since the late 1800's when this process was developed. However, in
photographer slang, the term Bichromate is still widely used.
Ammonium Dichromate is a dangerous
substance!! (see the MSDS). It can
cause cancer with prolonged exposure. I get mine from Photographer's Formulary where it comes in crystalline form. The crystals themselves can explode when
exposed to heat like a flame. When burned, dichromate will expand, releasing
smoke and heat causing a chain reaction in any nearby dichromate. This is
sometimes used in volcano models for science projects, (but plain old baking
soda and vinegar is much safer). We will not be burning dichromate here,
just getting it wet.
I have only used Ammonium Dichromate, and for all purposes
it has suited me well. It is less sensitive to light then Potassium
Dichromate. Since Ammonium Dichromate exposes slightly slower, you can
achieve a lower contrast scale. Gum printing is a very short scale
photographic process, however this can be compensated for in a variety of
ways such as low contrast negatives or multiple printings.
To use the dichromate for gum printing, you have to dissolve
it in water and keep a Ammonium Dichromate solution around. I keep mine in 8
oz. cheap plastic shampoo bottle from Wal-Mart, marking it with a skull and
crossbones.
Water Color Paints and
Pigments
Water color paint in essence is really only pigment with a
little Gum Arabic mixed in as a binder (or a glue to hold the pigment
in place). Water is watercolor's medium, the vehicle which transports the
Gum Arabic-pigment mixture into place on paper. The little tubes of watercolor paint
you can find in any arts and crafts store work just fine for gum printing.
The more expensive brands contain a greater ratio of pigment to Gum Arabic
then the cheaper "student grade" varieties. I use Grumbacher water colors
basically because they are cheap and readily available and still do a wonderful
job.
Others prefer to buy pigment in bulk and mix their own gum Arabic / pigment
solution. The upside to this is you know exactly what ratios of pigment to gum you are using and you can be even more
consistent in your printing. You can also make your own personal colors, and
be able to make them again exactly if you desire.
Pigment is material crushed into a fine powder that is
insoluble to water. Usually pigments are from rocks, bones, ashes, metals?
Some synthetic pigments are out there as well. I have heard of pigments such
as crushed brick being used in gum printing, or even cigar ash. Most pigments are absolutely
stable and wont fade after thousands of years. When the paper of your image
finally crumbles to dust, your pigments will still be the same color they
were the day you made your print.
You will learn soon that some pigments have different
tactile and visual properties. Some colors of pigment are very transparent,
but not because they are diluted. Other pigments are thick and chalky. A
painting professor of mine once described some pigments as being watery and
clear, very thin veils of color washing over the bottom of a very wide dish.
Other pigments are more like thick and heavy concrete dumped into the same
dish, piling up on the side in a heavy opaque mass.
Some pigments have been blamed for staining paper. I have
often come across this with very fine pigments such as lamp black, made from
soot. It likes to get caught in the fibers of the paper, for good, and this
can be an annoyance if you do not desire the effect. However, it doesn't
always happen that way. If you have the mastery to choose when to stain your
paper or not, it would be good to find out what pigments stain and which do
not in your case. I cannot be too specific about which pigments will and won't
stain because it all depends on what pigments or paint YOU use, or the
paper, or the sizing , or development and so on...
For Color Separation Printing using Cyan, Magenta, Yellow, and
Black: I use Thalo Blue, Thalo Crimson, Cadmium Yellow Pale Hue, and
Charcoal
Gray, respectively, or sometimes even Lamp Black.
Watercolor Paper
The paper you choose is actually very important to the
process of gum printing. The paper affects the texture of the image, how
many layers you will be able to wash off, and the lifetime of your print.
Factors about your paper choice to think about are:
Size
Weight
Color
Texture
Tooth
Since I have been very much a poor college student, I always
tended to the cheap stuff and found a way for it to work for me. I use 11x15
inch Strathmore watercolor 140 lb cold press, which generally has suited me
well (and its about as cheap as one can get), although I think it could use a little better sizing sometimes. (Sizing,
in case you are unfamiliar with the term, does not refer to size in inches
or anything, but rather treating the paper initially so that it does not
absorb paints easily and stain your image.)
Now, I size my paper myself and it has proven wonders for
me, and eliminated any staining almost completely keeping the white of the paper
as bright as ever! The more light reflecting up off the paper means brighter
and clearer colors and values. Staining however, can be a vital tool in your box so
it might be good to use a paper that can stain if you want it to.
I use 11x15 inch paper because it comfortably holds a 8.5x11
transparency, which is the largest I can print here at home. The size of
paper also fits conveniently into my sink for development.
140 lb paper (or 300g/m2) is good enough to work for
multiple layers. This is the weight of the paper. the higher
the weight, the stiffer and thicker (and more expensive) the paper is. 90 lb
paper is a bit too flimsy and dries all wrinkly. I would prefer a heavier
paper then 140 lb, but it does work extremely well when sized. You want a
heavy paper because you will be re wetting the paper perhaps a dozen or more
times, but always at least once or twice. If you use a paper that turns into
mush, then your print will be nothing more then a soppy stained pile of
mush. (Are you are willing to be abstract? By all means go ahead)
There are toned papers around I am sure. It is not something
very attractive to me, I prefer to make all tones and colors myself during
printing.
The Strathmore paper that I use has a slightly bumpy
texture on the front. I use the smoother backside instead. The smoother
surface allows more fine detail to be held in the image, which depending on
what you want can be a good or bad thing. I started out using Somerset
printmaking paper, it worked great and I made my first amazing single and
multiple layered printings with it, but as I wanted more from my printing, I
needed something that Somerset could not offer.
Somerset is very finely rough, made for absorbing and
adhering inks for intaglio printing. This texture of the paper is sometimes referred to as the
paper's tooth. Its very hard to explain, but the grittier and finer the
tooth, the better it can hold on to the emulsion. A plastic sheet would have
little or no tooth, whereas fine sandpaper has way too much tooth. The
Strathmore paper which I use is very smooth on the backside, but has enough
tooth to work with. Determining the texture or tooth of the paper you need
depends solely on you and your preferences, and even the image itself.
Water
It might seem odd I go on here to describe water of all
things, but there are important factors about water which do make a
difference.
When mixing a Dichromate solution it is said you should use
distilled water. I find that to be completely unnecessary. I use plain old
tap water when mixing mine. If you were trying to be as consistent as
possible, it might help to know exactly what is in your dichromate
solution, and you never know what is in tap water. My tap water actually has
1 part per million of ammonia in it, and is relatively hard, containing many
minerals. Some cities put Fluoride in the water supply (I had excellent
teeth for years because I drank tons of Fluoride tap water as a kid)
The most important thing about water is in the development
stage of your image, and that is the temperature. As anyone who pays
attention in high school chemistry class should know, warmer temperatures
increase energy levels and chemical reactions can occur more rapidly. In Gum
print development, you are dissolving gum Arabic off of the paper into
water. the warmer the water, the faster this occurs. I used to use
absolutely hot water because I was using a really toothy paper at the time
and always over exposing the print. The hot water helped me wash away more
gum faster. Now I use slightly warm or room temperature water for
development. It slows the process down, and actually turns out to be "safer"
for details in my image.
Mixing Tray or Bowl
Painters have pallets to mix their colors, gum printers
should have a bowl or tray to mix their emulation in. I used a sheet of
glass for a brief while, mixing my emulsion in a little puddle in the
center. It was messy and a pain.
One night my girlfriend at the time made some friends and
I
spaghetti, and brought a few of those plastic microwavable containers to
hold the leftovers. A few days later I was musing to do some printing, and
found the container on the top of the trash. Perfect! I rinsed it off and
still use it today!
It works so well because in each of the four comers of the
tray there is a little valley which I use as a rough measuring device for my
emulsion. I pour a bit of ammonium dichromate in one corner, and the same
amount of gum Arabic in the opposite corner, and squeeze a "worm" of water
color paint in the center. Its marvelously easy to mix it all up right there
with a brush and rinses off in an instant. It is able to mix enough for 1 or
perhaps 2 different prints. I will still have the little tray when I'm 92 I
am sure.
Brushes
There is no right or wrong in anything to do with gum
printing. That goes for which brushes to use as well. For mixing the
emulsion I use an old furniture painting brush, I guess that's what it is.
It's small enough to mix with anyway, and squeezes out any emulsion easily.
For coating the emulsion on the paper I use a sponge brush
about 3" wide. It really helps to even the coating of gum on the paper for
an even exposure, and it fits in my square container very well. I sometimes
cut a tint bit of the corners off to give the brush a rounded edge that is
less likely to drag streaks into my emulsion layer.
I also use some ink brushes or watercolor brushes
occasionally during development, to brush away unwanted tones or for other
effects.
Sink or Development Tray
To make a gum print it is essential to have a place to
develop your print. Large Photo darkroom trays would be ideal. But, if you
are like me and have very little space, then you might have to settle for
the kitchen sink (ERRRKK!!)
I know, I know, the Kitchen sink is not
a very safe place to have dangerous cancer causing chemicals.
Perhaps I am
flirting with disaster here, but I am as careful as I can be, and rinse the
sink out afterwards. If you do use your sink, PLEASE take precautions not to
poison yourself or others with dichromate!!
Contact Printing Frame
When you expose your print, you need something to
hold your negative or transparency firmly against the emulsion,
otherwise you'll end up with a perfectly exposed blurry image. Some
people have custom made contact printing frames with latches and pins
and foam to hold everything in place. I have always used plain old
glass, tape, and those black office clamps.
I started out using cheap sheets of glass, which
works perfectly well. However, the thin glass had a tendency to break!
Now I have two 16" by 16" panels of thick glass taped together at
one side for a makeshift hinge. the glass is about 3/8" think or so,
with grounded edges, and it is by far sturdier and I haven't managed to
break it yet. It is the kind of glass you'd find on a glass table, or
furniture. I am not sure exactly where the glass came from or where I
could buy more. Someone found the glass I use at a garage sale for a
couple bucks.
The
Sun (and the Moon?)
Gum
printing has so many variables that affect the outcome of the image, it
is often jokingly said that even the phase of the moon
can get involved!
Thinking about that for a minute, it might be conceivable that if
you lived near the coast somewhere and your water quality was effected
by the tides somehow, then sure, the phase of the moon will be a
variable to think about (though I'm sure any of its effects could go
unnoticed to the most scrupulous of observers)
If you use that fiery thing in the sky we call the
sun to expose your prints, well then it certainly will alter the way
your image turns out, in big ways! The image to the right shows the sun
in 4 month intervals. You can clearly see its activity changing over
time. The light we see from the sun is pretty steady, however, UV and
x-ray radiations fluctuate over time.
In addition to the sun's weather patterns, we have
our own earthly weather patterns to worry about! Cloudy days, windy days, hazy
days, time of day, altitude, seasons, and the list goes on. If you do
print in the sun, you should live somewhere that's sunny a good portion
of the time, say like here in Texas during the summer. A general rule of
mine is: If you could get sunburned, or at least a tan, you can expose a print.
I gave up on the sun and now expose my prints using an ultraviolet exposure unit. It has
never failed me once, and I now can print all night if I wished,
something the Sun or the Moon won't let you get away with!
Gum Arabic was once known as Gum Acacia and
its use dates back in history
about 5000 years. Basically the substance is tree sap from the Acacia Senegal
trees. The Ancient Egyptians were some of the first to use it for hieroglyphics
and mummification. It was introduced to Europe through Arabian ports and became
more commonly known as Gum Arabic. Today it is used in foods for fiber
supplements, candies, and all sorts of
things. Watercolor paint is pigment mixed with Gum Arabic for a binder. (I
do not recommend ingesting gum Arabic for use with photographic processes)
Ammonium Dichromate was once called Ammonium Bichromate, but
for various naming conventions in chemistry the Bi prefix was updated to a
Di since the late 1800's when this process was developed. However, in
photographer slang, the term Bichromate is still widely used.
Water color paint in essence is really only pigment with a
little Gum Arabic mixed in as a binder (or a glue to hold the pigment
in place). Water is watercolor's medium, the vehicle which transports the
Gum Arabic-pigment mixture into place on paper. The little tubes of watercolor paint
you can find in any arts and crafts store work just fine for gum printing.
The more expensive brands contain a greater ratio of pigment to Gum Arabic
then the cheaper "student grade" varieties. I use Grumbacher water colors
basically because they are cheap and readily available and still do a wonderful
job.
I use 11x15 inch paper because it comfortably holds a 8.5x11
transparency, which is the largest I can print here at home. The size of
paper also fits conveniently into my sink for development.
Painters have pallets to mix their colors, gum printers
should have a bowl or tray to mix their emulation in. I used a sheet of
glass for a brief while, mixing my emulsion in a little puddle in the
center. It was messy and a pain.
There is no right or wrong in anything to do with gum
printing. That goes for which brushes to use as well. For mixing the
emulsion I use an old furniture painting brush, I guess that's what it is.
It's small enough to mix with anyway, and squeezes out any emulsion easily. 
To make a gum print it is essential to have a place to
develop your print. Large Photo darkroom trays would be ideal. But, if you
are like me and have very little space, then you might have to settle for
the kitchen sink (ERRRKK!!)
When you expose your print, you need something to
hold your negative or transparency firmly against the emulsion,
otherwise you'll end up with a perfectly exposed blurry image. Some
people have custom made contact printing frames with latches and pins
and foam to hold everything in place. I have always used plain old
glass, tape, and those black office clamps.
Gum
printing has so many variables that affect the outcome of the image, it
is often jokingly said that even the phase of the moon
can get involved!