In the Previous sections we created Custom Photoshop curve to
compress the values of a digital image into a scale suitable for gum printing.
We tested 3 different exposure times and combined information from each test to
create an Average Scale which we used to make the Curve. The resulting Average
Curve is still a slightly longer scale then you could print with any one gum
printing, yet it is customized to your personal setup allowing you to use the scale in a
predictable fashion.
There are 2 ways to print this average
scale
>> The first and easy way is to print the scale at the middle
exposure time. For example, my times in the previous tutorial were 4 minutes, 8 mins, and 12 mins. You could expose your gum bichromate print for 8 minutes
every time and get a great result. A slight bit of shadow detail will be lost
and a slight bit of highlight detail will be lost, but nothing too drastic, as would have happened before you made your curve.
>> The second way works best and is what this average negative
scale was created specifically for. It involves printing at least two layers of
gum bichromate on top of one another in separate printings, one at a short
exposure time and one at a long exposure time. This is a printing process known
as a Duotone. The short exposure lets you print in only the shadows, and the longer
exposure time allows you to print into the high tones. Of course, I will demonstrate the
process below.
The Gum print to the right was made with a red in the medium tones,
blue in the darker tones, cyan in the highest tones, and was punctuated
with a dark gray or black in the darkest shadows. Combining tonal layers
by varied exposure times helps to achieve a full and rich photographic scale.
A
duotone is a printing process where the lower tones of an image and the
higher tones of an image are printed separately to enhance the detail of
tones in the shadows and the highlights. The image below illustrates the
principle rather clearly.
Light tones
+
Dark Tones
=
Composite
As you can see, we use a dark color for the dark tones and a thin, more transparent color for the light tones. In this example the dark tones of the dog are printed twice, once in a dark pigment, and again in a gray pigment. The addition of a gray pigment to the black pigment barley affects the dark tones of the dog, whereas the addition of the gray pigment to a white area, like in the sunlight, has a much greater effect in bringing out the details, resulting in a rich tonal scale when the two layers are combined.
Gum printing is a versatile medium allowing us to print as many layers or colors as we choose. You might use an orange rather then a gray for the lighter tones, the image will become warmer (or cooler with a blue instead of orange). You might even print 3 layers: 2 colors, and a dark gray for the shadows. The possibilities are virtually endless.
Step Two: Printing A Duotone
Printing a Duotone is a very straight forward process,
so you should have no trouble at all. It just takes a while. For this
example, I am going to make a straight forward gray and black duotone.
>> Decide which tone you will print first, the light
tone, or the dark tone. Generally, I start with the dark tones and add
in the lighter tones as I go, but not always. If I printed a thin yellow
over black for example, the thin yellow would turn the blacks a slight
green color, so in that case I would print the yellow light tones first,
then the dark tones last. It all is up to you.
Sorry images coming soon
>> In this example we are printing two shades of the
same color, black. For black pigment, I normally use charcoal gray which
really is a deep dark gray color. Normally when mixing an emulsion I
squeeze out a tiny little worm of water color, as illustrated in the Coating an Emulsion Layer section.
How much pigment you should use comes from experience and your own
working methods. I use very little pigment, normally only a 1/4 to 1/8
of an inch worm of pigment. I call this measure a "dot" of pigment. For
the dark toned areas I am going to use 2 dots of pigment, and for
the lighter areas only 1 dot of pigment.
>> Since we are printing the darker tones first in this
example, squeeze out 2 dots of pigment, mix your emulsion normally and
coat it onto a prepared sheet of paper.
It should look pretty dark on the surface of the paper, but maybe a
little transparent. Let the emulsion dry. Get Your inkjet transparency
of the photograph you wish to print, (which you made using the Average
Scale Curve from the last section)
and place it over the dried emulsion under glass.
Since we are printing the darkest image tones with this
layer, you will want to print the lower part of our average scale. We do
this by underexposing the layer using our minimum exposure time from our
previous scale tests.
My minimum exposure time was 4
minutes, so I expose this dark tone layer for only 4 minutes. In
some cases you might even expose for half of your minimum exposure time,
2 mins, to really punch in the darkest shadows. I did
this in the Alleyway Men Gum print shown above.
>> When you develop this dark tones layer, almost
immediately pigment will start to wash of the print. You will see parts
of your image appear before you, and then watch them get lighter and
lighter. Develop the print as you normally would, even though it appears
that most of the image is falling off!
Let it soak for the full time as
in your previous tests. After it is fully developed let it hang to dry.
You might be a little concerned that a good portion of the photographs tones washed away down the sink, especially if you have a lighter toned image,
but don't worry, you will print them back in with the next layer.
>> Once the first layer is dry, (maybe an hour or two
later) mix up your second layer of emulsion, this time using only 1 dot
of pigment. This will allow for this layer
to be a light transparent gray as opposed to a brooding black. Take a
deep breath, and coat this 2nd emulsion layer on top of the first layer
of the print that you just made. It should be fairly transparent, and
you should be able to see the previous printing beneath your new layer of emulsion.
>> Now get the same negative again, and once the
Emulsion is dry (another hour or so later) carefully register the
negative into place. Go to the next tutorial for more tips on registering multiple layers. Print this
second layer at 3x your minimum exposure time, since that is what we
used for the high end of our average scale in the last section. I expose
my second layer for 12 minutes. Sometimes I want to print very high into the highlights and I will expose the emulsion for 24 or even 36 minutes using a fairly transparent layer. This was the purpose or the "safety catches" described in advanced negative 4
>> Develop this second layer normally. This time it
might be 3 minutes or so before any pigment starts to wash away in the highlights. Once
it's finished developing, you should have a pretty decent print in your
hands!
