In order to make any kind of gum print other then a solid block
of color, you need to first make shadows by use of a negative or objects. Gum
prints are contact prints, requiring that the negative be the same size as the
intended size of the final print. The creation of negatives used to be done in
the darkroom, or even with large format cameras themselves. A new and very
successful way of making enlarged negatives is emerging. Now with photo inkjet
printers, it is possible to print and control the density of ink on transparency
film to make perfect negatives for
full scale gum printing. I enjoy this blending of old craft and new technology to
help me make my prints. That's what Photography has always been about!
This tutorial is for basic Digital Inkjet Negative Creation for Beginners who are new to gum bichromate printing.
Photo Quality Inkjet Printer (I have an
Epson Stylus c66*)
*the inks used must be able to block ultraviolet light. I used
cheap inks once and found that light would go straight through those negatives, no matter if the density were nearly solid
black!
Inks used should be resistant to fading, thus containing something to block UV light
Inkjet Transparencies (I get them from Office Depot)
Some kind of image editing software (like
Adobe Photoshop)
Step One: Understanding Digital
Images
To go any further, it is necessary to explain how images can be
stored digitally in the first place. Don't worry I won't get too technical here.
A digital image file is made up of pixels, they are the tiny
squares of color I'm sure most of you have seen. Each pixel is really a piece of
digital information specifying where it is in the image and what color it is.
All we are concerned with is the color, or value, of the pixel.
Typical 8-bit Digital Images have 256 levels of value per channel. A black and
white image is a one channel image. The values go all the way from black to white with
each value of gray specified by a number between 0 and 255. 0 is the number that means
black to a computer, 255 means white, 128 or so means middle gray. Digital images have a
relatively LONG
SCALE with 256 different values for each shade of gray.
Color images have 3 channels, opposed to the 1 channel that a black and white image contains. A color images channels are of red, green,
and blue, each channel containing 256 levels of value, meaning there are 256 x 256 x 256 = over 16
million colors of pixels in typical color digital images!!
In the real world that our eyes see, light levels change in ever
more discrete amounts and over a vastly greater range then 256 levels of
brightness.
Step Two: Understanding Scale
As you can see above, digital images have many values of grays
from black to white within them. An image containing all the values would have a
full scale. Instead of thinking of a scale with the numbers 0 - 255 like a
computer, we can think of the values in something more familiar: percentages.
The percentage represents the amount of black. 100% is total black, 50% middle
gray, 0% is white of course. Ansel Adams' Zone System divides the scale
into 10% increments. The image below illustrates a scale in 2% increments.
Your monitor should have the right contrast and brightness
settings to be
able to see each 2% increment distinctly.
In our computer and on our monitor, black is at 100% and white
falls at 0% where it should fall. If we were to print this exactly as it
is onto a transparency, and use that as a negative for gum printing, we would
loose a great portion of our scale in our Gum Print. Why? This is because Gum printing is a very
high contrast, short-scale photographic process.
If we were to print the above scale we would inevitably,
depending on exposure time, light source, pigments used, development and a host of other
variables, end up with something that looks more or less like the scale below:
(Remember, black on the negative will block
out light and cause the emulsion to wash off during development, revealing the
paper below, this is why 100% is now white in this scale.)
In the above Image, we see that the high contrast of the gum
caused us to loose about 2/3rds of
the information on our negative and in our image! Every thing in our negative
above 70% is washed to white and below about 35% is exposed completely. Below is a simulated example
of an image loosing all of that detail in the printing process.
The high contrast of Gum printing is
not a bad thing! It can be worked with!
With the above image you could underexpose the print and reveal
more of the buildings, but less of the sky detail. You could also over expose
the print and get more detail in the sky if you wished.
There is a layering
technique which I describe in Printing with Custom
Negatives where you first print a light color
then a darker color at different exposures to compensate for loss of detail from
your negative.
Step Three: Getting a Digital Image
In order to edit images on a computer, you need
some way of getting your image into a digital file. If you have only a print,
you could scan it using a flatbed scanner. Perhaps you have a digital camera and
your images are already digitized, you need only to download them to your computer. Or, you are like me, and have 35mm film
negatives everywhere. I bought a Minolta 35mm negative/slide scanner a few years
back to make high resolution scans of my negatives. Now, however, I finally have a digital
SLR camera of my own!
You could even create
non-photographic images
on your computer for printing. Really it doesn't matter how you do it or what
you use, just that in the end
you need some sort of digital image file.
The image should at least have a good resolution at 8x10 inches to keep
details.... a resolution of about 300 ppi is perfect.
Step Four: Your First Negative
By now you should at least realize that the scale of digital
files is much longer then the scale of one layer of gum, and as a result you
will end up with an image of much higher contrast in your gum print. There are two solutions to
the problem:
Start with an extremely low contrast image with mostly middle gray values
containing little or no black or white, and it will increase the image contrast
to "normal" amounts (or thereabout) when you print it with Gum,
if you are lucky.
OR: you can start with an image that is already very high contrast, where most
subtle dark and light tones are already lost, or just use an image where high
contrast might look good!
Some simple steps for making your first negative:
Open your image file in an image editing software program
like Photoshop
Invert your image values to negative. In Photoshop you can go to
Image>adjust>invert or hit Ctrl+I
Flip your image horizontally (this is because you will put the transparency ink-side down during exposure
which will reverse left and right in the image)
Resize your image so that it will fit onto your
transparency sheet.
Print your negative Image on transparency film with your
printer's glossy paper settings. (Some printers have a setting for
Transparency film, however I don't use the setting. I use the setting for
glossy photo paper which prints a heavier amount of ink on the transparency
film, and allows for finer detail.)
To go any further, it is necessary to explain how images can be
stored digitally in the first place. Don't worry I won't get too technical here.
