Students have heard me utter those words many times while teaching alternative processes. With so many variables to control with gum printing, it makes consistency hard to come by at times.
It’s been a few months since I’ve printed but I left feeling confident. Having this week off, I decided to go back into the darkroom to print some old images. I spent the weekend making negatives and mixed up new chemicals—I was ready. However, I went to turn on my exposure unit only to discover that the fluorescent black light bulbs would not come on. After spending half the day fussing with it, I went to Lowes to buy four new light fixtures to replace the old ones I had (which were probably about 10 years old). I installed the new fixtures and now the lights work fine. Problem solved—not quite.
After developing the first layer, I realized my exposure times were off (due to the new fixtures no doubt—since it was the only variable that had changes since my last printing session). Gum always finds a way to keep me humble and otherwise frustrated.
Since printing full color gum prints uses multiple negatives (Cyan, Magenta and Yellow), a system for registering is required.
I start with the Cyan negative first (since it prints the darkest) by cutting off the four corners of the negatives.
Next, I lay the Cyan negative on top of the Magenta negative on a light table and then, with a Lupe, I line up the registration marks.
Working from opposite corners, I tape each corner of the Cyan negative to the Magenta negative after they are aligned.
Using a pushpin, I punch a hole in the center of each registration mark.
The Cyan negative is now registered to the Magenta negative. I then remove the Cyan negative and repeat the procedure with the Yellow negative. Once all three negatives are registered, the next step is to register the negatives to the paper. I usually start printing with the Magenta layer followed by the Yellow negative and finally the Cyan negative. I place the Magenta layer on the sized paper and, working from opposite corners, punch a hole through the negative’s pre-punched registration marks into the paper.
I tape the negative to the paper and remove the pushpins.
Now I’m ready to place the print with the attached negative into the contact-printing frame.
Use the highest resolution file for best results (in the past, I was using 4×5 negatives and making high res scans, now I’m using the Canon 5D Mark II).
In order to get the curves I needed to print CMY negatives in Gum I came up with an ink jet gray scale using the Epson 1400 printer that was equivalent to the Stouffer 21-Step Sensitivity Guide. Knowing that Gum can only print a total of 8 steps (from step #2 to step #9), I used a densitometer (the X-Rite 331 Densitometer) to measure each of the steps (from 2-9) on the Stouffer 21-Step Sensitivity Guide and came up with a numerical value that I could use to match against an ink jet gray scale using Pictorico ULTRA PREMIUM OHP Transparency film. Making wedges in Photoshop and filling in each wedge with different percentages of black ink I came up with a ink jet gray scale that is equivalent to that of the Stouffer 21-Step Sensitivity guide (give or take .02). To apply this ink jet gray scale, I used Photoshop CS5 and in curves, I made 8 points (to represent the 8 steps that Gum can print) and changed the input and output accordingly:
Input 0% – Output 22%
Input 16% – Output 52%
Input 30% – Output 65%
Input 44% – Output 72%
Input 58% – Output 76%
Input 72% – Output 80%
Input 86% – Output 83%
Input 100% – Output 85%
“Pulling up” on the “top” of the curve (even 1%) to an output greater than 85% will increase the contrast of the negative while “pulling down” on the output below 85% will reduce the contrast. Using a different printer is one of those variables that will alter the results of the negative.
Making the Master Template
In Photoshop, I start with a “canvas” the size of the media I’m using (13×19 inches). I fill the background with 100% black (which will print white). In four corners I place the registration marks.
Then I place the four step tablets (YMC, Y, M, C) on the top of the negative making sure each one (except the YMC step tablet) is a separate layer that can be removed later.
Then I place an image as a “place holder” for positioning the negatives (also a separate layer to be removed later).