How to Make 4 Color Negatives for Gum Printing

R-G-B TO GRAYSCALE C-M-Y-K SEPARATIONS
On Pictorico OHP Ultra Premium In Photoshop

Step #1 - Open up your image file and work on it in Photoshop until it meets your expectations and intentions. Save it with a label that will indicate that it is specifically for the particular set of CMYK negatives you are making.

Step #2 - Go to > Menu Bar, then to > Image, then to > Mode, then click >CMYK

Step #3 - Go to > Image, then to > Adjustments, to > Curves and click >Load

Step #4 - Find your > Gum Curve (the. sacv file) and > click Load.

Step #5 - Go to > Image, then to > Adjustments, and click > Invert

Note - You have an option at this point in the process. Some gum printers want a set of negatives that are really “punchy” and have a good deal of contrast. If you are one of these gummists then this is where you will go to > Image, then to >adjustment and click > Auto Levels. If you are seeking a more true to life CMYK interpretation of an actual color set, then you might want to skip this step. Try it
both ways and see what you like. At some point in the process you will be adjusting levels, and by doing so, the contrast levels of your negatives.

Depending on the type of negative separation set you want, contrasty, or sort of true to life, you can adjust now or after you make your separation set.

Step #6 - Next, go to the palette that is probably on your screen, indicating Layers, Channels, and Paths. Click > Channels and, using the tiny arrow on the top right corner of the palette, click > Split Channels. Presto! … Photoshop will automatically create 4 separate, and distinct, B & W negatives for you. These are your CMYK separations.

Step #7 - For each of these negatives… Go to > File and to > Save As. Title your negative to as whatever you need to name the file in order to remember it. I name my sets by the title of the image and what color negative I will be applying when gum printing. i.e., Cyan, Magenta, Yellow or Black.

Step #8 - Go to > Image, then to > Adjustments, and > click Levels and adjust them manually… bringing the left and right adjustment markers to the extreme ends of the Levels histogram. Do this step for each of your separations. Keep in mind that you are making a unique set of negatives here and that you can adjust the contrast of these negatives using Levels or Curves to suit your needs or the type of color you are using. This will make sense once you begin doing the actual gum printing.

Step #10 - Print out the CMYK negative separations using Pictorico OHP ink jet film.