The chapter called “One interpretation of gum printing” of Sarah Van Keuren’s book “A Non-Silver Manual: Cyanotype, Vandyke Brown, Palladium & Gum Bichromate with instructions for making light-resists including pinhole photography”, written by Melissa Good.
I am more than willing to share any information for others to learn and grow from.
Preparation for Negative:
As for my image, I scan a 35mm color negative on a flat bed scanner at 1200 dpi at 100%, do touch-ups in Photoshop, change the image to black & white, invert the image, and adjust the image with curves and sometimes levels.
Printing the Negative:
Try experimenting with different kinds of inkjet transparency films, by purchasing either sample packs or just a few different film packs of various brands, to see which film will work best with your printer and medium you are working in. I initially did test prints with various inkjet transparency films, but the film I have been working with has been discontinued (luckily I have a bit of back stock to work with). When I print out the image, I go to print options and “scaled to fit media” in the Epson dialog box. From an Epson printer, I then print out the image as an “Ink Jet Back Light Film”, SuperFine – 1440, Color, Error Diffusion, click on “Microweave and Super” and then print out the image. This is how I get the single negative from which I make an in-color gum print. Through experimentation you may find something that works best for your setup.
I let the ink on the negative dry overnight by hanging it from a clothesline or on a corkboard with pushpins. I have not had a problem with smearing, but if it went underwater I am sure it would smear. I have to say that although I am not the most gentle handler of my negatives, the negatives usually do not get too banged up; however, the most I have used a negative is for 3 different gum prints with varying numbers of layers.
I do not do the typical version of sizing paper. The way I do my paper (BFK Rives) is that I preshrink the paper as described in the gum chapter by Sarah and I let the paper dry completely. I then coat my paper with two layers of gelatin using a sponge brush. The way that I was originally taught was to then soak my paper in diluted formaldehyde, which hardens the gelatin. I have skipped on using the formaldehyde with my prints because of the health hazard of using it (without proper ventilation it is not a good idea to use this chemical). After long discussions on the benefits of using or not using formaldehyde I have come to the conclusion that it is fine not to use formaldehyde as long as you print over top of any gelatin and do not use gelatin as your last layer in gum printing. As for how often I use gelatin between layers, I usually do not recoat my paper with gelatin after the initial coating. Currently my work, has no more than seven to eight layers. In the past I have worked with up to 10 or 12 layers of gum pigment, re-coating with gelatin one to three times throughout the printing process, but I would sometimes end up with crackling in my print, which I attributed to the gelatin layers.
Good luck with gum printing, take notes, allow for accidents and have fun.