Toning cyanotypes to black
I’ve been using cyanotypes under gum bichromate as my cyan layer of a tri-color or quad-color print. This process gives finer detail than gum, has a relatively low toxicity level, is highly stable in oxygen and sunlight, and the emulsion rinses out of the paper faster. All of this makes it an ideal first layer under gum bichromate.
Tri-color gum over cyanotype.
I wanted to try using cyanotypes alone to do more environmentally-friendly monochromatic printing, but I didn’t want them to be blue. The blue of cyanotypes happens to be my favorite color, but it’s very distinctive and not for everyone. I was happy to learn you can tone cyanotypes to pretty much any color using botanicals, so I took a stab at toning to black and brown using wine tannin and oak gall.
Before you read further, read my post about cyanotypes and pH if you haven’t already. Toning cyanotypes in a bit of a crash course in chemistry. Cyanotypes are very stable iron compounds that do not degrade in oxygen or light, and are relatively stable in weak or dilute acids. This means that while they are very archival, they also do not tone easily. You need to introduce an alkaline element to break down the atoms enough to allow dyes (tannins) to bond to the iron. Some people with harder water report they don’t need to bleach their cyanotypes first. I live in Seattle, with our neutral pH 7.0 water from the Cascades mountains, so I bleach first.
Toning Step-by-step
After your print has been bleached and dried, it’s ready to tone. I used powdered wine tannin for my first attempt and oak gall for my second. I think I prefer the results of wine tannin better, though the oak gall lasts longer and allows me to make more prints before it loses its potency. Here is my process using wine tannin step-by-step:
Prepare your toner according to instructions. I recommend you start with wine tannin. It’s easy to use, stable, and cheap. It gives a strong, warm, purplish-black color, and though it is susceptible to staining I have found that is minimized by keeping the temperature down.
Rinse your print for two minutes to get it thoroughly wet, then wipe or drip off extra water.
Transfer to the toner bath and be prepared to babysit. Your choice of toner, it's freshness, temperature, pH of water, solubility in water, and ratio of material to water will all impact how long your toning process might take. As a rule of thumb for wine tannin, when the paper itself looks slightly purplish when you pull it out of the toner, and the parts of the image that used to be blue, then yellow, are now a warm black, it is ready. You can always re-tone if you didn’t tone long enough. You can’t walk a paper back from staining.
Rinse your print for 15 minutes in neutral pH, room temperature water.
Dry paper until it is bone dry and assess.
Your print will darken and become more matte upon drying, so keep that in mind when deciding if it is done.
Gum Over Toned Cyanotype
I experimented with trying to use the cyanotype layer as my black, thinking that if I could get great detail with the black layer I’d have a crisper image overall. The idea was that I would tone a cyanotype layer, then in gum do a yellow, magenta, and blue layer on top of that for a CMYK print. I printed, bleached, and toned the cyanotype and was happy with the black layer. Once dry, I noticed that the paper itself had gone all soft, as if the fibers had opened up and become more porous and “fluffy,” compared to how it felt after a normal cyanotype layer. I didn’t think much of it, until I put down a blank layer of gum and dichromate as a type of sizing (some people refer to it as a blind layer but I’m not a fan of that term), which I typically do as part of my gum over cyanotype process. When I laid down the gum and dichromate, the print immediately went dark brown. The paper didn’t repel any emulsion at all: it was thirsty like a sponge, and was also immediately ruined. It was clear that all the dichromate had sunk into the paper as if there was no sizing whatsoever anymore.
I’m not quite sure what happened, but I suspect it was due to the increased pH. If anyone with a better understanding of chemistry knows what happened there, please leave your thoughts in the comments.