Solution B. 2 teaspoons sodium carbonate in 1000 cc water. (Note: I have this as 15 grams in my notes, a measurement made by an assistant flake some years ago. A student this year tells me 2 tsps is NOT 15 grams. Whatever, as noted above, timing & strength very flexible. We generally use the dry measure.)
Start by immersing the print (pre-soaked or dry, but not right out of wash water from being made -- has to dry/harden first) in solution A, tannic acid. Take two minutes as your base time if you want to be quantitatively authoritative; but this is one of the ones we do by feel.
Now rinse in clear water for maybe a minute. I think this is to preserve your solution B......
Bathe print briefly (less than minute) in B and rinse again. Now BACK into A, which is where the color happens. Watch carefully and if you want a split tone, snatch the print out BEFORE it gets to the color you want because, just as in ferricyanide bleaching, chemical remains in the paper and action continues after it's in the rinse bath.
Strictly speaking, to save lots of changing of water, you need 3 rinse trays -- one for after the first tannic bath; one for after the first carbonate bath, and one for the finished print. But this is honored in the breach, so to speak (in the bleach?).
If, BTW, you're not happy with the tone, you can continue back and forth. You may ruin it, you may contaminate the baths, you may turn any of them or the rinse bath into a toner itself by carry-over. But the idea is to spoil prints -- and come up with just a few wonderful, special, precious ones. Cyanotype is too easy anyway.
I give students more or less the advice above & they go their own way. Some like to use very small amounts as a one-shot toner. Others seem able to use and use and use one set of baths without getting strong paper base stain (which is the pitfall to look out for). And one student today brought in toned cyanotype where the paperbase was fairly stained, "harmonizing" a too-contrasty print.
A similar formula, by the way, uses about 15 drops of household ammonia per ounce (30cc) of water for the B solution and a much stronger tannic acid for the B solution (10 grams per litre). My notes on this say bleach first in the ammonia and tone on the tannic until the desired color. I found this worked years ago, and students have used it with good results. But the one we generally do in class is the sodium carbonate & that's the one I'm most comfortable & familiar with.
Remember, the toning does cost density, so you want to start with a print that borders on (or is well into) too dark. I suggest also starting with at least two identical 21-step prints, tone one and keep other for comparison -- see where split happens, how much density is lost, if midtones flatten out, etc. And of course no law says you have to do split tone -- you can go all the way to chocolate, also nice.
From: Judy Seigel
From: Risa S. Horowitz