Support for hydrochloric acid cyanotype

Hydrochloric acid is often cited as cyanotype support. It is said to augment blue dmax, giving a darker and deeper hue to shadows, almost black, but also providing neutral middle tones, such as metallic grey. I found indications on its use as first developing bath (I use very diluted acetic acid or water) or toning-support.

I tried this last procedure, immersing a washed and dried cyanotype in a hydrochloric acid 2% solution for 20’, but the color hasn’t changed at all and the dmax absolutely hasn’t augmented.

I don’t want to try higher concentrations, because hydrochloric acid, more than dangerous, gets paper fibers fragile. I still have to verify if hydrochloric acid as development bath achieve the described results. I wouldn’t be willing to use concentrated acid anyway, since some sources cite the possibility of expansion for cyanide gases when a not perfectly washed cyanotype is bathed in an acid.

Paper developer as alkali in cyanotype toning

Some sources cites ammonia and tannic acid toning as “red brown”, while giving a toning formula of “grey black” that uses a paper developer as alkali bath instead of ammonia or sodium carbonate. I tried this combination too, using a new diluted developer 1+9.

I was expecting a hue slightly different from the ammonia one, not to hope in dmax miracles. I actually obtained wonderful purplish hues, most of all in the tannic acid combinations, some seconds inside the developer and then tannic acid again, but it is absolutely impossible to obtain black cyanotypes without dmax loss during toning.

Black cyanotype is still far away

All of the described cyanotype toning techniques makes splendid results, particular and unique images, delicate hues, optimal gum prints backgrounds, etc… No one that I tried, at least in my case, is able to produce a black toning, intensification or at least a limited dmax loss, which happens every time I tone a cyanotype. A hydrochloric acid bath particularly seems not to influence a washed and dried cyanotype.

Collateral information, a useful forethought consists in using acetic acid baths between alkali and tannic acid to preserve this last solution, sensibly augmenting its life.



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