Stain Free Brush Toning Cyanotypes with Tannic Acid

[Alan Townsend]

I've been experimenting with tannic acid toning of cyanotypes on the cheapest watercolor paper I can get at Walmart (Grumbacher), and finally have very good results. This method can also be used on higher quality papers with similar results. It greatly speeds up the toning process (5 minutes) and minimizes the amount of tannic acid used (about a tablespoon of 5% solution per 8x10 print). This method also gives a predictable, repeatable result when used with care, something always missing with cyanotype toning.

This toning can give a range of tones from cool tones to almost neutral tones, to brown-black tones with good permanence. Cyanotype images are made of prussian blue that is chemically ferric ferrocyanide. Tannic acid reacts with this pigment to form ferric tannate, which is the pigment used in iron gall ink that the US Constitution, and parts of the bible are written on.

The problems with tannic acid toning include unreatability, high cost and strong tendency to stain the paper reducing the brightness of the whites. Thirty years ago I had fair results using a moderately expensive watercolor paper for this, but this last year found the Walmart el cheapo watercolor paper to look like a brown paper bag after this toning, so decided to do some experiments to make this work.

For this discussion, I'm using the "classic cyanotype" chemistry that's been around 125 years using ferric ammonium citrate and potassium ferricyanide. For this, we start with a printed and washed for at least ten minute print that's still wet, or a pre-wetted for 2 minutes print from a previous session.

1. Squeegee the print face up on a smooth surface.

2. Using a foam brush, gently apply a uniform coating of 1% tannic acid solution to the print surface fairly quickly, in about 10 seconds, and then leave on for a timed period of a minute and repeat this process from 0 to 3 times more depending on desired tone. Work swiftly to minimize the time tannic acid solution contacts your print. I water down a 5% stock solution for this as needed. Keep this in the dark for storage.

3. Squeegee solution off surface of print and blot with paper towel pressed down, or using a dampened sponge carefully to remove as much solution as possible.

4. Wash print for at least 10 minutes, then hang to dry.

The wet print will appear to be only slightly toned. To judge toning effect, the print must be dry for about 48 hours. Done properly, only a tiny bit of staining will occur with even the most chalk-filled papers. I believe this is caused by formation of calcium tannate as a function of the amount of tanic acid that gets absorbed into the print, so we minimize the amount with this method. Other by-products of the tanning may also be responsible, such as ferrocyanide ions reacting with other paper ingredients.

I do not bleach the prints, but use the length of the final washing bath to control the remaining blue tones. The brown tone does not wash out much, while the blue tone does. For more bluish, shorten that final was from 10 to maybe 5 minutes. For more brownish, extend the wash as needed. As long as you do everything the same, you will get the same result. Variable results are due to variable amounts of solution, strength of solution, time in solution, and amounts of chalk and other chemicals in paper.

1 brushing yields darker more neutral blue tone.
2 brushings yield darker nearly neutral tone.
3 brushings yield darker brown black tone.
4 brushings yield darkest more brownish black tone.

Have fun with it,

Alan Townsend

[Alan Townsend]

Just did some more testing using dry prints instead of wet with even better results from staining, but requiring stronger tannic acid.

Fasten a dry classic cyanotype print down to a flat surface using clips or tape. Spread a 2%-10% tannic acid solution over the print fairly quickly in about ten seconds using a brush and a measured amount the same as the amount of sensitizer that is normally applied and start a 60 second timer. When timed out, use a dampened sponge to blot the solution off the print surface, then wash for ten minutes. This gives the most stain free results, slightly better than the earlier wet method, but I haven't been able to calibrate the effects yet.

2.5% gives a purplish almost neutral image
5% gives a slightly warm neutral image
10% gives a brown black tone.

Applying tannic acid toner exactly like the sensitizer was applied puts the toner exactly where needed on the surface of the print where the image is, and nowhere it's not needed. This makes toning a surface treatment rather than a bulk treatment. We don't sensitize by soaking the paper in a tray of sensitizer.

I'm transitioning from classic cyanotype to simple cyanotype in the next few weeks, but expect similar gains in toner performance. I will likely need a similar method of bleaching the surface only provided the simple cyanotype high contrast version will work with this cheap paper. Otherwise, I will use my better quality paper for that.

Comments or suggestions very welcome,

Alan Townsend

[diagonale-du-flou]

Thanks for the informations !

if I understand correctly, the idea is to spread toner only on the printed surface of the paper?
Have you tried using the brush to treat only certain areas, shadows for example?

Hubert

[Alan Townsend]

Thanks for the informations !

if I understand correctly, the idea is to spread toner only on the printed surface of the paper?
Have you tried using the brush to treat only certain areas, shadows for example?

Hubert

Yes, coat the printed surface only. Not tried selective toning yet, but it may be workable, depending on amount of bleeding. You would need to work fast before too much soaks into the paper. Also, you do not see the tone until after a few minutes of washing, so that makes it more difficult. I do woodland photography, and may want to tone tree trunks brown, for example, but overall I like to have more neutral/warmtone looks than only blue tones.