View Full Version : Clearing Cyanotypes

Clint Chadwick
21-Mar-2011, 05:40
After getting some help in here figuring out how to mask my cyanotype prints I have made a few test prints, but am a bit dissapointed by the results.

It seems that the cyanotype sensitizer never completely clears from the paper and ends up turning a particularly unnattractive yellowish brown once the print dries. Please see the attached picture.

I thought maybe it was my paper selection (Canson Montval 300g), but I tried again with the Fabriano Aristico that came with my Fotospeed cyanotype kit and the results were the same.

I am washing the exposed print in a slightly acidic initial bath for 5 minutes and then in another plain water bath for 20 minutes.

Is anyone able to fully clear the sensitizer on a cyanotype (what's the secret?) or is this why people don't often mask cyanotypes?

21-Mar-2011, 05:55
Perhaps you could contact Fotospeed for ideas too?

I use the Bostick and Sullivan's cyanotype kit and haven't had any visible sensitizer left after washing with the three papers I've tried it on.

James Hilton
21-Mar-2011, 06:20
Clint, is it the original Cyanotype formula, or the new one? If it is the new one I think you should wash in a citric acid bath to clear all the yellow (1 heaped teaspoon of citric acid crystals in 300ml of water is a good starting point).

The yellow tinge is due to incomplete clearing, and is usually a result of paper incompatibility, or water PH. Do you know if your water is alkaline?

Are you using Canson Montval watercolour paper, or inkjet paper? If it is inkjet paper then it will be because of the recieving layer (the same happens with Epson HW Matt paper).

What is your washing agitation like, continuous or not?

Simon Howers
31-Mar-2011, 05:15
clearing cyanotype is usually pretty simple, you just have to wash in running water for long enough.

A couple of points:

With Type 2 cyanotype (The Mike Ware formula) you must use a citric acid bath. With absorbent papers - like Arches Platine, it can take 24 hours for the print to fully stabilise. If you are in hurry to see results, try a weak hydrogen peroxide bath.

The process is quite paper sensitive. Specially developed papers like "Buxton" have reduced absobency whilst not containing any of the buffers etc. which cause problems with iron-based processes. This improves the washing process.

Simon Howers
Micklethwaite Landscapes

Clint Chadwick
31-Mar-2011, 05:28
Thanks for the assistance.

The problem was the citric acid bath. According the Dr. Ware all that is required is a weak acid bath so I was using acetic acid (straight vinegar). Switching to a citric acid bath fixed the problem and cleared the print well.

I am not sure if the vinegar is insufficiently acidic or if there is a property of it that makes it ill-suited for this purpose.

Vlad Soare
2-Apr-2011, 03:48
I am not sure if the vinegar is insufficiently acidic or if there is a property of it that makes it ill-suited for this purpose.
A weak acidic bath alone does not guarantee good clearing. It is recommended simply because Prussian blue is soluble in basic solutions, and tap water is often slightly basic.
Citric acid has an affinity for ferric ions and helps with their removal from the paper's fibers by forming soluble compounds with them. This is a good thing with iron-silver processes, where you want to get rid of every trace of iron, but I'm not sure how it affects cyanotypes, considering that in this case the image itself is made of iron salts. Acetic acid doesn't do this. So, while acetic acid merely provides a pH low enough to avoid the washing out of the Prussian blue, citric acid plays an active role in the clearing process.

Ole Tjugen
2-Apr-2011, 06:48
If citric acid doesn't do the trick, try oxalic acid.

citric acid and oxalic acid both form soluble chelates with iron, but oxalic acid has a much stronger effect.