Cyanotype with green stains after wash

Hey there! I've recently started making cyanotype prints, mostly via digital negatives. I am using a UV lamp for the exposures. The first print I made has been my most successful so far. It dried and oxidized to a deep blue and I am pleased with the exposure. Most of my others have dried blue but with green stains on them, often in an X shape over the paper. For most of the prints I have exposed them for 15-30 minutes and then developed for 5 minutes. I added vinegar to help with the pH of the water. For the most recent print, I followed these steps and then washed in fresh water for an additional 10 minutes. I thought this may solve the issue with the green stains but it didn't seem to affect the print whatsoever. I'm curious as to why my first print was fine but the others have been retaining green.

I mix the liquid solution, paint the papers, leave to dry for 1.5-2 hours in the dark (at times overnight but the results have been the same with those dried for less time), and then expose, develop, wash, leave to dry in the dark.

Here is a picture of the first print and the others with the staining. Thanks so much for your help!

What paper??

Peter Schrager said:

What paper??

Click to expand...

It’s a canvas paper that I’ve been cutting into smaller pieces, acid free

I've had this before with some canvas textured paper - impurities in the paper. Funny shapes are cased by the rapid drying process of the paper in the manufacturing process in some way I suspect.

You could try an acid bath prior to coating. "Acid free" usually means they added an alkaline chemical to the paper (like calcium carbonate). These don't always react well with the traditional cyanotype formula, in my experience. I haven't experienced yellow staining from it, so it might not address your specific issue, but a quick dip in an acid bath and a thorough wash would at least help to clear some of the excess chemicals used during the paper production process, and might make the paper more suitable for cyanotype printing.

You'll want to research how to acidify papers for cyanotypes. There are a lot of different formulas and methods, and I'm not sure which is best. I use a highly diluted amount of HCl, since I have plenty of that chemical and no other real use for it. But most people use another acid that's less dangerous to work with.

Sulfamic acid available at home depot
Use a 10% solution for 20 minutes
Wash afterwards

I've been acidifying various papers that have alkaline buffers for a few years now. I only soak in the acid (sulfamic 10%) for only 5 minutes, then use the Ilford method of washing. Sulfamic acid is powerful stuff. Wear gloves and have ample ventilation. I bought mine from a chemical supplier. Hardware stores were quite expensive. You can also use vinegar. Use it straight from the bottle. 5 to 10 min. followed by a good rinse in water.

Another thought. If the cyanotype solution soaks all the way through the paper when you coat it ( it looks like it does in your pictures ) then it can be contaminated by what is under the paper when it's coated. Recently I coated some thin paper that was taped to cardboard, and where it soaked all the way through and touched the cardboard the paper was fogged...

Could also be that you have not washed thoroughly (does this "X" perhaps part of the plastic moulding of the tray?).
A short dip in 3% (15gr. - 500ml H2O) Metabisulphite may clear the yellow stain.
It is possible too that the canvas has not dried completely (use a hair drier prior to exposing & be sure it is dry).
Just a thought...
Good luck, the big print is very nice.

PS. Your development of 5-8mins would be okay but change the water and wash for additional 30-45mins. This could be the yellow stain's origin, lack of complete wash.

Thank you everyone for the information and tips! As a beginner with this process it's great to hear from you all. After coating the paper with cyanotype, I have left it to dry untaped to anything, so it's kind of bowed. A friend of mine said that could be what caused the X pattern. Maybe just how the chemicals have dried with the paper in that curved shape. I'd say it isn't due to the molding of the tray since I'm using a large one and agitating the print, but that was a good idea too. I'm going to try a few different variables over the next week. Soaking in vinegar/washing/drying before coating/exposing. Gently using a hair dryer before I expose. Coating and drying flat, maybe I can pin the corners down. I will check back in to say what worked/what didn't for this paper. I also bought a pad of canon 140lb watercolor paper today to try out. If anyone else has any other suggestions I would love to hear them. Thanks again!