Washing your cyanotype in the best way is very important in order to have a print that will last beautifully.
If you don’t wash enough, some emulsion will remain inside the paper and it will show up in time as a yellow cast in the highlights.
If you wash too much, you risk to wash off a bit of the darker areas of your print and so to reduce its overall contrast.
Water temperature, water pH, washing time, speed of agitation (rocking) are all factors that may give you a difference. You want to find your own way to develop and wash and keep it consistent, from the first test prints during the digital negative calibration to your real photo prints, because also from that depends the reliability of your digital negative calibration, and at the end the quality of your print.
I found that for my process with Arches Platine (a process consists of the sum of all the darkroom and printing variables including emulsion type, paper type, relative humidity, type of coating, etc) the best washing time was 20 minutes in total.
My tap water is alkaline and to compensate it I need to use a little citric acid as follows. This is valid only for me, you need to check the pH of your tap water, for that I suggest you to use the liquid tests for aquariums which are more reliable than the paper strips. Also, I use a certain quantity of citric acid in the first development tray to widen the exposure scale in my prints but I’ll write more on that in a specific post.
For a 30×40 cm (12×16 inches ca.) print on Arches Platine and classic cyanotype my 3 trays are configured this way:
- first tray: 2 liters of water with 5 ml/l (in 10% solution) citric acid, constantly rocking by hand for 3 minutes, print face up to avoid air bubble formations, with a continuous and rather quick (but not too much) rocking at least in the first minute when developing occurs to prevent staining from bleeding.
- second tray: 10 liters of water with 0,3 ml/l (in 10% solution) citric acid, I use a small submerged aquarium pump because I get bored, (hence the 10 liters, otherwise 5 liters are enough if my pump can stay beside the print inside my tray) for moving water for 3 minutes, print face down, to clear most of the emulsion.
- third tray: 5 liters of water with 0,3 ml/l (in 10% solution) citric acid, gently rocking by hand from time to time for the last 14 minutes, print face down.
For smaller prints like 25×25 cm (10×10 inches) I use 2 liters, 5 liters and 5 liters respectively in my 3 trays and if the prints are smaller I reuse the water of the second and third tray for washing more prints. I always change the water in the first tray for each print.
Washing for a total of 15 minutes was also good but the paper white was best at 20 mins, so that’s my washing variable defined for a perfect digital negative.