Quote Originally Posted by kevin klein View Post
The cyanotypes I have been making latly seem to take much longer to expose (two to three times) than they did when I started about eight years ago. Does the dry chemical break down after a few years and not work as well?
Global warming.

Also, what can I do to decrease or increase the contrast?, use more or less of one of the two chemicals?
Here ya go:

Different ratios of parts A & B on two different varieties of Crane's Kid Finish paper using the traditional cyanotype chemicals (ferric ammonium citrate and potassium ferricyanide). I don't recall which iron salt is 8% and which is 20% solution, but at 1A+1B it is the normal recipe. The strips are arranged 2A+1B, 1A + 1B, 1A + 2B, and then 1A + 1B again (labelled "citric").

It has been a long time since I tested this, so forgive any memory gaps. It looks like this test was done with a NuArc exposure unit at 1120 units for all! Citric acid speeds it up but it bleeds. (Can't remember if this was a pretreatment, addition, or all rinses using 2% citric acid solution but I suspect the latter.) The faint penciled arrows indicate the step to which the exposure solarized before processing. Though I'm not completely sure, I would suspect these were all coated and dried, then exposed and processed together 'cause that's how I roll.