I spent the past couple days wrestling with classic cyanotype. This is somewhat embarrassing, given the supposed ease with which this most basic of processes can be done. Invented by John Herschel (a famous polymath) in 1842, it is simplicity itself. Two chemicals, expose in sun, develop in water, dry. Voilà! Anna Atkins created the first photography book consisting of sublime photograms of British Algae using this process.
Above is the cyanotype paper after a 6 minute UV exposure and before water development. Note the dark tone reversal (Prussian White, which reverses back to Prussian Blue on oxidation in air).
I've had two problems. Well, maybe there's a third one.
First, I've had runoff of the emulsion in the water wash. At various times as I've approached this process I've made small steps of progress. The cyanotype process does not like alkaline environments. Papers, contamination, or water. I purchased an Extech PH100 meter to determine that my tap water was alkaline (8.5 pH). So I now acidify my water a bit. I tried several papers as I've mentioned before. Crane's Platinotype and Crane's Weston Diploma had a lot of emulsion runoff for me. Bergger COT-320 (my preferred palladium printing paper) did not work well either. It has been somewhat frustrating in that I spend a bit of time with it and then go off to work on something else and return after a period of months to consider it again.
Obviously I'm not really worrying about this.
Mark Nelson told me that Sam Wang clears his cyanotypes by simply inverting the paper in a tray of water and letting it quietly sit. I was washing the paper, and fiddling with it as I had done for palladium prints. Sam's method is simple and helps reduce the runoff. In trading e-mails with him in the past couple days he said he clears his prints for "5 to 10 minutes" in reaction to my 30 minute clearing stake in the ground ("Life's too short to wait half an hour!", to which I agree).
The biggest reduction in runoff I've gotten is from switching to Arches Platine, per Mark Nelson's suggestion of Christina Z. Anderson's preferred paper for cyanotype (I think?). I am able to smoothly rod coat it, making sufficient passes to get an even coat without puddling of emulsion on the surface. Crane's papers buckled quickly before absorbing the cyanotype emulsion when I tried rod coating before - and then would abrade on hake brush coating making the surface rough. I air dry the Arches paper and then bring it to bone dry with a hair dryer before exposure.
The struggle this weekend on runoff has to do with exposure time. I was told early on during one of my attempts that underexposure will result in emulsion runoff. And I seemed to verify this weekend that a 20 minute exposure had little or no runoff. However, I ended up with an overexposed print (as measured by a Stouffer 31 step wedge designed by Mark Nelson and available on his web site). This irks me - I prefer not to overexpose prints handspring in compensation around it. When I dropped exposure time to eliminate the blocking of shadows in the step wedge, runoff occurred. My goal is at this point to keep it to a minimum.
The second problem I've been having is bleeding of the Prussian Blue into the highlights. This was truly problematic with Crane's Platinotype. A white highlight was not in my ability to pull of with that paper. The technique of fast oxidation by dipping the cleared print briefly in a water bath with a small amount of hydrogen peroxide made the bleeding much worse. Two changes seem to have solved this problem. First, Arches Platine is the cyanotype wonder paper in my book. It is bleed resistant. The second factor was some recent experiments by Chris Anderson. Her web page illustrates the bleeding issue well. The short of it is reducing the proportion of the ferric ammonium citrate in the emulsion eliminated bleeding. My emulsion is now 1 part water, 1 part Solution A (20 gm ferric ammonium citrate/100 ml distilled water), 2 parts Solution B (8 gm potassium ferricyanide/100 ml distilled water), and one drop of Tween 20 10% solution per 60 drops of emulsion. The Tween 20 help to spread the emulsion uniformly and I added after seeing some beading of the emulsion on the paper during coating. A little goes a long way.
So, much progress was made this weekend. To the right is the developed print after a 7 minute inverted clearing in a mildly acidified water bath, followed by a 30 second inverted immersion in a water bath to which a splash of hydrogen peroxide was added. The bleeding problem is non-existent - I lay the paper flat on a blue shop paper towel and press another sheet on top to remove the excess water before allowing to air dry.
I'm now struggling with blocking in shadows. Looking for some insights from Mark at this point.
My third problem is one perhaps of perfectionism. Yes, cyanotype is an easy process. But I'm thinking like any printing process (especially alternative processes) it is easy to get a print. To get an excellent print, and to be able to reproduce that feat for other images. Ah, there's the rub.
Tomorrow is another day, I'll take my wins to bed.