I haven't done much cyanotype in years, but out of curiosity, I have been doing some step wedges lately. I'm running into something odd with my New Cyanotype chemistry. It produces a very short H/D curve, i.e. it prints with very high contrast. This is weird, because I recall when I last used this formula (some 8 years ago or so), I saw the long-scaled curve typical of New Cyanotype, although I didn't do measurements back then.
Here's a collection of curves I've just plotted based on several experiments:
In terms of chemistry, I mixed up three small batches of the New Cyanotype chemistry, and all produce the same results, so it's not a mixing error - or at least not a spurious one. My approach is based on Mike Ware's notes here: https://www.mikeware.co.uk/mikeware/New_Cyanotype_Process.html
* to 2g potassium ferricyanide I add as much hot water to allow it to dissolve (2-3ml), and keep warm in a hot water jacket.
* to 6g ferric ammonium oxalate, I add 6ml hot water and dissolve
* mix together both solutions while still hot
* allow to cool down gradually
* filter the liquid and discard the crystallized out emerald green potassium iron oxalate.
The filtrate ends up being about the volume that Ware recommends, so I didn't add additional water to the stock.
I did not add dichromate, citric acid, a wetting agent or anything else to the stock solution.
I coat with a brush at about 0.5ml for a 5x7" area. I've used several papers (see chart above) without prior treatment. Coated paper is dried with a hairdryer and exposed immediately, and processed immediately after exposure.
Exposure is done with 365nm + 395nm LEDs, but I've also done a test with UV-BL tubes, producing pretty much the same H/D curve for all intents and purposes.
I've tried diluting the stock solution with water, which seems to increase printing speed (consistent with Ware's notes) and reduced dmax, but otherwise no apparent difference in curve shape/length.
I've tried adding a pinch of citric acid to the first wash bath or straight tap water, but see not difference; the prints clear in the same way.
I've tried getting the blue to develop with hydrogen peroxide vs. air-dried/naturally developed blue, and the end result is indistinguishable.
The different papers I've tested produce some differences in dmax, but curve shape is overall similar. The sagging pattern at the shoulder of some of the curves above is probably due to mottling which some papers are prone to; esp. the Schut Laurier paper tends to give some lighter blotches in the darker areas.
The somewhat long toe in some of the prints (e.g. the "Simili Japon #2" plot above) is probably due to incomplete clearing. I limited wash times to avoid bleaching as a result of the slight alkalinity of our moderately hard tap water.
I have also tried adding citric acid to the sensitizer prior to coating. In large quantities, this produced some instant fogging upon drying the paper, but this was below the dmin threshold and washed out in processing entirely. In smaller quantities, there was no apparent effect on the printing qualities or curve.
It's kind of puzzling, since Ware notes an exposure range of around 1.8logE for a full tonal scale print, and I get a full range from dmin to dmax on the paper with only around 0.6logE exposure range. In fact, the curve I get with the New chemistry is steeper than with Classic!
I'm sure I must be doing something phenomenally stupid, but I'm evidently overlooking it.
Here's a collection of curves I've just plotted based on several experiments:
In terms of chemistry, I mixed up three small batches of the New Cyanotype chemistry, and all produce the same results, so it's not a mixing error - or at least not a spurious one. My approach is based on Mike Ware's notes here: https://www.mikeware.co.uk/mikeware/New_Cyanotype_Process.html
* to 2g potassium ferricyanide I add as much hot water to allow it to dissolve (2-3ml), and keep warm in a hot water jacket.
* to 6g ferric ammonium oxalate, I add 6ml hot water and dissolve
* mix together both solutions while still hot
* allow to cool down gradually
* filter the liquid and discard the crystallized out emerald green potassium iron oxalate.
The filtrate ends up being about the volume that Ware recommends, so I didn't add additional water to the stock.
I did not add dichromate, citric acid, a wetting agent or anything else to the stock solution.
I coat with a brush at about 0.5ml for a 5x7" area. I've used several papers (see chart above) without prior treatment. Coated paper is dried with a hairdryer and exposed immediately, and processed immediately after exposure.
Exposure is done with 365nm + 395nm LEDs, but I've also done a test with UV-BL tubes, producing pretty much the same H/D curve for all intents and purposes.
I've tried diluting the stock solution with water, which seems to increase printing speed (consistent with Ware's notes) and reduced dmax, but otherwise no apparent difference in curve shape/length.
I've tried adding a pinch of citric acid to the first wash bath or straight tap water, but see not difference; the prints clear in the same way.
I've tried getting the blue to develop with hydrogen peroxide vs. air-dried/naturally developed blue, and the end result is indistinguishable.
The different papers I've tested produce some differences in dmax, but curve shape is overall similar. The sagging pattern at the shoulder of some of the curves above is probably due to mottling which some papers are prone to; esp. the Schut Laurier paper tends to give some lighter blotches in the darker areas.
The somewhat long toe in some of the prints (e.g. the "Simili Japon #2" plot above) is probably due to incomplete clearing. I limited wash times to avoid bleaching as a result of the slight alkalinity of our moderately hard tap water.
I have also tried adding citric acid to the sensitizer prior to coating. In large quantities, this produced some instant fogging upon drying the paper, but this was below the dmin threshold and washed out in processing entirely. In smaller quantities, there was no apparent effect on the printing qualities or curve.
It's kind of puzzling, since Ware notes an exposure range of around 1.8logE for a full tonal scale print, and I get a full range from dmin to dmax on the paper with only around 0.6logE exposure range. In fact, the curve I get with the New chemistry is steeper than with Classic!
I'm sure I must be doing something phenomenally stupid, but I'm evidently overlooking it.
