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Thanks for your responses… the detective work continues.
Peter Friedrichsen: the splotches are clearly visible after exposure— before processing. The splotches are less dense (i.e. lighter).
Mark Nelson: I live between Boston, Massachusetts and Providence, Rhode Island. This time of year my darkroom is consistently cool —55 degrees F/ 15 C. Outside it’s usually within a few degrees of freezing and, when below freezing especially, very dry. I’m running a humidifier in my basement darkroom; my dehumidifier indicates humidity between 40% and 55%, but perhaps it’s drier above knee level.
Mike Ware: ‘fibrous, woolly, or cloudy” matches my spots exactly. This makes me wonder if my current roll of HPR is bad, since I haven't had the spotty problem in the past. After reading your pdf on paper blotching, I think I should try adding ammonium nitrate to my ‘New' Cyanotype. I don’t recall splotches on ’Simple’ Cyanotype. I haven’t used ‘Classic’ for some time because I’d been getting better results with ’New’ ( I’m wishing you at least another 25 years to continue the battles over paper quality).
Chris Anderson: I have been following your liturgy as religiously as possible for some time— prehumidification, hanging to dry, etc, as described (thank you, your book is wonderful. ☺️). I have been following all of your recommendations except one — combining CC & NC. If this is possible issue, I’ll give it a try.
It seems that I should continue with standard practices of prehumidification, hanging to dry, etc. but testing Mike’s ammonium nitrate add-in and Chris’s combination of CC & NC. Thanks again, everyone, for your alacrity and expertise.
On Feb 17, 2021, at 7:49 AM, Mike Ware <mike@...
Siderotype processes using ammonium ferric oxalate as the sensitizer, such as New Cyanotype, New Chrysotype, and Malde-Ware platinum-palladium, are reported -on occasion- to show a defect called “blotching or splotching”, in which irregular pale patches give a “fibrous, woolly, or cloudy” appearance to the image pigment. This is not due to crystallization, but is attributable to some non-uniformity in the paper sheet being disclosed and visually amplified by the sensitive photochemistry of these printing-out processes, which give very fine tonal separation.
In paper manufacturing today it has become almost universal practice to add so-called “retention aids” to the pulp at the wet end of the mill. These additives are likely to cause image “blotching” because they are highly polymeric organic polyelectrolytes, such as cationic polyacrylamides (CPAM), or cationic starch: they consist of long polymer chains bearing many positively-charged groups that will exert a strong attraction on the small, mobile, negatively-charged anions present in ammonium ferric oxalate photochemistry. These anions are liable to be trapped and rendered less reactive by local, non-uniform concentrations of the huge cationic polymer retention aid, thus wreaking havoc with our sensitive printed-out images.
Retention aids will interact much less with the sensitizers of traditional development siderotypes, like ferric oxalate or ferric ammonium citrate, whose larger molecules carry little ionic charge; this explains why the historic formulae like Classic Cyanotype and development Platinotype don’t suffer from blotching.
Although the makers of papers for siderotype now publicise the importance of excluding alkaline buffers like chalk from their product, they do not tell us whether they still include retention aids. It would be useful to know this. The handmade ‘Buxton’ paper that I commissioned from Ruscombe Mill in 1992 (specifically without chalk or retention aids) was used for 20 years with my ammonium ferric oxalate processes without ever showing a trace of blotching.
For anyone interested, I’ll attach a 4-page pdf which sets out the arguments in detail.
OK, cyano-peeps… I’m at my wits end.
I’m getting persistent spots, roughly 1/2 an inch in diameter, in spite of what I understand to be the usual precautions.
- I’m printing ‘New’ cyanotype on HPR; to the sensitizer I add 40% citric acid at 1:20 and 5% Tween at 1:30.
- I’m prehumidifying for 24 hours— paper placed on nylon screen with polyethylene cover over water (which tests neutral pH).
- immediately after sensitizing I hang the paper vertically for drying. I place a large tray with warm water on the floor immediately below the print to increase local humidity in case the sensitizer is drying too quickly. It’s taking less than an hour to dry.
- the darkroom temperature is 59 degrees F; humidity is at 56%.
- the spots are visible after exposure and before immersion in the first bath (1% sulfumic acid). The spots have no relation to the negative or printing frame.
- Now, it’s true that I’m not getting spots in the summer with this protocol, even if the dehumidifier indicates 40%.
Any suggestions would be greatly appreciated!
Thanks, Chris Seiberling