Re: Persistent cyanotype spots


Cinda Berry
 

Hi Christina,

Just wanted to say that I have your book and it is an indispensable resource.  

It is written so well and has so much good information that I was able to get some decent cyanotypes on the first try!

Cinda


On Feb 16, 2021, at 9:18 PM, Chris Seiberling, <christopher.seiberling@...> wrote:

 HPR — Hahnemühle Platinum Rag.

On Feb 16, 2021, at 7:18 PM, ender100 via groups.io <Ender100@...> wrote:

What paper?

Best Wishes,
Mark Nelson


Curve Calculator III for the Mac is Now Available

sent from my iPhonetypeDeviceThingy

On Feb 16, 2021, at 6:15 PM, Chris Seiberling, <christopher.seiberling@...> wrote:


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



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