I'm fogging my cyanotype paper. An example is attached. Note the fogging that seems to follow my brushing. This was after a day of drying in a somewhat humid environment (the cabinet under my bathroom sink.) Traditional cyanotype with dichromate added, Arches Platine paper, two coats.

My only thoughts at this point are possible contamination from the brush or from letting the solution sit an hour between coats.
Any ideas or suggestions? Thanks!

I had the same problem and it was due to contamination on the surface I used to coat the paper on. I used the top of my tray heater which had fixer and developer spills on it. A good wipe-down soon fixed it. The tray heater then dried the paper for me and I found this helped too - the quicker I get the paper into an old paper box the better.

Barry

I think it might also just be uneven coating. I have been using fixed, old, fibre photographic paper and the glossy emulsion coated surface means the potion runs and 'pools' as it dries, leaving dark green patches. I have found that this can be mitigated by draining off any excess potion and then periodically re-brushing with a 'dry' brush as the paper dries.

Crispin

Athanasius,

Double coating is a PIA with Cyanotype. You have to adjust the amount of sensitizer very carefully; not too much and not too little - just right! You should not let the sensitizer pool on the paper and you also shouldn't overbrush. Double coating is usually hit and miss -> I never managed to get 100% success when double coating Classic Cyanotype; 66% (2/3) at max.

* Use a little surfactant (Tween, Ilfotol, Photo-flo) to facilitate absorption.
* Dry the paper thoroughly (you can use a hair dryer, but waiting for at least 5-10 minutes after coating) before coating the second time
* Do not overbrush and let the sensitizer crystallize over the paper in the second pass
* Always keep the paper in a very dry environment -> double coated paper fogs much more easily

and

* If you really need high dmax, make yourself a favor and switch to New Cyanotype.

Hope this helps,
Loris.

I'm fogging my cyanotype paper. An example is attached. Note the fogging that seems to follow my brushing. This was after a day of drying in a somewhat humid environment (the cabinet under my bathroom sink.) Traditional cyanotype with dichromate added, Arches Platine paper, two coats.

My only thoughts at this point are possible contamination from the brush or from letting the solution sit an hour between coats.
Any ideas or suggestions? Thanks!

Eliminate the dichrmate from the formula and see if that solves the fogging problem.

I've only seen this sort of fogging after coated paper was left for days before exposure. I always double-coat.

Perhaps this paper needs an acid treatment before coating with the cyanotype emulsion. Try some cheap non-buffered (not acid-free) paper. Print on a paper lunchbag and see if the emulsion fogs it. Or try some Cranes' Kid Finish Stationery. The latter is a good paper for many alternative processes including cyanotype.

Joe