Correction: Third (last) Link (4% Gelatin) should be https://illumina-chemie.de/viewtopic.php?p=72823#p72823

Udo

-----altphotolist@groups.io schrieb: -----
An: altphotolist@groups.io
Von: "BJ68,"
Gesendet von: altphotolist@groups.io
Datum: 18.02.2021 09:04
Betreff: Antwort: Re: [altphotolist] Persistent cyanotype spots

a) Ammonium nitrate is a restricted substance at least in the EU see Annex I in https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32019R1148&;from=EN and even if you are a professional user (in German "Gewerblich") it can be difficulty to obtain a small amount.

b) Other suggestions:

1. Adding gelatin and glutaraldehyde to your cyanotype chemistry see https://illumina-chemie.de/viewtopic.php?p=72786#p72786 (in English) 6% are to much (emulsion is to viscous) so I cut it to 4% see https://illumina-chemie.de/viewtopic.php?p=72786#p72786 (in German only). Mixtures are stable for more than 1.5 years @ RT (room temperature) see https://illumina-chemie.de/viewtopic.php?p=78036#p78036
Modification would be to take only the gelatin and reduce the amount to 1 to 2% @ the potassium ferricyanide solution. Should gave you a additional layer with will stain your spots.....

2. Not tested: To replace the gelatin from recipe above with polyvinyl alcohol or polyvinyl acetate, which will make the same...adding a layer where the formed pigment will be withhold, covering the areas of the spots after development.

Udo