Re: Glycerol as humectant for POP Pd prints at low RH
----- Original Message ----- From: "Loris Medici" <mail@loris.medici.name> To: <alt-photo-process-l@usask.ca> Sent: Sunday, February 25, 2007 10:18 PM Subject: Glycerol as humectant for POP Pd prints at low RH > Hi all, > > Probably I'm not the only smart person to tried this before but since > I haven't found a reference in the list archives, I decided to share: > > I was having hard time making cold/neutral toned POP Pd prints lately; > the RH of my darkroom changes around 25-30% and printing w/o drying > thoroughly (in other words: with almost wet paper) isn't a good choice > since I'm using a relatively weak digital negative substrate and > printing on almost-wet paper = ruining the negative due excess > humidity. (The negative substrate I use is Ultrafine Crystal Clear.) I > also don't prefer to use a thin (1-3 mils) polyester sheet between the > negative and the paper because sharpness will suffer... (I'm printing > using a 11x14" contact printing frame and a bank of BL tubes.) > > Anyway, given the above criteria, I decided to put glycerol > (glycerine) into my coating solution. Since this compound is used as a > humectant in both carbon printing (tissue will retain humidity when > some glycerol is present and won't brittle) and silver-gelatine > emulsion making, I thought it may help me in retain humidity in the > paper -> letting me get cold/neutral tones. > > It works! I added a drop of glycerol per 10 drops of coating solution, > dried the paper for 10 minutes and got a neutral print. Without the > glycerol - keeping all other parameters constant - I would get a warm > (brown) print. > > Do you think adding glycerol will affect longevity? I'm using very > little... (0.1ml per 1ml coating solution) > > Regards, > Loris. In the context of DCG (gelatin) adding glycerol is said to speed up dichromate reduction. Hence it will accelerate dark reaction. Martin
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