RE: Glycerol as humectant for POP Pd prints at low RH

[Loris Medici <mail@loris.medici.name>]

Hi Bob,

I can't say that I know polyvinyl alcohol in depth, but I couldn't find
any data indicating it is commonly used as a humectant:

http://en.wikipedia.org/wiki/Humectant
http://en.wikipedia.org/wiki/Polyvinyl_alcohol

Regards,
Loris.

-----Original Message-----
From: BOB KISS [mailto:bobkiss@caribsurf.com] 
Sent: Monday, February 26, 2007 2:27 AM
To: alt-photo-process-l@usask.ca
Subject: RE: Glycerol as humectant for POP Pd prints at low RH


DEAR LORIS,
	I am just wondering if the polyvinyl alcohol that I add to my
DOP PT/PD coatings serves a similar purpose?  Of is it just to make
coating easier?
		CHEERS!
			BOB

-----Original Message-----
From: Loris Medici [mailto:mail@loris.medici.name] 
Sent: Sunday, February 25, 2007 5:18 PM
To: alt-photo-process-l@usask.ca
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.