[pure-silver] Re: Paraformaldehyde/Acetone in lith developers
- From: "Tim Rudman" <tim@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 1 Mar 2010 11:42:13 -0000
Hi Robert
Because you guys are so far behind us - only in terms of time zones of
course :-) ! - your posts come in when I am asleep and have usually been
answered thoroughly by the time I wake up and eventually get to my computer.
As has been said, the formaldehyde or a replacement is indirectly required
in the explosive chain reaction of infectious development.
Infectious development can only take place in an environment of very low
free sulphite. Excessively low levels may give pepperdot and random
infectious development. Higher levels will stop infectious development
completely (see your M.P.Lith printing Course for more details Robert).
Lith developers are very prone to oxidise quickly. In high dilutions used by
some lith printers (me included) free sulphite levels become extremely low,
and what little there is present is quickly used up. Low sulphite levels
cause increased rate of oxidation. Formaldehyde bisulphite frequently is
used to restrain this. Free sulphite levels are kept low by combining with
formaldehyde, paraformaldehyde or acetone.
Some people dislike working with formaldehyde/paraformaldehyde because of
its odour and toxicity and so formaldehyde free developers are promoted by
some (eg Moersch). Acetone is often used for this substitution.
I have not made acetone substitution versions personally as the odour has
never bothered me, possibly because I mostly use high dilutions at room temp
or a bit higher. It is a bit more intrusive when I use high temperature lith
processing though but i think the odour is less than some stop and fixer
baths. I don't have worries about the possible toxicity either as dilutions
are so high and with sensible handling I believe risk to be negligible and
probably less than a drive through town. One should always be sensible when
handling any lab products and there really is little reason why theoretical
risk should turn into actual risk unless you allow it to. I recall a lab
finals exam at med school many years ago when everyone was given their own
petri dish with a bacterial growth on it (all different) and we have to each
run it through the necessary tests to identify what it was. I was quite
surprised when my tests showed me that I was handling live bubonic plague,
but it was also a timely reminder that risk can be controlled! I test lots
of things that I want to use but life is just too short to test all those
that I don't! You will find a contribution on experiments with homemade
formaldehyde-free lith devs with several formulae by Peter Svensson in the
'Forum' section of The World of Lith printing p.150, if that helps.
Best to Tiffany
Tim
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Robert Hall
Sent: 01 March 2010 00:35
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Paraformaldehyde/Acetone in lith developers
Fellow Silverados...
Does anyone know what the purpose of Paraformaldehyde is in lith developers?
If Acetone can be substituted, what is the ration of the substitution?
How does Acetone compare to Paraformaldehyde in the resulting print?
Thank you in advance.
Robert Hall
www.RobertHall.com
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 8.5.435 / Virus Database: 271.1.1/2707 - Release Date: 02/28/10
07:34:00
Other related posts:
