U of S | Mailing List Archive | alt-photo-process-l | Re: gum preservatves

Re: gum preservatves

Whatever the case that is going on, I found the acidity to cause problems, and when Demachy and Maskell came out with this "acid gum" process in the very beginning, in the first book they wrote, I never saw it used by him/them afterwards so it must not have been effective in the long run. It was the proverbial flash in the pan or one-hit wonder. I'm not particularly interested in testing it because I don't find a need to use acidity in any way myself.

Christina Z. Anderson
----- Original Message ----- From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@usask.ca>
Sent: Thursday, September 04, 2008 7:56 PM
Subject: Re: gum preservatves

You might want to be a bit careful here. Lemon juice is not
just acid, but it has some reducing properties that can
interact with dichromate. Although less reducing power, citric
acid may also be oxidized by dichromate more easily than gum
molecules. Some other acids, especially mineral acids, have
less reducing, but rather more oxidizing properties. Also,
citric acid and many organic acids have affinity to form
chromium (III) complex ions. I would not attribute your
observation (and also what's described in your quote from
Demachy) to acidity (that is, the pH dependency) until
sufficient evidence is gathered to support such an idea. Also,
meanwhile, modifying your practice based on the assumption
that what's described is an acid effect may lead to a
confusing or inconclusive result.

Ryuji Suzuki
"Strange how people who suffer together have stronger connections
than people who are most content." (Bob Dylan, Brownsville Girl, 1986)

From: "zphoto@montana.net" <zphoto@montana.net>
Subject: Re: gum preservatves
Date: Thu, 04 Sep 2008 16:12:08 -0600

Demachy says:  &#8220;A strong proportion of citric acid or
a smaller proportion of more active acid added to the
mixture of gum and bichromate will utterly destroy its
sensitive properties; that is, will render it insoluble
without exposure to light to such an extent that repeated
friction with a sponge and hot water will scarcely affect
it.  We may, therefore, take advantage of this property to
counteract the excessive solubility of freshly prepared
paper and lessen exposure, giving more stability to the
half-tones.  A small quantity of a weak (say 5%) solution of
citric acid, or simply a few drops of lemon juice added to
the sensitive mixture, will start insolubilization and allow
of slower and surer development.  It is better, however, to
master the ordinary process before resorting to this
expedient.&#8221;  39

Have at it, Loris.  I found that the more lemon juice drops
I added to the mix (with drops of water added to the control
group in the same proportion) that I got lots of staining of
the highlights and lower contrast, but with paper negs this
might be helpful to you--I mean, the lower contrast part.
Step wedge steps were not too differentiated.

----- Original Message Follows -----
From: Loris Medici <mail@loris.medici.name>
To: alt-photo-process-l@usask.ca
Subject: Re: gum preservatves
Date: Thu, 04 Sep 2008 21:37:54 +0300 (EEST)

>David & Chris, that also arrived to my mind just after had
>sent my last message... Even if I refrain to introduce
>another alien compound into consideration - as a first
>impression -, it sounds interesting / promising. You can
>bet I will try this (with citric acid)as soon as possible!
>Of course there's also the staining issue... I'll see.
>Chris, do you know how much lemon juice was Demachy adding
>to his gum?
>4 Eylül 2008, Perşembe, 8:28 pm tarihinde,
>> zphoto@montana.net yazmış: Lemon juice does the trick
>> was Demachy's method in 1897. Chris
>> ----- Original Message Follows -----
>> From: davidhatton@totalise.co.uk
>> To: alt-photo-process-l@usask.ca
>> Subject: Re: gum preservatves
>> Date: Thu, 04 Sep 2008 16:18:47 +0100
>>>Hi Loris,
>>>Is there any reason one can't add some acid to the mix,
>>>Oxalic or citric say, to give an increase in printing
>>>speed? You could have a non-smelling acidic mix then..

Assistant Professor of Photography
Photography Option Coordinator
Montana State University
College of Arts and Architecture
Department of Media and Theatre Arts, Room 220
P.O. Box 173350
Bozeman, MT 59717-3350
Tel (406) 994 6219