RE: APIS, hydroquinone hardening

Chris (and others), since we are already coating with a mix of
gum/dichromate, don't you think it would be sufficient to just coat with
unhardened gelatine + hydroquinone, then let the dichromate in the
emulsion do the hardening? Just a thought...in theory I don't see why it
wouldn't work.......unfoirtunately I'm in a writint phase right now and
have scads of hardened paper sitting by, so don't have time to test this
out myself.
Kate

-----Original Message-----
From: Christina Z. Anderson [mailto:zphoto@montana.net]
Sent: Thursday, 14 July 2005 10:58 a.m.
To: alt-photo-process-l@sask.usask.ca
Subject: Re: APIS, hydroquinone hardening

Thanks, Jack, for the more complete explanation. I was too busy with my
brain wheels turning about a possible gum size to take complete notes on
his processes.

The reason for the interest to those not present at APIS: at the
moment, we have glut, gly and formaldehyde for hardening a gelatin size.
All have questionable toxicity for some people. I personally love
glutaraldehyde if I can ever spell it correctly, and use that in my
practice, and I agree with Ryuji's comments, below. Clay H. has given
up glyoxal and gone to chrome alum. Sandy King uses chrome alum.
Katharine, Sam, and others don't size.

Paul's system (having NOTHING to do with a possible size, but part of
his carbon-q process if I remember correctly) is having a 1%-3% amount
of dichromate in the gelatin already, and the hydroquinone amount is so
small (if I remember, 0.5%) that my idea would be to size the paper in a
tray of the di/gelatin, and then pass it thru a bath of the hydroquinone
(Paul had added a pinch of hydroquinone to the gelatin/di mix and voila,
instant hard, which is why I thought to try the bath of hydroquinone).
The miniscule amount of dichromate left after the baths should not be a
problem but heck, until I test it out who knows if it does or doesn't
work. I hope others will try it. Maybe it is a bust. BUT, presuming
in a class of students where you are already teaching gum printing with
dichromate, the use of di and a pinch of hydroquinone would seem to be
less toxic than other choices...perhaps.

As always, theorizing is one thing, trying it out is another. I plan on
trying it out and hope others will, too. I'm not sure how I will try
it, how I will combine it, but I will stick to the proportions that Paul
shared because at this point that is all I have to go on. Like testing
to see if boiled gelatin ruins a size, all you gotta do is boil some
gelatin and find out (which I did, and it doesn't). Chris
> From: Jack Brubaker <jack@jackbrubaker.com>
> Subject: Re: APIS, hydroquinone hardening
> Date: Wed, 13 Jul 2005 14:58:35 -0500
>
> > As a fellow gum printer who doesn't feel I have found the Holy Grail

> > of sizing options I to was excited about this idea. Paul found that
> > a
gelatin
> > coating that contained a small amount of hydroquinone could be
> > hardened
by
> > the addition of a small amount of dichromate.
>
> Ryuji says: This can work, but the net effect should be similar to
addition of
> chrome alum. Presence of oxidized hydroquinone in absence of sulfite
> may also help to form a different kind of crosslinking. But personally

> I don't see why one might want to use more than one step of work for
> the hardening process when one is enough. Addition of a very small
> amount of glutaraldehyde immediately before coating works as good as
> anything else I tried and it is by far the easiest hardening process I

> know of.
>
> > The dichromate could be either brushed on and then washed off once
> > the reaction had occurred or perhaps the usual gum coating could be
> > brushed on and the sizing under it would be "set" by the dichromate
> > in that first layer of gum.
>
> If you do the latter, I would expect the "fog" level to rise.
>

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