Re: APIS, hydroquinone hardening

From: Paul Lehman ^lt;[email protected]>
Date: 07/14/05-09:20:16 PM Z
Message-id: <20050715032016.62329.qmail@web50911.mail.yahoo.com>

Hi Christina:

It was truly a pleasure meeting you at APIS. I am just
now able to catch up on my emails and was quite
surprised at the number of comments on the potential
for using hydroquinone for hardening gelatin and gum.

Although I can't go through each individual email, nor
can I directly recall all the comments, here are a few
observations related to the topic:

A description of the actual print process mentioned
can be found in the Post-Factory Photography Journal,
Vol 9, page 22, as the Carbon-Q process. It is a
cousin to the ozotype process which has been indicated
by some (in the old literature) to also use
hydroquinone. For those who may like a copy of this
article, please email me directly (off list) and I'll
scan in an electronic copy (I have permission to share
by the editor of the Journal; however I do recommend
purchasing your own copy directly as the first option
to consider, if they are still available). I also left
a copy of my PowerPoint presentation with Dick
Sullivan, who said that the APIS presentation will
eventually be posted on the B&S site (but do be
patient as I know that Dick is involved in a million
things right now).

I can not vouch to say that it will be a good sizing
process, but I would think it could well work as such.

I wouldn't worry about the "rubber" description of the
outcome as that was observed in a 200 mL volume. I
suspect that the usual hardening methods would produce
the same outcome if performed in a beaker at that
volume. The final print (using this process) results
in a normal appearing coating that has no unusual
tactile feel.

The concentrations used in the print process were
designed for the print, you may need to experiment to
optimize for a sizing approach. My first guess would
be that you can get by with less bichromate (start at
0.5% -1%) with the hydroquinone at 0.5%. I would
suggest you try it first in a small container
(disposable of course) by melting the gelatine (or
gum), add the bichromate to dissolve, then add the
hydroquinone (which could be pre-dissolved in a small
volume of water, or added directly). Mix and see what
happens. This would save you paper and larger volumes
for the initial tries. When you find the minimum
necessary concentrations, then try those
concentrations on paper.

I only tried it once with gum arabic, in a disposable
beaker. I recall that the reaction was slower than
observed with gelatin, but it did occur (possibly
because the gelatin was a hot solution whereas the gum
was at room temperature).

Hydroquinone, when standing in solution, will slowly,
by itself, decompose to benzoquinone with air
exposure. I suspect that the conversion to
benzoquinone may be part of the reaction with
bichromate, but have no empirical proof. However, be
aware that benzoquinone is a brown colored chemical.
Just be sure to rinse your prints well to remove
residual Hydro- or benzoquinone. In the few prints I
have made with this process, after about 5 years now,
there is NO evidence of any discoloration, so this may
not be of any issue or concern.

As to the safety issues related to hydroquinone, ALL
chemicals have a degree of risk, especially chemicals
used in alternative processess. However, hydroquinone
is sold over-the-counter as a topical skin lightening
agent (2% concentration), and as a topical
prescription at higher concentrations (4%). Trace
amounts of benzoquinone form in the topical
formulations over time. I would consider it much safer
than the dichromates used in alt processes, which are
sloshed about all over the place. As I tell my lab
crew: "don't eat it, don't drink it, and don't poke it
into your eye" (and wear gloves at all times), and as
such, there should not be any significant safety issue
with these extremely low concentrations of
hydroquinone being discussed here.

When you do try it on paper, try coating the paper
with the gum and dichromate, let partially or fully
dry, then paint on the hydroquinone solution, wait 10
or 15 minutes to react (guessing), then rinse all
until clear. Alternatively switch the dichromate with
the hydroquinone, coat, dry, paint with the
dichromate, wait to react, then rinse. Either way may
work.

O, and the job title your where trying to recall was
"dermatopharmacokineticist" (they pay higher salaries
when you have longer job title).

I too will do some home experimenting to see if this
approach can be used as a sizing, but unfortunately it
will need to wait for a couple weeks as I'm out of
town again next week.

Cheers all,

Paul A. Lehman

  

--- "Christina Z. Anderson" <zphoto@montana.net>
wrote:

> Martin and Ryuji,
>
> Hmmm....food for thought.
>
> Martin, so our silver developers that contain
> hydroquinone harden the
> cornea? Bummer...is there no safe hardening agent
> out there? How about
> chrome alum?
>
> Ryuji, re: fog, if it completely hardens the gum
> layer applied then it would
> be useless, but if it just hardens a bit of the
> layer that is in contact
> with the paper, then that could just be developed
> out. That's one thing gum
> has going for it--it is not a one shot deal. There
> are always variables
> along the way. The only way I'll be able to find
> out is when my
> hydroquinone order arrives from B and S. But your
> point about glut
> hardening slowly and not instantly is an important
> one.
> Chris
>
> ----- Original Message -----
> From: "Ryuji Suzuki" <rs@silvergrain.org>
> > Although I agree that hydroquinone should be
> supplied after
> > dichromated gelatin is coated to go around rapid
> reaction between
> > them, I don't think immersion is a good idea.
> Immersed paper would
> > contain excess hydroquinone, and unless you remove
> this, it can cause
> > elevated fog with dichromated gum process (and it
> can completely fog
> > silver gelatin process). You could reverse this
> and coat hydroquinone
> > and bathe in dichromate, but that would produce a
> lot of waste
> > chemical containing chromium (bad for
> environment).
> > If you take this approach, my preferred strategy
> would be to find a
> > compatible reducing agent for dichromate, but one
> that reacts only
> > very slowly. This way, you can mix gelatin, water,
> dichromate and
> > reducing agent in one coating solution and coat.
> Sized paper will be
> > hardened by the time it is fully dried.
> > My conclusion: glutaraldehyde.
>
>
>

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Received on Thu Jul 14 21:20:29 2005

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