Re: APIS, hydroquinone hardening

> he discovered that
> (Katharine Thayer, this might interest you!!) gelatin with a touch of
> dichromate and then a pinch of hydroquinone instantly hardens into a
rubbery
> mess. He talked about crosslinking of gelatin and gum, and the light bulb
> went off in my head about a new possible way of sizing with less toxic
> stuff.

I believe what's actually taking place here, is the Hydroquinone (Quinol) is
oxidized by the dichromate to form Parabenzoquinone (PBQ alias Quinone).
PBQ is a well-known organic hardening/bleaching agent used for silver halide
emulsions.
However, there are considerable toxic hazards associated with PBQ: e.g. it's
notorious for causing cornea damage.
By the way, you may get similar hardening action from oxidizing Metol
instead of Hydroquinone.

Martin

----- Original Message -----
From: "Jack Brubaker" <jack@jackbrubaker.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Wednesday, July 13, 2005 9:58 PM
Subject: Re: APIS, hydroquinone hardening

>
>
> Christina mentioned in reference to Paul Lehman...
>
> >he discovered that
> > (Katharine Thayer, this might interest you!!) gelatin with a touch of
> > dichromate and then a pinch of hydroquinone instantly hardens into a
rubbery
> > mess. He talked about crosslinking of gelatin and gum, and the light
bulb
> > went off in my head about a new possible way of sizing with less toxic
> > stuff.
>
> 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. The two ingredients can't be
> mixed together in the gelatin because the reaction between them will go
off
> almost instantly. He commented he has two beakers of "rubber" created by
> mixing hydroquinone and dichromate in gelatin. Within 30 seconds he said
the
> solution went from liquid to solid, trapping the stirring tool he was
using.
>
> He has made prints by a very clever "wet carbon" process where he uses
this
> reaction to selectively solidify carbon tissue (that contains
hydroquinone)
> still damp from coating by placing it in contact with a paper final paper
> support that has an exposed dichromate image (dichromate only). The
> unexposed and therefore unconverted dichromate bleeds into the carbon
tissue
> and interacts with the hydroquinone to harden the gelatin. The image bonds
> onto the dichromated support and is developed as in traditional carbon
> transfer. The forgoing is a very brief and I hope not misleading account
of
> the process as I recall it. He had prints he had made by this process that
> showed promise. He had so much to say and covered it so quickly that I
> couldn't make meaningful notes so the above is from memory. I hope Paul
will
> write up a more complete and accurate account for us all... He had
"slides"
> in his PowerPoint that detailed the formulas he has used, but I was so
> engrossed in being sure I understood him that at the rate he moved through
> his information I didn't get it all written down. Sullivan mentioned he
> hoped to post all the presenters visuals on his site in the near future.
>
> But to return to my topic, using this hardening effect as a gum size. I
> don't have the materials yet but plan on trying applying a gelatin and
> hydroquinone size that would be hardened by subsequent application of a
> dichromate. 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. The appeal to me is that the reaction is very quick,
it
> is powerful, and the hydroquinone is non-threatening for skin contact (an
> active ingredient in age spot removers). Paul said that although one
> wouldn't want to ingest the stuff it is quite safe. A far cry from most of
> the hardeners now in use.
>
> Jack
>
Received on Thu Jul 14 04:17:27 2005