Re: APIS, hydroquinone hardening

Martin,

Thanks for the caution.

> From: MARTINM <martinm@SoftHome.net>
> Reply-To: alt-photo-process-l@skyway.usask.ca
> Date: Thu, 14 Jul 2005 12:20:07 +0200
> To: alt-photo-process-l@skyway.usask.ca
> Subject: 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 09:07:08 2005