Re: Chemist question for all of you who love to figure things out

> For geleral image bleach, my favorite of slow working gentle bleach is
> an ammonium thiosulfate solution containing sodium metabisulfite,
> citric acid and disodium EDTA. This is a lot slower than dilute
> ferricyanide bleach but it's the best when brightening silver gelatin
> prints.

Of course that's actually a fixing/bleaching solution ("BLIX")...

Martin

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, June 02, 2005 5:11 PM
Subject: Re: Chemist question for all of you who love to figure things out

> Potassium cyanide is a very strong silver complexing agent and als is
> an agent very capable of fixing even silver iodide. In the context you
> cited, it might also have the function of a bleach.
>
> Silver iodide is hard to fix with thiosulfate fixer. There are several
> well known compounds that scavenge iodide ions, and those might work
> if added to an ammonium thiosulfate fixer. (On a different aspect of
> those compounds, they are used in some emulsions, like those used for
> medical films, as a blue-black agent because they can make the image
> very cold tone when added to emulsion. Unlike benzotriazole or other
> antifoggants they don't lose speed or slow development process.)
>
> For geleral image bleach, my favorite of slow working gentle bleach is
> an ammonium thiosulfate solution containing sodium metabisulfite,
> citric acid and disodium EDTA. This is a lot slower than dilute
> ferricyanide bleach but it's the best when brightening silver gelatin
> prints.
>
> --
> Ryuji Suzuki
> "Well, believing is all right, just don't let the wrong people know
> what it's all about." (Bob Dylan, Need a Woman, 1982)
>
>
> From: Christopher Lovenguth <chris@chrisportfolio.com>
> Subject: Chemist question for all of you who love to figure things out
> Date: Thu, 02 Jun 2005 00:47:34 -0400
>
> > I've come across something recently about "brightening" highlights of a
> > daguerreotype plate.
> >
> > Here is the text:
> >
> > "The daguerreotypist sometimes immersed the plates in a solution of
> > potassium carbonate and potassium cyanide with "a little alum, borax and
> > some other things" (Rinhart and Rinhart 1981
> > <http://aic.stanford.edu/jaic/articles/jaic35-01-002_appx.html> , 188).
This
> > procedure may have brightened the highlights by slightly etching them."
> >
> > Can anyone tell me what chemical reaction is going on here in a way
someone
> > who doesn't really know chemistry would understand. Also does anyone
have an
> > idea of what not so dangerous and toxic chemicals could be used to maybe
> > recreate the same reaction?
> >
> > Christopher Lovenguth
> > www.christopherlovenguth.com <http://www.christopherlovenguth.com/>
> > 917.721.4768
> >
Received on Thu Jun 2 21:30:55 2005