RE: Calling LIAM RE: update on lumen prints

Hi Judy,

Sorry for delay - I'm just back from a few days away. I think you're
probably thinking of the reversal bleaches, which remove silver but leave
the halides behind (for treatment with dev or toner). These (or at least
the ones I used) are made with either pot. dicromate or pot. permanganate
with sulphuric acid, but I don't think either is any use here (what exactly
is a lumen print, anyway??)

Re. George's question, iodide "fixation" won't give an archival result, but
Mike Ware's book does talk about redeveloping faded prints. It says:

"The light-induced bleaching of silver in the presence of iodide, which
Talbot made use of in his leucotype process, has not been explained. Free
iodide ion only absorbs in the ultraviolet (at 226 and 193 nm), quite beyond
the spectrum of the incident light [he's talking about fading under gallery
illumination], so this cannot be the direct cause. It is certain that the
silver metal will have a surface layer of chemisorbed silver iodide, which
does absorb in the near UV and blue regions, and it may be a photo-electric
effect within this semiconductor surface layer that provides the mobile
electron/hole pair needed to promote the redox reaction above.

"Because the redox potential of the silver/iodide couple is not too
negative, iodide-bleached silver images can be redeveloped by the action of
conventional photographic developers, which are mild organic reducing
agents. Talbot himself made use of this to 'revive' faded calotypes using
his 'gallo-nitrate of silver' solution."

Liam

-----Original Message-----
From: Ryuji Suzuki [mailto:rs@silvergrain.org]
Sent: 16 September 2005 17:16
To: alt-photo-process-l@sask.usask.ca
Subject: Re: Calling LIAM RE: update on lumen prints

From: Judy Seigel <jseigel@panix.com>
Subject: Calling LIAM RE: update on lumen prints
Date: Thu, 15 Sep 2005 22:19:07 -0400 (EDT)

> There's a bleach that removes ONLY the silver halide -- that is, the part
> that's not yet developed to metallic silver, which is why you have to fix
> in the 1st place.

Bleach is usually a solution that removes metallic silver, not silver
halide. Some bleach dissolves metallic silver into the solution, while
others oxidize metallic silver to silver halide. Fix is the solution
that removes silver halide.

To go back to the original question, fix is necessary for long term
stability. This is regardless of whether the image part is toned with
noble metal or not. If silver halide is not removed, they can easily
get converted to silver sulfide by environmental pollutants, or even
reduced to metallic silver over time. Both cases the result will
appear as severe image stain.

> If memory serves (which it may not) that's a potassium
> ferricyanide with potassium bromide and --- hydrochloric acid? I have it
> somewhere, but LIAM will know... LIAM! Calling LIAM !

It is very dangeours to mix ferricyanide with mineral acids. This is
a known way to liberate cyanide gas by decomposing ferricyanide.

Either way, using ferricyanide bleach in the original context would
remove image but not the unexposed silver halide.
Received on Fri Sep 16 11:31:07 2005