silver chloride paper/was RE update on lumen prints

On Thu, 8 Sep 2005, Liam Lawless wrote:

> 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??)

I'm wracking the memory, but pretty sure there was something else that I'm
not retrieving now... possibly related to the plating-out toner I did
after solarizing, so it was already a reversal. That was, however, 20
years ago, and stuff is stacked a mile high on top of it since then.

But speaking of the so-called "lumen" process now under discussion,
this did come back to mind:

I did it two ways, One was just to bleach a print with what was also
called a "Stain Reducing Bleach," which changed the bromide paper to a
silver chloride paper, which printed out in sunlight to a nice tactile
brown when untoned, other if toned I assume.

The other was simply to make a whole sheet of silver chloride paper out of
regular bromide paper by fogging then developing paper to be fully black
(metallic silver) then bleaching back with the SR #2 bleach until fully
"white" (silver chloride).

This then (according to OR Croy & also my limited tests) is re-sensitized
and can be re-exposed & toned as by Wm Henry Fox Talbot & company.

Somebody named Hugo or Humphrey something told me about this at a Lacock
Abby workshop, but his attitude was that *everybody* knows how you make
silver chloride paper & he was surprised I didn't.

The formula (from P-F #3, p. 28) is:

Dissolve 13 g potassium bichromate in 600 ml water, add 30 ml HCL, Bleach
print. Rinse in several changes of water, rinse in sodium sulfite solution
of about 1/4 tsp per 25O ml water, rinse a few times more (to clear the
bichromate stain). Redevelop print in paper developer or toner. Stock
solution keeps forever; working solution for several days. Am di is OK,
use slightly less, tho in bleaches measurements are rarely critical.

But if anyone reading this has P-F #3, I see I left something somewhat
unclear. In column #2 on page 28, I said "Change your modern bromide or
chlorobromide factory paper print to silver chloride..." etc. but SHOULD
have added "as in SR #2, above." Whoever has that issue, would you pencil
that note in & make me feel better?

thanks,

Judy

> 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
>
Received on Sun Sep 18 19:00:31 2005