Re: Sources for wet plate collodion chemicals

----- Original Message -----
From: "Etienne Garbaux" <photographeur@softhome.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Sunday, August 28, 2005 4:19 PM
Subject: Re: Sources for wet plate collodion chemicals

> Richard wrote:
>
>> Ammonium thiosulfate is a better fixer for Silver Iodide,
>> is it not
>> good enough for wet plate? Secondly, I am puzzled by the
>> term
>> "brightening", does this refer to the negative or the
>> print? Is it
>> actually another term for contrast[?]
>>
>> Cyanide is a solvent for metallic silver so, it seems to
>> me, that
>> excessive fixing in it would destroy part of the very
>> fine grain wet
>> plate image. Is this slight reduction what is being
>> referred to, and
>> if so, it is considered desirable or undesirable?
>
> The collodion coating, even when still wet, is only
> semi-permeable to
> water. Thus, diffusion into and out of the collodion is
> very limited
> and the most aggressive agents available are generally
> employed.
>
> "Brightening" is the term used for methods that create a
> whiter-looking
> silver deposit, which is desirable when the image is a
> positive (i.e.,
> tintype, ambrotype, and daguerrotype). As you know, modern
> silver-gelatin materials tend to produce large "fuzzballs"
> of silver
> filaments that absorb light and look black. The positive
> silver
> processes depend on much smaller, reflective deposits of
> silver that
> look whitish. Brightening accentuates this effect.
>
> Best regards,
>
> etienne
>
   Thanks for the detailed answer, It explains what was
puzzling me.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com