[alt-photo] Re: tintype

[Richard Knoppow]

----- Original Message ----- 
From: "Vedos" <vedos at samk.fi>
To: "The alternative photographic processes mailing list" 
<alt-photo-process-list at lists.altphotolist.org>
Sent: Saturday, November 06, 2010 1:29 PM
Subject: [alt-photo] Re: tintype


> How will it be known if the cyanide did the job then, 
> until we are long dead? Actually, with cyanide we can 
> easily be soon dead! We do wpc with students, but never 
> think of using potassium cyanide in these conditions!
>
> The fixing has been done both with cyanide and hypo from 
> the beginning... here's what John Towler recommends in his 
> "Silver Sunbeam", from 1864, chapter 17:
>
> "Cyanide of potassium is not only a solvent of the silver 
> salts above mentioned, but also a reducing agent; it thus 
> produces in the ambrotype and the melainotype a whiteness 
> in the silver film which can not be effected with 
> hyposulphite of silver. For this reason it is regarded by 
> many photographers as the fixing agent peculiarly adapted 
> for collodion positives by reflected light; whereas in the 
> negative, where the whiteness of the silver film is of 
> little or no consequence, hyposulphite of soda is regarded 
> as the proper fixer. Many photographers disregard these 
> refined distinctions, and use, in consequence of the 
> superior solvent properties of cyanide of potassium, this 
> substance as a fixing agent indifferently for negatives 
> and positives. But because cyanide of potassium dissolves 
> the silver salts so easily, it has to be used in a dilute 
> condition, and to be watched very closely, otherwise it 
> will dissolve at the same time the fine parts of the 
> image."
>
> Best regards,
> Jalo
>
   For gelatin emulsion the degree of fixing is easy to 
determine by the use of a test solution of either sodium 
sulfide or Kodak Rapid Selenium Toner. They would probably 
also work on a collodion negative or ambrotype print. Unless 
the dried collodion is _so_ impermeable that no soltion of 
any sort can penetrate it. I wonder about that because even 
cellulose nitrate and cellulose acetate film support swell 
in water a little during processing and then shrink when 
dry. That's why motion picture film came in two perforation 
pitches, i.e., so that raw stock would match the processed 
negative when printing.
    I did do some searching for articles on the archival 
processing of wet plate negatives but could find nothing 
specific. There is quite a bit on preservation of 
ambrotypes, which are evidently quite vulnerable to chemical 
attack but I am not at all sure if this applies to collodion 
on glass. I don't know if Ryuji Suzuki still follows this 
list but he might have authoritative information.
     AFAIK the use of potassium cyanide as a fixer continued 
only because the use of thiosulfate was not well known.
     BTW, it appears that the collodion sensitive layer, and 
indeed cellulose nitrate and acetate support are actual 
emulsions where the gelatin sensitive layer is a suspension 
and not an emulsion. I remember attending a technical paper 
given by Technicolor many years ago where the speaker kept 
referring to the "emulsion". He confused everyone because he 
was talking about the _support_ not the sensitive layer. 
Someone finally managed to get him to clarify that.
    The term "emulsion" has become so well established for 
the gelatin sensitive layer that the practice will never 
change.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk at ix.netcom.com