[alt-photo] Re: tintype

[etienne garbaux]

Chris wrote:

>I have just received the bulk tintype developer from Rockland and 
>had a question.
>
>There are 3 parts:
>1. Dektol
>2. Bag of white powder (I think is sodium sulfate)
>3. Bottle of liquid which by the MSDSes is either ammonium 
>thiocyanate 50% or sodium thiosulfite 5%.
>
>The confusion comes with the labeling of 1. 2. 3. which seems to be 
>different with different kits...unless I am just accessing old files 
>on the web and I am the one confused.
>
>Anyone mix their own tintype/fogging I assume developer?

I have made real (wet-plate collodion) tintypes, but have no 
experience with the Rockland kit, which IIRC (and despite some of 
Rockland's claims) uses dry plates, made with pre-sensitized liquid 
gelatin emulsion -- not a wet-plate collodion emulsion that you 
sensitize with silver nitrate after coating.  This is corroborated by 
the Rockland web site, which indicates that its tintype fixer is 
Kodak Fixer.  For real collodion tintypes, you would need to use 
potassium cyanide.

While Rockland describes its tintype developer as a "reversal 
developer," tintypes and ambrotypes (like Daguerrotypes) do not 
actually use reversal processing in the traditional sense of the 
term.  The silver deposits remain negative (i.e., more silver where 
there was more exposure).  The apparent positive "reading" is caused 
by the black backing and by development that causes the silver 
deposits to look more whitish than the normal black silver deposits 
we are familiar with.  In the wet-plate collodion process, this is 
usually accomplished by developing with ferrous sulfate.  I think the 
Rockland kit provides thiocyanate (or maybe tries to get by with 
thiosulfate) as a developer additive to keep grain size small and 
promote whitish silver deposits.

Thiocyanate is also used as a component of "real" reversal 
developers, to clean up the highlights; and of holographic 
developers, to keep the grain small.  Sodium sulfate is generally 
used with gelatin emulsions to prevent excessive swelling of the emulsion.

Best regards,

etienne