[alt-photo] Re: tintype

[Richard Knoppow]

----- Original Message ----- 
From: "etienne garbaux" <photographeur at nerdshack.com>
To: "The alternative photographic processes mailing list" 
<alt-photo-process-list at lists.altphotolist.org>
Sent: Tuesday, November 02, 2010 6:42 PM
Subject: [alt-photo] Re: tintype


> 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
>
    Are you sure potassium cyanide is necessary for fixing 
wet plate? My understanding is that ammonium thiosulfate 
(rapid fixer) has sufficient power to fix out the silver 
iodide. Thiocyanate would be even more powerful but still 
safe compared to the cyanide.
    However, I am just asking that, I agree with your 
analysis of the Rockland process. Tintype is not a reversal 
process although its a direct positive process. It relies on 
the reflectivity of the silver image rather than its 
density.

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