[alt-photo] Re: tintype
zphoto at montana.net
Wed Nov 3 14:38:57 GMT 2010
You are right, the Rockland kit is not "real" tintype but liquid emulsion.
I should have also clarified that the thiocyanate or the thiosufite as it may be is mixed IN the developer along with the other two. In other words, none of the three solutions are used to fix, they are all mixed together and used to develop. Fixer is separate.
I know from chromo that the thiocyanate is the chemical responsible for essentially fogging the paper in the absence of room light (according to Jolly) so my guess is the mixture of the three chemicals is responsible for fogging and producing that characteristic milky/brown tone on the modern tintype.
However, I still cannot find if it is a 50% am thio or 5% sod thiosulfite. That is what I am interested in.
Some make-do tintype developers just tell you to mix exhausted paper fixer into the dektol as well.
I have a call into Rockloid and also an email but no response yet.
Christina Z. Anderson
On Nov 2, 2010, at 7:42 PM, etienne garbaux wrote:
> 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,
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