[alt-photo] Re: tintypes

[Richard Knoppow]

----- Original Message ----- 
From: "Mary Donato" <gneissgirl at icehouse.net>
To: <alt-photo-process-list at lists.altphotolist.org>
Sent: Thursday, November 04, 2010 7:56 AM
Subject: [alt-photo] Re: tintypes


> Chris,
>
> Please let us know about your results when you have a 
> chance to make and test your reversal developer recipe.
> I had a lot of fun a couple of years ago making dry-plate 
> tintypes with the Rockland kit (in-camera, tiny, square 
> format things, so cute).
> Then I ran out of developer :( and everything came to a 
> screeching halt.
> I didn't want to order a gallon, and it's pretty 
> expensive, anyway. As I recall, the shelf life of the 
> developer is fairly short. I didn't have any joy with the 
> exhausted fixer thing. So I'd love to be able to make 
> small batches of developer. Bet I'm not the only one, too!
> Thanks for sharing the info!
>
> Cheers,
> Mary
>
> http://alternative-ego.com
>

      I think the Rockland tintype process is not a reversal 
process. However, the silver solvent in the developer may be 
there for the same purpose as in a reversal first developer, 
namely to eliminate veiling due to very fine silver 
particles that are not removed in fixing.
     Tintypes rely on the reflectivity of the silver image 
itself. A similar effect can be seen in very thin negatives 
made using extra-fine-grain developers like Microdol-X or 
Perceptol, that is that there is a weak positive image by 
reflected light.
     If you are interested in actual reversal processes 
there is some guidance in the old formulas for reversal 
development of motion picture film, very commonly done for 
home movies. Because most reversal was done for the purpose 
of direct viewing or projection the processes were designed 
to produce a gamma of around 1.0 or even a bit higher, and 
the highest density the film of which the film was capable. 
It _is_ possible to modify the process for lower contrast. 
One would want that for instance for making duplicate 
negatives directly from a negative.
     The nature of the process is such that the first 
developer should be formulated for the particular film its 
going to be used on. The first developer is usually a high 
contrast type and usually contains a silver solvent such as 
a thiocyanate or thiosulfate. The purpose of this is to 
prevent veiling of the highlights by residual silver halide 
particles which are so insensitive to light that they are 
not exposed during the image exposure. If left in the 
emulsion they will become developable in the second 
developer due to the fogging step and will cause a veil in 
the highlights. The use of the solvent substantially 
increases the speed of the film when used for reversal. The 
amount needed depends on the emulsion and must be determined 
by experiment.
     I have a number of old formulas for reversal processing 
and will post them if anyone is interested. However, the 
first developers are similar to Kodak D-19 or even Dektol 
with the solvent added, and the second developer is the same 
thing without the solvent, or sodium sulfide if one wants a 
sepia image. If a sulfide second developer is used no 
fogging step is necessary. Bleach is a conventional 
dichromate type.
     Reversal can also be used for printing paper. I believe 
the old coin photo machines used a reversal paper.
     Virtually any negative emulsion can be reversal 
processed but I think the old motion picture films for home 
movies had emulsions designed to yield the necessary density 
and contrast for projection.
     A problem with many 35mm negative films is that they 
contain a pigment in the support for the purpose of reducing 
the conduction of light laterally through the support (light 
piping). This pigment is not removed during processing, and 
indeed, can not be removed. It adds some density to the 
resultant positive essentially cutting down screen 
brightness when projected.



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