From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 11/20/00-09:38:37 AM Z
At 07:22 AM 11/20/2000 -0800, you wrote:
>
>
>> The other approach mentioned by Judy: Making enlarged negs (lithographic
>> film) from original negatives by direct positive method is not approprite
>> for me because I want my large negs to be developed by a staining
>(negative)
>> developer.
>
>
> I have had very nice results from Astia (6x9) positive enlarged directly
>to lith file (the 'cheap'
>Freestyle stuff) for ZIA and kallitype. WOnder if anyone has used SCALA B/W
>slide film from
>Ilford for alt???
>
> Terry ROth
>
Scala is an Agfa film. Agfa does not publish processing instructions for
it, it must be sent to one of the labs set up for it.
As far as I can find out Scala is a conventional reversal film, similar
to the B&W reversal films sold for making home movies for years. It can be
successully processed in the reversal kit made by Kodak for T-Max and
Technical Pan films or the kit Tetenal sells. Evidently the Tetenal kit is
not available in the US.
Someone posted reversal formulas. The reversal process is not
complicated. The first developer is the critical step. Correct exposure
index and development time will have to be determined by experiment for
films not sold for reversal. The first developer nearly always has a halide
solvent in it to improve film speed and clarity of highlights in the
finished reversed film. The solvents traditionally used are thiocyanate or
thiosulfate. The developers tend to be fairly high contast types, a typical
one being similar to Kodak D-19 wth the addition of the solvent.
The bleach is a conventional chromic acid bleach followed by a sulfite
clearing bath to bleach out the yellow stain. The bleach must be a type
which removes the silver without converting it back to a halide.
The second developer must be a low solvent developer. It will have little
effect on grain because the silver left after bleaching is nearly all the
slowest, and finest grain, particles of the original emulsion. A developer
like Dektol or D-19 works fine. High sulfite developers, like D-76 will
tend to dissolve some of the very fine halide grains of the reversal image
before they have a chance to develop.
Reversal processes are always touchy compared to negative - postitive
processes since there must be a reasonable amount of halide left after
bleaching and there is little variation possible of the contrast of the
final image once the original negative image is developed.
---- Richard Knoppow Los Angeles,Ca. dickburk@ix.netcom.com
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