[photo-3d] Re: Copying Glass Negs

[CanterMike@xxxxxxx]

--- In photo-3d@xxxx, Peter Homer <P.J.Homer@xxxx> wrote, in part:

>Perhaps black and white transparency film could be used and the
first 
>negative stage of development omitted going straight on to the
second 
>dye developer to produce a dye based negative image.

Sorry, Peter, but the current range of standard B&W 
slide films don't use dyes.  Only colour slide films 
use dyes.  B&W still uses good old fashioned silver 
halides.  In the B&W reversal (slide) process, the first 
developer step is very much like a basic negative developer 
(in fact, is often exactly that...if you were to fix the 
film right after the first deveopler you'd have a negative).  
The slide process diverges after the first developer, when 
the developed silver crystals are bleached off, leaving the 
undeveloped crystals in place.  These are then re-exposed 
(either physically to a light source, or by a chemical), then 
developed by the second developer.  Only the is the film fixed 
(to remove any crystals left unaffected by either developer) 
and washed.

B&W films do exist that use dyes as the final image (Ilford's 
XP2, or Kodak's T400CN & Portra B&W), but currently only as 
negative films.  These are processed in colour chemicals (Kodak 
C41 or equivalent), where ALL silver is bleached out of the 
emulsion, leaving only the dye layer(s) behind.  It is certainly 
possible to develop them in slide chemistry (Kodak E6 or 
equivalent)(this is known as "cross processing") but it is not 
what the film manufactures have designed them to do, and so your 
results may vary dramaticly.

Mike


 

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