[alt-photo] Re: direct positive paper

[etienne garbaux]

Richard wrote:

>I don't remember the full theory of the direct positive material I 
>am thinking of but its designed to take advantage of the reversal of 
>the image under high exposure. Most modern emulsions do not have 
>such a reversal region because its not desirable in normal negative 
>and positive materials. The effect can be exagerated to the point 
>were an exposure of reasonable amount will cause the reversal. The 
>material will be dark if developed without exposure.

Kodak professional direct duplicating film types 4168, SO-339, and 
SO-132 were the paradigmatic examples of this type of film.  Kodak 
used to publish a very detailed booklet describing the technology and 
use of these films.  They have been discontinued for more than a 
decade.  Essentially, film with a very substantial reversal region 
was flashed at the factory to the reversal point.

Best regards,

etienne