--- In
Homebrew_PCBs@yahoogroups.com, "Peter Leybourne" <peter.ley08@...> wrote:
>
> I'm not familiar with Kodak PRD film, however, this is from my photography days.
> Kodachrome colour slide film has a very distinct colour cast as it ages. The processed slides turn pink! Your film will probably be old stock, albeit unprocessed which could have something to do with it.
>
> Exposing photographic slide film in a camera to capture an image is usually for only a fraction of a second - 1000th of a second sometimes. It follows, any handling of film must be done in total darkness otherwise it will fog.
>
> The same applies to printing paper although it's not so light sensitive. Small amounts of stray light on the paper before fixing will turn it pink. If that happens, the pink colour cast is 'fixed' and will not clear.
>
This is a special litho film with a sensitizing dye to make it red sensitive. It is designed specifically for use in a laser photoplotter. I have been using similar films, first from Kodak 15 years ago, and then two different Agfa films. This new experimentation is because I am down to the last 5 sheets of the Agfa film, and they are out of the business. I have the recommended safelight (a dark greenish-blue tube over a 48" fluorescent tube), they spec the same one as agfa did. This film is a good bit more sensitive than the Agfa film, but can still be handled for minutes under this safelight without fogging. Yes, this is pretty old film, but the Agfa film I have been using is over 12 years old, and still working fine. The PRD is about 9 years old, so age could be a factor.
Are you saying that exposing the plastic film backing to light sensitizes it, and the fixer "develops" that exposure into the pink color? Gee, I hope not. It is true that this film is mostly intended for automated processing, so most users could probably avoid this trouble. They also usually use a machine developer with hot developer and fixer.
My exposure is 5 microseconds (per pixel).
Jon