>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.>
None of it particularly good news Jon.
I'm out of touch with PRD techniques.
Personally, I would treat all film as light sensitive. Always keep it under wraps and only work in 'safe' or subdued light. 'Safe' is not all it seems. I saw a film developed that had been lying dormant in a 'Box Brownie' camera for very many years. You may have seen the little red window on these old cameras which show the frame number on the backing paper. Light had gone through the red filter, through the backing paper and exposed the film to a red circle with a number in the middle. How safe is plastic film backing over long periods?
In the case of colour slide printing paper, the answer to your question is yes!
Stray light prior to developing/fixing may cause the pinkness you describe. The same applies to slide film although because of film speed vs paper speed, complete fogging usually occurs.
Artificial light and sunlight have different colour temperatures. Colour slide film is designed for daylight exposure and slides will have a red/pink colour cast if the film is used under artificial lighting conditions. What we see as a white light table lamp will be very red in the picture. A flashgun or blue filter over the camera lens will correct this.
The picture printing process is a positive print from a positive slide on light sensitive paper.
If stray light spills onto the paper prior to development, it will cause a pink colour cast to the finished print. In extreme cases where complete fogging occurs, development will turn the paper red.
As mentioned, I have Kodachrome colour slides from military activities in Yemen taken in 1964. After nearly 50-years, they are all quite pink. Kodak film products IMHO were never as stable as one would wish. They were first class when fresh, but over long periods the quality of dyes deteriorated. Ektachrome had a tendency to turn blue. Agfa products on the other hand seemed more stable. I have 40-year old Agfa movie film which is unchanged.
So, this could be the root of the problem. If the film has not already exposed to stray light, the answer might be to try working in very subdued light. If the film has been inadvertently exposed or the emulsion has deteriorated, there's not much anyone can do
Peter
MM5PSL
----- Original Message -----
From: jmelson2
To: Homebrew_PCBs@yahoogroups.com
Sent: Monday, March 07, 2011 5:39 AM
Subject: [Homebrew_PCBs] Re: Kodak PRD film ?
--- 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
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