Film darkening quickly - AFTER - developer bath ?

Silverhalide Emulsions / Chemistry.
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thycore
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Film darkening quickly - AFTER - developer bath ?

Post by thycore »

Hia !

Many thanks to all folks who helped in finding appropriate chemistry for my new —20 years old old— "Holofilm 250" box.

Now I have a probably basic question :

I expose a film for 10 seconds under my laser, then I drop the film in the developer bath (Kodak D-19) for 3 minutes until I can clearly see the dark gratings on the exposed areas.

Under my green safelight I see a perfecly transparent film with nice dark fringes in the middle.

At this point, I have not "yet" dropped the film in any cleaning bath, nor bleach.

I turn on the white light of the room, and the film darkens very quickly (and more or less entirely excepted the laser-exposed area which seems lighter in the end).

Usually when processing some other plates I had until now (Ultimate, Integraf..) I was not able to observe such phenomena.

Is this my developer bath getting old ? (I developed something like 10 films in it since 4 days) or is it due to some unfinished reaction which could have been stopped if rincing in de-ionized water ?

In case of my chemistry is getting old or saturated somehow in halides or whatever, is there a way to regenerate it partially (instead of throwing it all and cooking some fresh one?)
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thycore
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Re: Film darkening quickly - AFTER - developer bath ?

Post by thycore »

I found out thanks to google xD (stupid me xD), of COURSE film would darken after the developer bath if not rinced.

In case any holo beginner would ask the same question someday, i'll put a couple lines of the explanation :

The developer bath only reacts with exposed silver-halides in the film.
Therefore, after it has developed the exposed silver-halides, the remaining white/transparent parts are still light-sensitive, meaning that if you do not rince the developer chemical which are on it it will continue processing the film whenever some light comes and expose the silver-halides.

So, yes, rincing after developer bath is absolutely necessary (I even read about "stop bath" where an acid bath is used to competely disable the developer agent, which requires alcaline environnement to work).

The bleaching (also referred as Fixing) step is also mandatory to clean the film/plate out of any remaining light-sensitive material !
lobaz
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Re: Film darkening quickly - AFTER - developer bath ?

Post by lobaz »

You are right, you cannot turn the light on after development.
A few slight corrections:

developer - attacks silver halide in the emulsion and makes the exposed part dark

rinse - water washes the developer away, which means that the process of darkening stops

stop bath - can be used is you need to stop the darkening process immediately
(after plain rinsing the development can continue if the developer was not completely removed)

fixing - after rinse or stop bath, the emulsion still contains light sensitive material. Fixing bath removes it from the emulsion.
(this step is often omitted in holography for various reasons)

bleaching - the dark parts of the emulsion are converted back to fully transparent ones. Bleached holograms are also referred as 'phase holograms', while the unbleached ones as 'amplitude holograms'. Phase holograms are much brighter, amplitude holograms can be less noisy (but are much, much darker).

For more details, read e.g. Chapter 5 of Practical Holography by Saxby (and Zacharovas).
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thycore
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Re: Film darkening quickly - AFTER - developer bath ?

Post by thycore »

Thank you for this very clear answer :-)

Would be a great idea to put this question in the wiki for other holo-begginers !
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