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View Full Version : What Emulsion Parameters Affect Developability?



analogsnob
05-07-2011, 09:48 PM
Developing times have been drifting shorter for some time, favorite techniques such as water bath and divided development do not work as they once did. "Conventional wisdom" if such a thing exists would hold that emulsion "thickness" has much to do with it. I have learned in my readings and here that it is most likely more complex than that but what does effect which developing agents work best and why would the old techniques no longer work or how would one design an emulsion that would respond to them?

Ray Rogers
05-08-2011, 07:57 AM
I think it is a good question.
I can give you a simple answer, but it is necessarialy incomplete.

First and fomost is the developability of the silver halide itself...
Silver halides are a group of different chemicals which differ in their properties, developability for example.
These can mix more or less freely and even form "solid solutions". So a "light sensitive emulsion" can varry a lot in composition. AgCl develops quicker than AgBr and AgI, IIRC, is more difficult to develop than either.

How or where these are present in the emulsion crystals will dictate how quickly the developer develops.

I suspect that while an easily developed silver halide may develop well in a mildly reducing developer,
a stronger reducing agent may be more suited (or even necessary) for one that develops with difficulty.

I am not sure how important all this is with "normal" materials, but to answer your question,
One would choose to incorporate a larger amount of the specfic silver halide which responds as desired to the reducing agent you have in mind, and/or that same silver halide in an appropriate crystal structure that allows it's properties to be expressed as desired.

Incomplete but a start anyway.

Ian Grant
05-08-2011, 08:06 AM
You can add emulsion thickness, type of hardening, use of developer adjuncts, surfactants etc.

Ian

analogsnob
05-08-2011, 08:52 PM
Again to speak in general terms about something where specifics are important, to obtain an emulsion that functions better with techniques of development relying upon exhaustion effects of developer carry over one may simply coat it thicker? Would a higher percentage of gelatin be required?

What has changed over the last 30 years? Is it as conventional wisdom states that the emulsions are just thinner?

Photo Engineer
05-08-2011, 09:18 PM
Emulsions may not necessarily be thinner. An AgBrI may have core I, distributed I or surface I. Each of these will develop differently all other things being equal such as thickness and grain size. Addenda, gelatin type and other factors influence development rate as well. This is why a divided developer is so chancy. It must be fine tuned for the emulsion thickness, gelatin type and emulsion type. It is not necessarily a good idea to rely on divided developers, stand development or other techniques such as this across films. Each of these must be fine tuned for each film and process condition before it will work best.

PE