Quote Originally Posted by robopro View Post
This may have already been discussed, but, when making an emulsion is there a good way to acurately determine the ISO (or ASA) of the emulsion?
The emulsion has to be coated and made into the form of use first. Then follow the ISO method for the particular kind of the emulsion. Different kinds of emulsion use different measurement to determine the speed.

Is it possible to 'set' the speed to a predetermined factor -- meaning can one make an ISO 100 B&W emulsion with any fair degree of acuracy?
If not, why?
For most of the time, no. There are many factors that affect speed and you don't know the speed until you make a test batch with exactly the same material, method and technique.

Experienced emulsion makers have accumulation of data from an emulsion made with one or two variables shifted within a reasonable range. In this case, it is possible to aim a specific speed a priori. Even so, you typically make a test batch to confirm that the emulsion is exactly what you need.

In reality, pictorial photographic emulsions are a blend or multilayer coating of 3-5 individually prepared emulsions. (In case of color, for each color layer, there are at least 3 emulsions involved.) The speed of the material is again influenced by the blending of the individual emulsions as well, although it is largely determined by the fastest one.