Hey everybody!

Here's an example of Mark Osterman's ability to draw, and illustrate ideas in really simple, elegant ways. This is a flow chart showing the most basic steps of emulsion making; in this case a washed emulsion.

The other day Ron joined us at GEH and he too made his way to the chalkboard and we had an excellent classroom session. We hope to do this once a week, or at least a few times a month, in addition to lab work, coating, processing, etc.

There is one term in this drawing that is perhaps not entirely technically correct; or rather, is not in line with the nomenclature that I've learned from Ron's book; Digestion.

Digestion implies the presence of silver-halide solvents (ammonia) and/or chemical sensitizers (sulfur, gold). [Ron, please correct me if I'm wrong here...]

In the simplest form of an emulsion, the prolonged heating step after precipitation of silver-halide is called ripening. This is the process of redistributing and resolubilizing the AgX grains, which on the average, results in larger grains and in turn, more speed.

If you imagine the state of grains after precipitation, we have a distribution of different sizes; some large and some small. The smaller the grain, the more surface area it has by weight. Thus, these smaller grains will become soluble in the presence of heat to a greater extent than the larger grains, and they will redeposit (on average) on the larger grains. The result is 2 fold; more speed from the formation of larger grains and more contrast, as the distribution of grain sizes becomes narrower (less latitude in effect). The pitfalls of course are fog and the destruction of the gelatin's setting point if too much heat is applied.

"Nearly all the mechanisms in silver-halide emulsion making are surface phenomenon"; Ron's million dollar quote.