Umm, Denise, it is time for me to expand on my comment above.

In a single run emulsion (Silver Nitrate into salt and gelatin), it is the size vs freqency distribution and grain type and size that matter. In this single run (SR), the concentration of salt decreases with time and thus a different size and different grain type form. The size and shape is all over the map with a slow addition, and this gives low contrast and (mainly) higher speed due to the larger crystals that can form during the long pptn.

With a fast addition, the grains are mostly the same size and shape because they all form pretty much at the same time and thus see the same salt (and gelatin) concentration. They are smaller and slower.

With any emulsion, all else being the same, lower gelatin gives larger grains and higher speed. More gelatin gives lower speed and finer grains. Keeping things contrast and doing a time of addition series, the speed goes up and contrast goes down. In the early days, this was the major means to control contrast. In fact, early high contrast emulsions were made by dumping the Silver Nitrate over the side in one big "splash". A side note: if gelatin at the start goes much below about 1 or 1.5%, you begin to form "crunchies" which are often the size, shape and feel of corn flakes. In fact, you can use a coffee filter to determine if your gelatin level is reasonably good. If you have a lot of residue in the filter, it is likely that gelatin is too low for the conditions. Adjusting conditions can be a long and difficult task for one not trained in the art.

See example below of pptn time vs contrast and speed!

Now, if a double run or an Ammonia salt is used, this is all quite different.

I hope this gives you a clear understanding. I would be happy to give a complete workshop on this and more, free to you Denise, should you ever make it to Rochester. But, I hope this further increases your understanding of emulsion making.

BTW, this figure is in my book along with a page or so of explanation.

PE