Emulsion making in concept is fairly easy. In practice, however, it is an incredibly complex undertaking.

First off, you have the gelatin. It has to meet certain standards of purity -- meaning it can't have the wrong impurities, but it needs to have some of the right impurities. (Shortly after Eastman started manufacturing dry plates, he had a large batch fail. Investigation traced it back to the sulfur content of that batch of gelatin. This product failure played a large part in the formation of the Kodak Labs.)

Once you have the gelatin, you have to very carefully and consistently add the other ingredients (i.e., the silver, the halide(s), the sensitizers, etc). Then you have to let the emulsion age for a period of time.

Once it has aged, it has to be allowed to solidify. It is then shredded and carefully and thoroughly washed to remove all of the excess and byproduct chemicals.

Then you get into coating...

While much of the basic science of emulsion making is quite well documented in the literature, there is a great deal of proprietary, unpublished knowledge involved as well. Kenneth Mees addressed this in the preface to his book "The Theory of Photography" saying that he had to basically ignore that whole aspect of the science because much of his knowledge of it was acquired via his work for Eastman and was therefore nondisclosable.

I have a great fear that, because so much of this is proprietary, it will be "lost" information should the major manufacturers cease manufacturing film.