I was recently asked whether homemade silver gelatin emulsion is as "good" as, say, Tri-X, and could it conceivably replace it. I realized that I couldn't answer this question as asked, and the reason is revealing of a fundamental difference in what homemade emulsion is as opposed to the commercial product. For me, at least, the goals are completely different.
Kodak, to use them as typifying the photographic industry, started with the goal of achieving what they understood as good -- or even perfect -- photographic representation. They then took a physical and chemical process that seemed like it could support their vision, and proceeded to work with it and incrementally modify it so as to make it give them the results they wanted. They spent years and a fortune doing this, and they got pretty close: modern film is pretty close to being invisible in itself: you can shoot something on film, and trust that when you get it back from the lab (or develop it yourself) it will present a picture of exactly what you shot, without calling attention to itself. It's just a window, inobtrusive and transparent. They worked very hard to achieve this, and modern commercial film is a remarkable testament to mind imposing itself onto matter.
This accomplishment is particularly noteworthy because, in fact, silver gelatin photochemistry is a rather quirky and difficult physical phenomenon. It's easy to see that it works, but it took a lot of research and development and tinkering to get from the first Daguerrotype with its very long exposure times and irreproducibility and high cost to the low-light spontaneous snapshot or the idea that you can buy thousands of feet for a shoot and trust that it will all behave exactly the same way and that will portray detail, light, shadow, even color, "accurately" so that the viewer forgets about the fact that they're watching a film, and they lose themselves in a simulacrum of another reality fundamentally like their own. The idea -- perfect representation -- came first, and the physical world was forced to enact it, like a circus performer forced to do a stunt.
What one does in making emulsion is fundamentally different. You are starting with a physical phenomenon that exists in the world -- the light sensitivity of silver halides -- and asking "what can it do?" It changes color when exposed to light. That's a pretty neat property. What artistic possibilities does it offer? I'm not approaching it with overbearing ideas of what I think it HAS to do. I'm not putting together a shoot that costs many thousands of dollars a hour and involves a hundred people and a rarely available location such that the film had better just do what's expected of it and not fail because I can't afford to repeat it. In that case, the film is a servant, a teleological necessity of no importance in itself. It is in this paradigm that the film versus digital argument proceeds, and it is in this paradigm that film will lose the argument. If your starting point grants that the medium should call no attention to itself, assert nothing of its own nature, then what could you possibly have to say if someone comes along with another medium that achieves the same goals and offers numerous other advantages besides?
This reflects a fundamentally different attitude towards the world, one that was well articulated in the 1960s and widely perceived: the difference between approaching nature as a blank slate onto which we inscribe our vision, a resource without character to be molded and shaped into exactly what we want: nature as slave. On the other hand, a living thing with which we enter into dialog, striving to understand its nature and collaborating with it to achieve goals which reflect equally the nature of the world and the nature of our vision: nature as partner.
So, to return to the question. To answer with some number -- "the resolution is 30% the resolution of Tri-X" -- is a bit like saying "an apple has 30% of the flavor of an orange." It may be possible to pick some scale on which it is possible to compare the two, like vitamin c content, and any one orange might have more or less than any one apple, but limiting the terms of the debate narrowly enough to make a meaningful comparison by nature forces the debate into terms appropriate to the commercial and not the handmade. Any particular batch of handmade emulsion may be comparable to a commercial film stock, but the comparison is misleading, because whereas the commercial film is the fruit of many years of expensive R+D that worked to achieve an optimum and consistent "resolution," handmade emulsion is a quirky inconsistent thing whose chief virtue has nothing to do with optimums of any kind. If it goes head to head with the commercial product, it will lose. More importantly, I would say that's not the point. It's the wrong question. If you want commercial results, buy commercial film. If you want to make your own, cast aside instrumental goals by which what it actually is could be judged as falling short of what you want it to be, and embrace what it is as a given to be explored.
To make your own emulsion is to embark on a journey into a different world of image making, one in which standard thinking must give way to physical realities that don't match convention. It's not going to be "as good," and that's beside the point. Ask, rather, what is it good for? What are its inherent properties, and how can they be worked with? We're not going to repeat Kodak's years of hard work in our basement, so why try? Let's do something else, something that they didn't do because it didn't match their objectives, neither aesthetically nor commercially. We don't have to sell it or be driven by a need to make money from it. That opens up enormous possibilities that Kodak could never pursue, burdened as it was by commercial necessity and the aesthetic conventionality this required.