One of the reasons collodion has attracted modern practitioners is its original history. Due to the nature of the beast, wet plates could never be commercially produced - at least not the final product. Because photographers poured their own plates in the field for over twenty years, we know it can be done.
Gelatin dry plate, on the other hand, was the Holy Grail delivered to the 1880's photographic industry. Cameras and printing papers were already being commercially produced, now so could the negatives. The sales loop closed. Kodak especially sold a message along with its products - "modern photographic materials production is so complex only the experts can do it". It was marketing, pure and simple, but the message took root fast and deep. You can still hear it from Kodak and ex-Kodak people today. And, unfortunately, too many people still believe it.
By 1940, the photographic industry was infamous for its secrets. And, without a doubt, by that time they were making products that we'd have a hard-to-impossible time reproducing in our darkrooms. But, anyone can make the early emulsions. It is both safer and far easier than collodion (Although I have to admit, hauling your darkroom around in a covered wagon is pretty cool. Never want to do it, but I can see the attraction.)
Coating was one the first things to go mechanical. Because it's hard to get clean edges on plates, huge pieces of glass were coated. After the emulsion set up, the unevenly coated salvages were cut off and the big sheet was cut into smaller plates. It is possible to pour-coat with practice, but the emulsion will rarely be completely uniform. That's perfectly ok, if that's a look you want. I prefer my plates as nice as I can get them, so I borrow from the idea of the old coating machines, but rather than cut off the selvages after coating, I essentially do that before coating. Since a picture is worth a thousand words, here's a picture or two:
http://thelightfarm.com/Map/DryPlate/PlatePrep/DryPlatePart4a.htm
Denise
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