The book "Silver Gelatin" describes a variety of methods of making coatings in the darkroom. Among them are included brush coating (paintbrush and foam brush), dip coating (using a tray of emulsion) and spraying emulsion on the support. Very good examples are shown of all of these. I suggest that those interested get a copy of this book.
I have found that brush coating almost always leaves brush marks, and foam brushes often cause bubbles to form in the coating. I have gotten very good coatings from both methods though.
Dip coating is quite good and was used in the early days of manufacturing of photo products.
Paper is placed, face down in a tray of heated emulsion, and then is lifted out while dragging the face (emulsion) side of the paper over the edge of the tray to scrape off excess emulsion. It can also be lifted out of the tray and allowed to drip off excess emulsion. I have seen this done with good results, but I find that it varies quite a bit and you cannot adjust the amount of emulsion coated on the paper. It is not very good with film.
Plates are traditionally coated by pouring the emulsion onto a warm plate and then rocking the plate from corner to corner to get an even coating. Excess is poured off back into the container of warm emulsion. I have done this, but have not mastered the technique. Among other things, the plate coating method requires a precise salt, gelatin and surfactant balance to adhere well to the plate during processing. Early plate formulas used ethyl alcohol at high concetrations to assist in spreading the emulsion evenly. Everclear is the only suitable product on todays market, and it is not available in most states.
In Kodak Research, it was necessary to make small hand coatings routinely. So, a method was developed for film, and another was developed for paper. Basically, it involves the use of a doctor blade modified for the desired support and the blade is moved over the support, rather than having the support move past the blade. There were about 3 designs of doctor blade in use for film (and also for RC paper) and one design in use for baryta or regular paper as well as RC paper.
In this method, typically, a blade was adjusted to a given undercut or gap and the emulsion was poured onto the support ahead of the blade. Then the blade was moved over the puddle of emulsion and the blade scraped off the excess emulsion and spread it over the remainder of the support.
Using this method, a 0.005" (5 mil) undercut, will use about 12 ml to coat 1 square foot of emulsion and from this, the amount of silver can be calculated as well as the amount of gelatin. The spread is very even up to 8x10. I am currently working with a prototype 11x14 blade and a prototype 16x20 blade is in production.
Film and RC blades are very similar, but plain paper blades differ substantially. A plain paper blade can be used with RC, but can cause severe defects with film. A plate coating blade has been made at EK and I have made one to that general design myself.
I think that very high quality coatings up to 16x20 are possible, but to get that quality the actual coating must be larger than the desired print for the same reason that machine made coatings are larger than the desired final stock. There are startup and ending defects as well as edge defects in every case, so the coating must be longer and wider than the finished material that you desire. For example, and 8x10 is actually 8.25" x 12" to allow for these defects.
I think that some form of emulsion making and coating is the future of B&W high end art photography, particularly in prints. I have used a variety of paper surfaces, and am surprised at the quality that I get from Watercolor and Velour papers. Just like old times to me!
I might add that very complex coating blocks with vacuum hold down and heating and cooling were used at EK. I have found ways around this, as the block would be very expensive for the average photographer. Work is progressing and has been posted by one of my students as she comes up to speed. You can see this in my post regarding the update to my workshop if you are interested.
Hand coating is a real, possible future for the photographic enthusiast interested in silver halide emulsions. In addition, I have coated Cyanotypes and other alternative photo systems using this. The only ones that didn't work are Pt/Pd systems due to oxalates interaction with gelatin. I intend to work this out as well, if at all possible.