There is a video to watch on line that shows a 20 x 24 inch plate being poured. It is on the John Coffer web site.
On the left side it says "videos", go there and choose the longest one, ten minuets.
Now, this is a wet plate video, but it is a huge plate that is hand poured. I am into dry plates and have hand poured 4 x 5 inch plates and am sweating how to do 12 x 15 inch ones. I suppose that if the liquid emulsion is thin, warm, and spritzed with Everclear it'd cover a large surface in red light. Perhaps a piece of marble could be warmed and the glass set on it. If there was a gimble under it, it could be tipped this way and that and thus eliminate hot finger spots. John used his hands, but he used a metal plate. It didn't matter.
Has anyone here poured large plates for dry plate photography? How?