Well, while I'm on a roll, here is another.

Coating technology first started with what amounts to an offset roller that picked up emulsion from a tank or well, and rolled it onto the film or paper. It could only coat at about 10 ft / min and was subject to lots of defects.

Drying was achieved by means of draping the film or paper on wooden slats suspended from the ceiling and these slats introduced defects in the coating that were spaced at 2x the ceiling height. Therefore, a 50 ft ceiling allowed about a 100 ft max coating length with minimum defects due to the buckle or curvature introduced by the wood slats that held the paper or film.

The next method involved addition of a blade that scraped off the excess emulsion making for better uniformity. The blade was either a metal knife or an air knife.

These methods were limited to coating speeds of 10 - 100 ft / min, preferrably the lower limit.

These methods are no longer used except by one or two isolated plants that are of the older design.