One of George Eastman's earliest (?) patents was for coating glass plates by running them, upside down, across a roller half-submerged in emulsion. After passing the roller the plates were flipped right-side up to dry. See here. The roller continually lifts emulsion up as it rotates and transfers emulsion to the plate; thickness being determined by (amongst other things) viscosity.

This seemingly simple technique is all but forgotten, no? I'd be curious to hear anyone's thoughts about it.

If you go antiquing frequently, you've undoubtedly come across those old porcelain envelope moisteners (see picture). These embody the same basic idea and indeed, I'm wondering if they wouldn't work for coating rolls of film, if modified somewhat.

Just throwing this out there..