I always thought that the process of ND filter making is a pretty mechanical thing. That you would place a sheet of glass on one end of the machine, press a button and then a constant stream of ND filters would fall onto a conveyer belt.
It turns out it is not so, that the process of filter making, at least at Lee filters is almost entirely manual.
In the movie blow, Mike Browne take the grand tour at Lee Filter’s factory going through the different stations from making the resin, through various inspections, coating it with dye and shipping it off. I was really surprised to see how much manual labor goes into the process.