A simple technique, but not forgotten. A quick search will turn up any number of links to companies producing small coating machines. Most are aimed at specialist labs needing repeatable coatings on an assortment of substrates. The same idea is also used in the electronics industry for soldering components to circuit boards.
Originally Posted by holmburgers
I have trouble getting consistant defect free coatings when I make glass plates, and have considered a roller. Cleaning and wastage put that idea to bed, but I've also considered spin coating as a potential answer.