There is a video with the URL somewhere here, showing a curtain coater in operation via an animation. I wish I had saved that URL. In any event, it is a very good illustration of the subject.
And, I don't disagree with anything anyone has said. I would like to point out that modern coating is more akin to making a microprocessor than a vacuum tube, and what we are doing in our home labs is more like making a crystal set, not anything like as complex as a vacuum tube or radio using one let alone something that uses the hypothetical hand-made microprocessor.
So, thus far, most of you have only seen the simplest extreme in making and coating, IE the equivalent of making a crystal set. And, if you want to take a step up, you have to bear the cost of the education, the cost of R&D and the cost of the equipment needed to make and coat at this higher level.
It is so easy to be dismissive of what I say, but I am pointing out a fundamental truth and that is that future coatings with any quality and quantity will come from existing facilities. Next will be expensive hand made products that fill a niche but are produced in moderate quantity and a medium to high price and finally are the home made hand-crafted materials which I have been fortunate to have taught some to make.