Applicators like this for the paint industry have been described here and elsewhere. They are made of untreated aluminum for the most part, and run about $1200 for a 4" blade.
Oh, I won't ever be making a blade. I was just speculating, for general conversation and further knowledge. Sometimes ideas and thoughts put down into sentences and paragraphs can cause new directions in thinking. I was just trying to stimulate discussion about all the options possible.