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The use of a brayer is a good idea, when you might think of using is a hand roller on a flat surface like a thick plate of glass to uniformly spread the photosensitive paint. The glass and roller can both be easily cleaned. Another idea is using a photosensitive spray.
I have seen etching time reduced by reducing the hydrogen peroxide in order to reach 30% strength. I enjoyed your results/methods which so far are the top methods but have never seen the salt being added.