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Ferrox is Ferris Oxide / Iron Oxide (pure powdered rust)
usually a lot finer & softer than Chromium Oxide (Chrox)

yeh mate rub off any excess paste with a clean cloth then let it dry some more
it is surprising how much a small amount will spread

now I currently have an experiment with some polyester felt...

I have used Chrox & Ferox on 2 Balsa paddles 3"x8" about
I fully painted solid cover of each powder mixed with fine mineral oil
it doesn't take much only a few drops & it will cover the area quick...