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For me, sanding the balsa roughly will ensure even powder retention and is less messy, in the long run.
Oil will often stay and makes for a pasty mess to remove from your blade.
Dry and dry...

Man, I just block sand a piece of 3/16 balsa with 100 grit wet/dry, sprinkle a tiny bit of the powder up and down and start rubbing it around with the green finger. It spreads nicely all around.
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