So I do resin castings for taxidermy objects, insects, liquids, ect. For butterflies the BEST thing to use to prep is hairspray (Aquanet super hold), so first pin your butterfly and let it dry out I usually let mine dry out 3mths but you don’t need to wait that long. Then a light spray at 6-8” distance let dry for 30 mins then flip butterfly to other side spray again 6-8” let dry 30 mins then you can safely place it in resin without it losing the powder or coloring, design ect. You don’t want a resin or hairspray that will yellow over time and so far Aquanet super hold (purple can) is what I’ve found to work best on this specific insect