Probably a photo of the problem would help, as there are nicks and then there are NICKS .............once folks see what the problem looks like, they will be flooding you with solutions or suggestions - IMHO

Here is picture of lotus leaf. with a nick I haven't painted over yet.
{{gwi:201}}

This leaf has had a couple months to cure. Would a couple coats of polyurethane help?

Part of the problem could be the weakness of your mixture. If the mix sets up too soft it'll nick easily.

Poly might help protect it, but not much will stop the nicking. Why does it get nicked, is something bumping it?

Next time you make some, try thickening up your edges a bit, and make your mix a bit 'stiffer', not so runny. That might help, but with narrow edges, the mixture is likely to be compromised anyway. Your leaf is very pretty tho!

Pesky, I think you are probably right. I have to watch myself about mix not being stiff enough. I don't have any idea how it gets nicked. I have moved it several times to different light to see if I like the coloring. Thanks for your response. Marie