Looks epic!
The powders will disappear at an alarming rate if you spray them with varnish, I think mainly because it blows away from the pressure but potentially because some sort of reaction fades the colour as well.
Some of the effect does remain but it’s still annoying. I would try it on a small bit and see what you think, you might want to fix the powders in a different way first, like soaking it with watered down glue or alcohol from a pipette.