I bought the gun from Electrostaticmagic and asked them the same question. They said thickness should only be 7-9 microns (1000ths of a mm) and this has been borne out from my testing.

They also supply the powder.

I looked at the "Wet" methods online and decided against it. From what I saw you often end up coating them twice and messing around with acetone didn't appeal either.

The gun works really well and produced perfect results first time of use. Of course you need a small compressor but definately worthwhile.

https://www.electrostaticmagic.co.uk/