Painting Mask

[jds 20]

My nine-year-old son has started playing goal and just got his first goalie mask. It is all black and he wants to dress it up a bit with some artwork. A friend is a graphic artist who can do some basic designs but I want to make sure that this is legal (he plays in OMHA) and if anyone has any tips on what to use to do this (airbrushing is not likely an option). This is just a basic design-I'm not talking about the elaborate airbrushed designs that cost hundreds of bucks.

Any input would be appreciated.