'Bloom' on laser cut alloys

[Aspman]

Last couple of times I've cleaned my wheels I've noticed a couple of patches (10-15mm across) on the surface of one of them. It looks almost like mould.

I assume it's actually oxidation. I can feel at the centre of some of the patches small scratches or tiny chips just a couple of mm.

 

Are laser/diamond cut alloys coated in lacquer? Wondering if some mild abrasive or polish would remove it.

 

I've actually got alloy insurance but it only covers kerbing. I suppose eventually I'll clip a kerb but meanwhile is there a non-invasive fix?

 

I'd put some clear acrylic on it or something similar if it would stop it spreading.