[DustyPorViva]

Well I consider a layer just putting an invisible paper over a picture.
You can draw over it and not mess up what is under it.
Of course in MSPaint that feature is useless since it isn't permenant.

Well I did a kind of step by step of the texture I did:

Basicly, I did a random kind of cross lining.
As I carried on I added random dithering to help fill space whilst maintaining a good texture.
Some times adding light pixels to the darker sides help give the feeling of the rock actually coming out and catching some light.