Tojo72:
I was going to post a link,but there are so many of them.
Use the Search Our Community,feature toward the bottom of the forum page.There are many,many posts on the subject.Enter Oil Dot Filters.
You will find some good tutorials
For all the typing, you could have just as easily told him how to do the weathering.
Oils are probably best because they give you the longest working time and blend the easiest. The most important part of this, which I found out the hard way, is to have the correct thinning agent. You need the turpenoid in the white bottle with the blue lettering. The stuff in the white bottle with red lettering, just turns your stuff to mud.
Pick up a few colors of oils, staying away from dark colors (browns and blacks). Blue, red, yellow, white and green give the best results. Pre-wet the surface with clean turpenoid. Add little dots (smaller than a pin head) at various places on the surface. Dip the brush in clean turpenoid and pull down (or in the direction that gravity would pull water). Repeat the pulling process until the individual colors are no longer visible. Clean the brush every few wipes, to keep everything from becoming a uniform brown.
-Fred