Marty McQuirk wrote a great how-to article on this product in the October 2001 issue of Model Railroader. It's a system that allows you to paint PLASTIC to make it look like weathered wood.
I just received my paints today including the fiberglass brush.
Has anyone here tried it? This is similar to the wood stains that Foquil has since discontinued. One paints the gray first and then adds other wood colors on top if desired. The fiberglass brush removes some of the outside finish and blends the colors together for a very realistic effect.