Making weathering powder

The hobby industry, as we all probably know, operates in a very competitive market. And as such, each manufacturer is trying really hard to come up with new & exciting products for us hobbyists to buy. But quite a few of those products are a bit of a con i.e. Clump foliage, Basing material, Gravel....for christs sake! and Weathering powders. About five or so years ago when weathering powders hit