Roughly 10 years ago I was looking at a way to simulate dirt,mud and rust that did not just look like a glop of paint. Inspired by some anime models that I saw on the web I looked for weathering powder and I found Tamiya had a product line of powder and sticks so i look for other products that i might be able to get for a little less cash and came up with some of my own powders
ok so there are three thing you need to do this if you want to make your own.
1: A cheap small strainer don’t use your mom’s or your wife's it will damage it.
2: Something to to hold and store the powder.
3: the medium that you are using.
First I use compressed pastels for the powder make sure it is not oil based as it will be more of a paste.
Second one is a compressed charcoal stick.
to make the powder is pretty much straight forward.
Take the strainer put it on top of your storage container (less loss this way)
and rub the stick over the strainer keeping it close to the center and watch some TV took me about 20 min each stick.
When you are done you should have a powder of the color you just did.
There are a good assortment of of colors available and you can blend you own colors from the powders you make have fun and be creative