fearthebat wrote: And btw i find that artist charcoal works the best. you get very accurate and RAW results from it. but make sure you have a sealant to seal it in after
Seriously, I second what Matt said, as I use artist charcoal sticks for weathering masks. You can apply the charcoal directly to the mask and blend in with your fingers....or rub the charcoal on your finger tips and rub/blend in onto the mask for a less subtle approach. Works surprisingly well. In the past, I have also used dirt/soil on my rotted masks.
Third for charcoal.
Also, newspaper (the ink rubs off gradually, trust me it adds up (I used to be a shipping director, and we used tons of recycled Newspaper (hands were always near black after work). Obviously the newspaper would be a more generalized darkening agent, while the artist charcoal can be used for fine detail and darker work. Perhaps even a pencil as well. All sealed after applying of course.
Here's a site highlighting how reactive chemicals are with latex (this usually will help determine what's good to use when painting a mask, and what is not).
http://www.primelineindustries.com/natu ... chart.html