Tamiya offers by far the easiest way to achieve realistic finishing effects on your scale models with the Weathering Stick.
Use glue-stick type container to simply "paint" mud or snow onto tank treads or rally car chassis.
With no need for a brush or pallet, Tamiya's Weathering Stick takes modeling simplicity to new heights.
The pen-type Weathering Stick offers up to 5mm of easy-to-apply color by simply twisting the tip.

Weathering means adding realistic-looking effects to your models, such as sand on tank treads and mud-caked rally car bodies.