Sentry,
Shermans were generally coated with white wash as ad hoc winter camo. The US Army did not really plan well for fighting during winter and snow camo was in very short supply. My method for reproducing the rapid wear of this kind of camo was as follows:
1. prime and base coat finished model in oil based paints.
2. do some undercoat weathering (to simulate wear prior to winter)
3. paint on Tamiya acrylic flat white in light coats using small brush strokes to simulate a 1/35 tall person painting the thing by hand with a brush or mop.
4. allow to dry.
5. Using denatured alcohol, swab small amounts onto the camo in areas likely toreceive heavy wear and tear.rub the areas with the swab until the paint leaches away. Be mindful the swabs don't hold much of the removed paint before it starts smearing.
6. Once you're satisfied with the heavy wear, use a toothpick doused in denatured alcohol to "chip away" smaller areas of the camo.
The great thing about the denatured alcohol is it will not affect the undercoat. it will only thin and weaken the alcohol based acrylic camo coat. Here's a couple pics of the finished effect.
Note: Similar results can be achieved by using a masking solution prior to the white wash and then rubbing the masked areas clean once the camo dries.
