He could have very well used a variety of effects. In all honesty, there are a plethora of methods you can try. They all fall into only two categories:
- Paint the basecoat colour, then when fully cured, overpaint with the top colour. Using a variety of methods you can achieve chipping:
Salt Method
After your basecoate is fully dry, you can wet specific areas of the model slightly, focusing on high traffic areas, then spread salt over them. The salt will bind with the water, and stay pretty static. Allow it to dry like that. Paint over it all with the top colour. When finished, take the salt off, and bingo, you have your chipped paint. A member here posted a Marder III build about 2-3 years ago. I can’t remember who it was exactly, but it was the BEST example of the salt method I’ve seen.
Masking medium
This is pretty much what it sounds like. Similar to the above method, but less tedious. Use a masking medium instead of salt to apply areas that will be your ‘chipped’ paint. Overpaint with the top coat, and then remove.
Thinning/destroying top coat
This is kind of a difficult technique to get to work correctly. You want to use acrylics for your base coat. Allow it to cure fully, so a few days. Then use enamel paints for the top coat. When the paint has dried, but not cured, spread white spirit (thinner) over it, sparingly and carefully. Work only one panel at a time. The thinner will begin to eat at the paint. You’ll see it start to wrinkle. Take clear packaging tape (selotape) and apply it to the panel. You’ll want to apply the tape first to some cloth to take the tackiness away. Section by section, pull the top coat off, and you’ll effectively be performing the same task as nature.
The second group of methods works best when used in combination with one another. They all esentially dictate that you paint your paint-chips on top of the yellow (or whatever other colour) camo.
Brush
Exactly what it says. Use a brush, albeit a very very fine tipped one, and work slow. Less is more (trust me, there are many models that I wish I could retract my steps a bit). You can use the panzer gray, or an very very dark gray. You can also use very dark greens, or very dark browns to portray scratches.
Applicator/Sponge method
Don’t recall where I read this, but I use it as my starting point always now. Take a dish washing sponge, and cut it up into small cubes or irregular shapes. What you’re interested in using is the scrubbing pad (the dark green, abrasive part of the sponge). Pour some of your ‘chipping colour’ into a container. Dip the green part into the paint, dab most of it off on a piece of cloth or paper towel, then start laying it on the model, again focusing on areas of high traffic wear.
There is one more key technique to be used with chipping paint. Its called a filter. Basically, when you apply paint chips, it won’t look natural, there’ll usually be a lot of contrast between the two colours. You want to bind and unify them together. You’ll want to chose a mutually complementary colour (I most often use dark browns) and thin it drastically. You’re looking at 5% paint, and 95% thinner. Then apply it over the entire model, but don’t let it pool. After fully dry, you can repeat as desired. You’ll notice that the paint and chips will look more subdued now. This is also a great technique for unifying camo colours.
Anyways, give it a shot. It won’t be perfect the first time, but you’ll get the hang of it.