One technique to paint horses, described among others in Kevin Dallimore’s Foundry book, is the ‘oil wiping’ technique. It involves using dark oil paint (hence the oil part) that is painted all over the horse and then wiped off (and there’s the wipe part) of most of the horse again, leaving the oil paint only in the recesses of the model. This creates an instant realistic shading which is hard to reproduce with more standard techniques.
The two properties of oil paint that are exploited by this technique are its long drying time (if you tried this with acrylics, they probably will have dried on the model before you wiped them off) and the fact that in thin enough layers it is translucent, so you get a sort of blended effect.
The disadvantages of the technique are those of oil paint: messier to clean up (and you shouldn’t really chuck turps or white spirit down the drain, so there’s that problem as well) and it takes a long time to dry. And not everyone has a ready stash of oil paints lying around (they tend to be expensive, too).
So, thought I, Vallejo to the rescue! In addition to the colors themselves, the Model Colour series also includes a few other items, two of which I’ve used to recreate the oil wipe technique using acrylics. The products I’ve used for this are matt medium (540) and drying retarder (597). The matt medium is basically the liquid that carries the pigment in the paints themselves (the paints are, reduced to their essence, a mixture of medium, binder and pigment), and the retarder is a chemical (some glycerine derivative, but I could be wrong there) that extends the drying time of the paint.
These two agents combined and added to normal paint result in the same properties as the oil paint (more or less): longer drying time (the retarder) and slight translucency (more like less covering power really, the medium). As we say in Dutch, tadaa!
To put my pixels where my mouth is, here’s a picture of a horse shaded using this technique. The horse base colour is Flat Brown (984), which was shaded with a 1:1:1 mixture of Dark Brown (822) : retarder : medium. The shade coat was painted all over the horse (literally) and then wiped of with a
peacepiece of tissue. This is the result:
Some of the basecoat has been wiped off where bits of metal protrude from the model (bad cleaning of the model), so I’ll give this a quick drybrush with Flat Brown again to touch up. Otherwise, not a bad result, I’d say.