Drybrushing is the technique of loading a brush, wiping almost all the paint off it, and dragging what is left across a model so it catches only the raised surfaces. It is crude, it is fast, and on the right surface it is close to unbeatable: fur, chainmail, stone, wood grain and heavy texture all come alive in a single pass that takes seconds.
What is actually happening
When a brush is nearly dry, the small amount of paint remaining transfers only where the bristles meet resistance, which on a sculpted miniature means edges and raised texture. The recesses are untouched because the bristles never reach them with enough paint to deposit. The result mimics what light does, catching the parts that stand proud, which is why a drybrushed surface reads as lit rather than merely painted. Getting the amount of paint right is the whole skill, and the usual error is far too much.
Where it works and where it does not
On texture it is excellent. On smooth armour panels and faces it is poor, because there are no raised edges to catch and the technique instead leaves a chalky film that looks exactly like what it is. The other limitation is subtlety: drybrushing is a blunt instrument, and a heavy pass with a light colour over a dark base produces a dusty, washed-out look that is hard to correct. Restraint and building up in several very light passes is how experienced painters keep it looking deliberate.
The brush it destroys
Drybrushing splays bristles by design: you are scrubbing a stiff, nearly dry brush against a hard surface, repeatedly. No brush survives it in good condition, and using a good sable for drybrushing is the most reliable way to ruin one. This is why nearly every painter keeps a dedicated drybrush, usually a cheap synthetic that was already past its best, and why some brushes are sold specifically for the job with short stiff bristles cut flat. Keep it separate from the brushes you care about, because reaching for the wrong one is easily done.
Questions people ask about drybrushing
What is drybrushing?
Wiping almost all the paint off a brush and dragging it across the model so only raised surfaces catch colour. It produces instant highlight on texture.
What should I drybrush?
Fur, chainmail, stone, wood and heavy texture. It works poorly on smooth panels and faces, where it leaves a chalky film instead of a highlight.
Does drybrushing ruin brushes?
Yes, by design. It splays the bristles, so keep an old or cheap brush for it and never use a good sable.