This one’s interesting mainly because of its lack of great age: it’s from 1944, made in Hamburg, Germany; not a time and place you see many violins from. Usually I would associate this type of mud-crack surface with a soft varnish that’s been overcoated with something much harder (violating the painter’s fat over lean rule), where expansion and contraction of the softer underlayer has caused the over coat to break up gracelessly the way ice breaks up on water, but I’m pretty sure this particular violin has nothing over the original varnish.
In real life the surface of this violin looks leathery; it’s an attractive surface, but better in some places than others. Nevertheless, the whole effect is positive on a violin of a type that you’d normally see polished up like a bowling ball.