The current fashion in violin making is to make a new instrument that looks 300 years old. Some folks are really good at it, many are not. The current fashion is really an old fashion, since one can find factory instruments 100 years old that have a factory antiquing underneath a real antiquing.
Part of the problem is that the use of the fiddle has changed over the centuries, with the addition of chinrests, shoulder rests, good quality cases and such. What people want is a violin that looks like it was abused in a normal way -- varnish wear, rounded corners, worn edges, repaired cracks -- but that is actually in good physical shape. Oh, and don't put any scratches on it after you finish antiquing it.
There are various methods for creating wear marks, but the most successful seem to be a somewhat accelerated schedule of normal wear. Here's one method for antiquing the back of the scroll.
Ok - so that was a bit of a joke. I found the photo while looking through a Flickr site whose user name is "sonobugiardo."
But it's not far off. Some antiquing techniques literally consist of rubbing the instrument across the chewed up surface of a work bench. Here's a story I heard from a relatively high-end maker and I think it might be true. He was at a friend's house with a newly made violin that he was in the process of antiquing. His friend's young son had a remote-control toy truck that the kid was showing off by maneuvering it through the dug up, yet-to-be-landscaped, backyard. The idea came up to tie the violin to the back of the remote-control truck and let it be dragged across the ground for a while. It's one way to come up with random scratch patterns.