From David D McClelland:

Re: Secret of the great violins? The wood, study suggests (July 1): My hobby at this time is fixing old stringed instruments. I have run across 3 different Strad copies, the oldest being somewhere at the beginning of the 18th century (looks like 1717). Not only is the wood more closely grained and even, it is much more pliable due to a secret (to me anyhow)chemical treatment. It has been suggested to me that it was treated with a leather tanning solution. Who knows??? Density and uniformity, yes, but there is much more to it than that I suspect.