One of my Flickr contacts commented on my photos, posted in this blog yesterday, mentioning the rust marks in the old 2x4s, something she thought might not be pertinent to violins. Her argument that (1) a bathroom wall was periodically very humid, and (2) it contained nails -- unlike violins.
Well, it reminded me of a couple things that many violin makers know, but which might not be common knowledge among normal, non-violin-obsessed folk.
First, the violin (and the viola) actually is subjected to fairly humid conditions. The player is breathing right on top of the instrument, with moist air from the player's nose sending moisture over the top and in the f-holes. I am an amateur fiddler. Our band played a contra dance last night, and as the fiddler, I get quite a work-out. The dance lasts about 2-1/2 hours, and though I'm not playing the entire time, I do probably get a good 45 minutes to an hour of fast playing.
If you watch videos of the really great players, you can often see that they are putting out a lot of energy. And that's just the performance. Imagine the thousands of hours that go into practice.
So that's humidity.
Now about nails. Modern violins are not made with nails. But in the time of the Amati, Guarneri, and Stradivari, they were. The necks were not mortised into the neck block as they are now. They were surface mounted -- a butt joint -- to the ribs, and nailed from behind (drilled first, no doubt) and the plates were installed afterwards. This method is not as strong, in part due to the differential tensions in the strings. Necks could be pulled to the e-string side over time or fail altogether. The neck mortise solved this problem, and nearly all old instruments have had their necks reset, with the addition of wood to make up the difference.
From the National Music Museum at the University of South Dakota, an x-ray of the neck of a tenor viola built by Andrea Guarneri in 1664.
And from a 1693 Stradivari violin, the rust stains from similar nails that have bled out to the surface.
In the Stradivari neck heel, you can also see an extra piece of wood, just above the ebony crown, indicating a neck reset. That is, that slice of wood was added by a later repair person when working on the instrument. The ebony crown is a later addition as well, being put in place to clean up damage done to the button in, say, a neck reset.
You can see the rest of the Guarneri viola here and the rest of the Stradivari violin here.
Some violin makers might try to simulate this sort of aging and some players might look for it because it has the 'right' appearance.