Today I had a client in with a violin in need of gluing. While that in itself is nothing notable, there is an aspect of this encounter that may qualify as a teaching moment, especially apropos to those of us in the Northern Hemisphere who are heading into the heating season.
Violin family instruments are put together with hot hide glue, which has unique properties that are particularly advantageous in some circumstances. I’m not a “science guy” so I can’t answer questions about crystalline structure or tensile strength as opposed to other kinds of strength. I do know, for instance, that drywall screws have incredible holding power unless you whack’em sideways with a hammer, and for some reason, I am reminded of this when I think about violins and hide glue.
Hide glue, made from animal byproducts, is essentially the same stuff that’s been used for hundreds of years in the assembly and repair of violin family instruments. The remarkable characteristics of this adhesive include its strength and its weakness. We have a wealth of instruments with top and back center joints that have retained their integrity for hundreds of years. Be thankful. Then we have the treble side upper bout and the lower bass side seams that, on so many instruments seem to open up on a regular basis. Again, be thankful.
Wood moves seasonally, especially here in New England. In moist weather, it swells. In dry weather it shrinks. Plain and simple. In my house here in Holyoke, the oak floors creak in the winter and in the summer, I can’t close the doors on the antique cherry corner cupboard without risking not being able to open them again until October. In my last house, the oak floors in my living room developed summer speed bumps that would have been the envy of any gated community.
An instrument seam glued with hide glue will break apart when stressed. This is a good thing in mid-winter when the heat’s been on and the wood shrinks. It’s preferable to having the wood itself crack. Having open seams glued is a normal part of violin/viola/cello maintenance. This characteristic of hide glue is also the reason that it is even possible to disassemble an instrument to do interior repairs. So we’re thankful, right?
That said, if a violin maker/restorer is smart, and skillful, he or she will take advantage of the properties of the materials at hand, in this case I’m considering the glue. Hot hide glue can be mixed in ways that varies its strength. A fresh pot of glue will be strongest. With repeated heatings, its strength diminishes. The strength can also be altered depending on the proportion of water used in the batch. Theoretically, one would be very smart to use the strongest glue, say, for the center joints in the top and back, for setting the neck joint, and for joining fresh cracks. It may be smart to use a weaker glue mix for securing the fingerboard, and assembling the top, which could be subject to seasonal stresses. Remember, an open seam is preferable to a crack.
Speaking as a restorer, we like the fact that hide glue is reversible. It may seem counter intuitive, but the reversibility of hide glue actually increases the chance that an instrument will live a very long life.
Back to my client, who was smart to call in an emergency. She was concerned with the lower block area of her violin, which looked like this (violin is viewed with the back up, so we can see the area where the tailpiece is anchored by the end button):
Indeed, the glued seam had released, but in this case, the loose seam extended over the lower block, leaving the body of the instrument vulnerable to the longitudinal string tension. I suspect that the end grain of the lower block was improperly sized on this relatively “new” instrument, before the top was glued on, causing the area to separate.
One can see from the photo how the string tension has compressed the body from end to end, and the button/rib assembly has abandoned the original glue line. The lower block is no longer secured to the top, and the spruce top is now bearing more than its share of structural tension. Not a good scenario, structurally speaking, BUT one that is easily remedied at this stage. When I loosened the string tension, my client and I both heard the lower rib/block area pop back into place.
This story ends with a simple gluing and a happy violinist! The moral of the story is that all open seams are not created equal. This particular seam opening demanded immediate attention due to the structural issues it presented.
restorersmind 