When the purfling is in place the arch can be finished.
The arch serves to add stiffness and strength to the top and to the back, which helps them to support the force of the strings on the body. The height of the arch was set when the plates were roughed out. The low point of the arch is a trough inside the edge, usually at or slightly inside the line of the purfling. As I explained in the last blog, the edge rises above the low point of the arch to provide a bumper for the violin. The trough is carved into the plates with a channel cut using a gouge, followed by finger planes. The thickness of the edge and the depth of the channel work together to produce the desired thickness and acoustic stiffness and flexibility of the plates along the ribs. This will vary depending on the nature of the wood and desired playing characteristics of the finished instrument.
With the high and low points of the arch set, I can shape the arch between the two points. Each maker is usually fairly consistent in what they think a good arch should be and look like, and that will be characteristic of their work when they have reached a mature style. The shape of the arch is one of the factors that give each maker’s work its characteristic sound. A violin with a Strad-type arch will tend to have a Strad-type sound.
The Strad arch in this period of his work is lower than most of the work of earlier makers, but is now considered of average height. The VSO violin has an arching height of 15.5mm on the back and 15.1mm on the top. There is modest scooping in from the edge of the back, and much less scooping on the top. The lines between are fairly straight with just a hint of convex curve. The center cross curve is fairly narrow, but not pointed. The long curves of the top and back are full, but graceful with the top decidedly fuller on the ends than is the back, leaving an elongated straight section in the middle of the top.
In general the higher and more round the arch, the stiffer the plate will be, and the lower and straighter, the more flexible. This can be adjusted to complement the qualities of the wood, and to modify the sound and playing quality: higher-rounder giving a brighter sound and lower-straighter easier response and more depth to the sound.
I shape the arch with finger planes followed by scrapers, and then use sandpaper for the final finish.
The wood for the VSO violin is on the stiff and heavy side, but I have kept the arch to the shape of the original and will make accommodations in the thicknesses of the plates.
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