We are very lucky to have a thriving grape vine in our garden, which this year is heavily laden. Perhaps unusually for this country, the grapes do ripen, though they are small and slightly bitter to taste. Whilst they can be a little challenging on their own, they combine with apples and blackberries, also form the garden, to make a mean mixed fruit jelly! Not by me, I hasten to add...
But what does this have to do with violin making? In his book 'I "Segreti" di Stradivari' (The "Secrets" of Stradivari), Simone Sacconi argues that the early Cremonese makers treated their wood prior to varnishing, and that the purpose of this treatment was to harden and strengthen the wood, a process he called ossification. The ossification process makes the wood more durable, and enables it to be carved proportionally thinner for the same overall strength. Of course that would also affect the vibration characteristics of the wood, and enable a much lighter and therefore more resonant structure to be built.
Sacconi tells us that the substance used for ossification contains a high level of silica, in other words it is a glassy type of substance, which he identifies as a silicate of potassium and calcium. The old method of producing this substance started with the melting of charcoal and potash in a sealed crucible silica, the potash being derived from the ashes of the green growth of the grape vine or the ashes of the discarded grape pulp. There are historical references to the use of this type of silicate in the art world going back to medieval times.
Sacconi's hypothesis is based on a long career as a maker and repairer working on, and therefore examining first hand, a staggering number of old Italian instruments. He is therefore ideally placed to draw conclusions.
In there internet enabled days, ready made Potassium Silicate and Calcium Silicate are easily available, and you will not find us burning strange mixtures in sealed crucibles in the middle of the night. Apart from anything the Mixed Fruit Jelly is far too good for that!