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There are two main types of varnish; oil varnish and spirit varnish.
Virzi Tone Producer
The Virzi Tone Producer is a thin (perhaps 3/32"), oval piece of wood (straight-grained spruce or fir) which is mounted inside the body cavity of a mandolin (or mandowhatever, or guitar, or violin), suspended directly below the bridge and attached to the top of the instrument by a pair of 'feet'.
After leaving Gibson, Lloyd Loar started the ViviTone company with the purpose of producing pianos and stringed instruments.
Vega distributed their mandolin family instruments between approximately 1913 and 1925.