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Discussion Forum - Instruments - Thread
paulnviolin
Paul N.

Why violins (and other string instruments) are not varnished inside?

February 20, 2026, 9:01 PM · I am making a custom table desktop with metal legs and wood tabletop and also a custom long cabinet below the TV, also made of hardwood, and while in the store and reading all over the internet, "everyone" says you need to varnish the wood all around, not just the top or visible parts, because if you only varnish one part, the humidity will not be compensated and you will have all kind of problems in the long term, unless you are lucky and somehow your furniture moves withing the limits of cracking.

So... I was thinking... why don't luthiers varnish the insides of a violin so the wood is uniform and absorbs or exchanges with the outside the humidity at the same rate in all the areas?

Replies (5)

manfio
LUIS CLAUDIO MANFIO
February 20, 2026, 9:10 PM · Sacconi, on his book "I Segreti di Stradivari" mentions that Strad covered the inside of his instruments with a "composto isolante", that he called "vernice bianca" (white varnish), a mixture of egg albumin, sugar, honey and water.
Some makers do some inside treatment.
BenTX
Ben Furman
February 20, 2026, 10:35 PM · According to Bob Flexner, shellac is the best moisture barrier, so I can imagine a thin sealer coat would be helpful in controlling the rate of swelling and contraction. Might need to avoid the glued areas to avoid adhesion issues though.
cottonmather
Cotton Mather
Edited: February 20, 2026, 11:46 PM · shellac is not an effective barrier against moisture, at least over an extended time.

I lightly treat the inside of my violins with a very light coat of colophony, followed by shellac. I don't believe this makes the instrument completely resistant to atmospheric changes, but I think it does help somewhat.
putting a full coat of varnish on the inside of the instrument would damp the plate too much, and it wouldn't serve any real practical purpose. the main function of the varnish is to protect the wood and to look pretty.

lafoca
joel quivey
February 21, 2026, 1:27 AM · It is hard to put the brush through the f-holes.
SDGagliano
Stephen Symchych
February 21, 2026, 4:49 AM · That is why Tony and the boys used Dust Busters in reverse gear.