What finish used on pre 1920 acoustic?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by stormin1155, Apr 27, 2016.

  1. stormin1155

    stormin1155 Member

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    I am rebuilding for a customer what we believe to be a parlor guitar from circa 1915. It has no markings, but the marquetry trim and other features are quite similar to an old Supertone I used to have, so good chance it was built by Harmony.

    My question is, what finish does it likely have? I'm thinking shellac. If it is shellac, am I correct that denatured alcohol would dissolve it?
     
  2. swiveltung

    swiveltung Member

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    My '37 Martin seems to be Nitro.
     
  3. stormin1155

    stormin1155 Member

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    Yes, nitro was developed in the '20s, and I think Martin started using it in the '30s.
     
  4. Laurent Brondel

    Laurent Brondel Supporting Member

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    Before nitrocellulose lacquer most instruments were finished with shellac, or a "spirit varnish" (which is shellac with added gums and resins). Very few actually still bothered to use oil varnish, Gibson mandolins being the exceptions (and probably a few other makers / instruments), but I still think they top-coated with shellac (maybe with the French polish technique).
    Before the 19th century when shellac appeared massively in the West, most instruments were finished with oil varnish.

    Yes, DA is the solvent for shellac.
     
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  5. stormin1155

    stormin1155 Member

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  6. great-case.com

    great-case.com a.k.a. "Mitch"

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    Watch out for some risk when you dissolve the Lac. Not knowing what the wax content is garners my concern. Old Shellacs were nasty with paraffin (check me Laurent, if you please) and this can run deep into the pores if it is not wicked away soon after it loosens on the surface. Do not over apply the alcohol.
     
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  7. Laurent Brondel

    Laurent Brondel Supporting Member

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    Typically musical instruments are (were) finished with de-waxed shellac, it is nearly impossible to achieve a high gloss hard finish with non de-waxed shellac. It is now possible to buy de-waxed flakes, or even de-waxed pre-mixed shellac (Zinsser Seal-Coat is exactly that and is excellent).

    A 100 year old shellac will be quite hard as it typically polymerises a bit with time and becomes more resistant to chemicals. Best is to test with a q-tip dabbed in DA under a tuner to make sure of the nature of the finish. Shellac, even old, is the only finish that will readily dissolve with DA.
     

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