[Jewelry making - Article 00309] - [Orchid] Shellac - Caustic soda

[John Burgess]

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    G'day The action of caustic soda on shellac is simply to soften it so
    that it may be easily scraped away.   When applied to paint, it
    reacts with the fatty part of the paint, allowing the remainder to be
    scraped off. Caustic soda is not normally included in the term
    'solvent'. When it makes things "disappear" like meat, for instance,
    it reacts with the fat and forms a soap and glycerin.  Contrary to
    popular belief it does not 'eat' bone.  It simply removes all the
    fat, leaving the mineral part of the bone, which is how laboratories
    prepare skeletons for display and study, and how bone carvers prepare
    their work specimens. The reaction between organic materials and
    caustic soda can be quite violent and it destroys part of the
    structure. One of your correspondents suggested that caustic soda was
    thrown into pits containing bodies. I suggest that this was not
    caustic soda but quicklime (calcium oxide) which removes water from
    the body, then the alkaline material slowly disintegrates. Chloride
    of Lime (calcium hypochlorite) was used for the same purpose, and in
    this case it acted as a bacterial deterrent, so smells and bacterial
    reactions could not occur. 

    To prepare shellac for use, it is common to simply pour a little
    ethanol or methylated spirit into a jar containing some of the flake,
    covering, and just leaving it overnight. Further meth spirit can be
    added later if needed. 

Cheers for now,
John Burgess;   johnb AT ts.co.nz of Mapua, Nelson NZ

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