[Jewelry making - Article 00145] - Re: [Orchid] Small glass project

[John Burgess]

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G'day;

    In about 3 lives ago I used to be a scientific equipment glassblower
    and quite often needed to cut glass tubing. The standard method for
    lengths of tube or rod is to make a deep scratch with a sharp three
    cornered file, apply saliva to the scratch with the finger, and use a
    pulling-snapping motion, when it would break cleanly. 

    To cut a small piece off the dome end of a test tube almost at the
    end, one can make a deep scratch then apply the semi molten end of a
    piece of narrow glass tube or rod to the scratch. This induces a
    crack, and if the crack is followed round the tube with the red hot
    glass, it will crack right round. For Pyrex tube one made the usual
    scratch then wound wet blotting paper around the tube either side of
    the crack, building up a thickness at least half a centimetre, with a
    gap of about 4 - 6 millimetres between the strips. A pencil pointed
    very hot flame is played on the gap whilst turning the tube, and the
    resulting strain crack will run around the tube following the flame.
    Rubbing the cut end on a sheet of wetted 200 grit wet-'n-dry abrasive
    paper with a circular motion will give you a clean edge. 

    If you need to cut a glass bottle or jar, the simplest way is to
    fill it to a scratch mark with fairly thick motor oil; make an iron
    rod orange hot and plunge it into the oil. The glass will crack
    perfectly. 

    Another method is to take a length of heavy fencing wire (about
    8SWG) and shape an end so it fits neatly round the bottle with no
    gaps. Make the wire red hot and place the bottle in the curve and
    turn it slowly. It will crack at the wire-glass junction. Clean up
    the edge with wet-'n-dry. 

    When in the Navy and horribly ill and seasick I once managed to
    chuck all the mess cups over the ships' side with the washing up
    water. I scrounged oil off the engineers and bottles off the men and
    made a dozen glass cups this way. But I wasn't popular. 

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

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