Ivor and Olive Lewis on sun 28 mar 04
Dear Friends,
Boron, in association with Sodium, forms a water soluble salt called
Sodium Tetra Borate. This is one of the materials used in frit
recipes. If excessive amounts of frit are used in any glaze, without
those necessary stabilising agents recommended by Ron and John, then
we might expect to find some of it will leach when the glaze is
attacked by a weak acid.
How can we find out if that has happened. Go to the Chemical analyst
with your samples.
If you are sure the glaze in question does not contain Barium or
Copper you can make a qualitative test (....We know its there but not
in what quantities....). This is done in a fume cupboard or under an
extraction hood.
Test for Borate Ions.
1 Evaporate you test solution to dryness in a porcelain evaporating
dish.
2 Scrape the residue to the centre of the basin.
3 Add three drops of Concentrated Sulphuric acid and mix well.
4 Add 10 drops of Methyl Alcohol slowly while stirring.
5 Light the alcohol in the dish.
6 An immediate Green Colouration to the flame indicates the presence
of Borate ions.
If in doubt, test a sample of Borax as a comparison.Note that both
Copper and Barium give green flame indications which can mask the
Borate indication.
Best regards,
Ivor Lewis. Redhill, South Australia
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