Powdered Glazes, Colours & Frits
- These notes apply to all powdered glazes whether earthenware, stoneware or porcelain.
- Sprinkle the powder into a suitable container of water, stir, then sieve through an 80’s lawn or finer.Leave to settle overnight and pour off surplus water.
- Stir, then add water if necessary to achieve desired consistency which depends upon porosity of biscuit ware but normally will be around 18 - 25 ozs. of dry glaze per pint of water (800 - 1250gms per litre) i.e. about 1kg per 1.4 - 1.9 litres water.
Settling is not normally a problem with Stoneware glazes but may be troublesome with some earthenware or Artistic glazes, the glaze settling into a hard deposit at the bottom of the containers which is difficult to reconstitute. The addition of 1% of Bentonite (3411) to the glaze powder prior to preparation will help prevent glazes from quickly settling and such addition is therefore common practice. Even so, this may have little effect on any tendency for the glaze to set hard once it has settled. A flocculant such as 3415 Calcium Chloride or 3442 Magnesium Sulphate added to the glaze will, however, have the effect of causing the glaze to settle in a more loosely packed arrangement of the constituent parts which are then more easily reconstituted. The method is to mix a little of the flocculant with hot water in a cup until no more can be dissolved. Leave to cool and then add a few drops only of the liquid per litre of glaze, followed by thorough mixing. Larger additions will cause the glaze to thicken (this being helpful if very vitreous pieces are to be dipped).
Once the correct glaze consistency has been achieved it should be measured so that it can be repeated next time. Weigh exactly 100cc’s of the mixed glaze and dividing the resultant weight in grams by 100 to obtain the specific gravity.Alternatively one pint can be weighed to determine the ‘pint weight’. A popular method is to use our glaze hydrometer (ref 5828) to quickly obtain a reading which can easily be checked at each glazing session & the glaze adjusted if necessary