Powder

Setting up a glaze from powder for Dipping or Spraying

Wearing a suitable mask, sprinkle the glaze powder into a suitable container of water and stir thoroughly.  Leave to settle overnight and pour off surplus water.  Stir, sieve through an 80 mesh or finer sieve, then add water if necessary to achieve the desired consistency.  This depends upon the porosity of the bisque ware but will be around 880-1230 gm of powder to 1000 ml of water. Lead Bi Silicate Frit based glazes will require less water – 1230gm to 1000mL and stoneware glazes with Ball Clay and or Bentonite in their recipe will be on the lower side at 880gm to 1000mL of water.

When some liquid glazes settle out, particularly over a long period of time, they sometimes set hard at the bottom of the container, making them difficult to re-mix.  Others may settle during use and consequently demand thorough stirring or agitation during the dipping session.  To correct this defect, a flocculant or ‘anti-set’ solution should be added a little at a time, (see Epsom Salts solution recipe below) stirring it in very well until the settling stops.  Add carefully or the glaze will dry slowly on the ware and may cause ‘mud cracking’ and perhaps ‘crawling’ during firing.  The opposite effect of settling is when the glaze appears like thin custard and has a ‘creamy’ feel.  The glaze dries slowly on the ware or peels off during drying.  Some glazes that have a high clay content, or raw zinc oxide, magnesium carbonate, talc, etc., or have had excess dosing of ‘anti-set’ will have this defect.  The cure is to add very cautiously, small quantities of a 10% solution of Soda Ash or Sodium Silicate, stirring well, until normal drying and behaviour occurs.

Application of a prepared glaze:

Use either a bucket or glaze wok.  The type of glaze and the effect desired will indicate how the ware should be dipped:  transparent glazes should be thinner than opaque ones so dip once only.  A rutile glaze may be dipped once or twice for varying colour effects.

Walker Ceramics dipping glazes are delivered with a litre weight of 1500-1750 grams/litre (Specific Gravity (SG) of 1.5-1.75) depending on glaze composition.

Litre Weight bottles are available to check your litre weights – Code HC80

Used to calculate accurate litre weight measurement when mixing casting slips and dipping glazes.

It is supplied with a simple conversion chart and also a method to test the accuracy of your scales.

Litre weights can be checked between 1380 and 1775 gm/L.

Adjusting the glaze to a slip suitable for individual preferences requires the following:

Essential: Dispex, Epsom Salts, volume measuring container, scale with 1 gm tolerance.

Optional : Ford Cup #4 or Paint viscometer (purchase from professional Paint Shops – Brand: Wagner), stop watch.

Procedure:

Adjust the litre weight to between 1400-1500 gm/litre (Specific Gravity of 1.4 – 1.5) by adding clean tap water to the slip.

The glaze slip should have the viscosity of evaporated milk or slightly higher.

If glaze slip is too thick, add Dispex (Product Code CB80) drop by drop until viscosity is satisfactory.

Never add water once you have Specific Gravity correctly adjusted!!

If glaze slip is too thin, add Epsom Salts solution drop by drop until viscosity is correct.

(To make Epsom Salts solution, mix 300 gm of Epsom Salts with 1 litre of hot water.)

It is highly recommended to use a Ford Cup or Viscosity Cup and aim for run-out time of 15 to 20 seconds.

After application the glaze layer should be as thick as the diameter of a standard steel paper clip.