Grid Blends

VOLUMETRIC BLENDING for the "Grid Method"

Copyright © 1998 by Ian Currie

Preparing the Corner Glazes

Firstly we must work out the Corner Glaze recipes for our own set. This can be done in the Corner Glaze Calculation zone, which is at the bottom of the Calculation Page. The recipes for Corner Glazes A, B, C and D are given in a batch size which we determine; the default is 300 grams, which will allow us enough material during the blending of the 35 glazes to produce almost 50 ml. of each glaze.

Weigh out the four glazes. Wet up and sieve the four glazes, being careful not to lose any*, and starting with Glaze A, and not using too much water. Glaze A will usually be the "thickest" of the four glazes (because it contains the most kaolin) and it should be prepared somewhat thicker than we would usually use for glazing bisque. Adjust the four glazes to exactly the same volume. Keeping Glaze A "thick" means that by the time we make up Glaze D (usually the "thinnest") to the same volume, it shouldn't be too thin. For 300 grams of glaze, this will often be around half a litre. [ Note that this does NOT mean add half a litre of water to each dry glaze!] Once this is finished, and the glazes are gently stirred until they are uniform, we have four corner glazes containing equal dry weights in equal wet volumes. Therefore we can now blend by volume and the maths is the same as if we were blending by weight. We can now prepare all the glazes by volumetric blending using the Blending Chart, and if we are accurate and reasonably careful in our technique, then the recipes for the 35 sample glazes will correspond to the recipes given at the Calculation Page.

*In the process of preparing the four corner glazes, try not to lose too much of the 300 grams of glaze. The theory of volumetric blending assumes that we have identical weights in identical volumes. If we lose a lot of one of the corner glazes during preparation, this could affect the result.

Order is important if we are not to become confused or make a mistake. In the blending and the glazing of the grid tiles, lay the things out in the 5 by 7 format. We should orient our copy of the Blending Chart, the 35 cups, and later the bisque-fired grid tiles the same way, with the "A corner" in the "top left corner".

Blending the Full Set

On our work bench, we set out 35 cups exactly as set out on the Blending Chart, in the 5 x 7 format. Write the numbers 1 to 35 on the cups, and also some glaze set identification.
The Blending Chart shows how many ml. of each glaze goes into each cup. Note the key at the bottom of the Blending Chart.

Starting with Corner Glaze A, stir it carefully so it is quite uniform.  This is very important; do whatever is necessary to see there is no glaze settled out. Using a 50 ml plastic veterinary syringe, measure out into each cup the amount of glaze A indicated by the Blending Chart. Repeat for the other 3 corner glazes.

If any of the corner glazes are at all watery, stir the glazes immediately before the syringing process to keep it uniformly suspended. Also don't give the glaze time to settle in the syringe. Glazes C and D will often be a bit watery and settle quickly because they contain no kaolin. THE CORNER GLAZES MUST BE UNIFORMLY SUSPENDED DURING THE SYRINGING PROCESS.

Once the blending is finished, let them stand if possible for an hour or so. Now that the blending is completed it is allowable to add (or remove) water to the 35 glazes to get a good consistency for applying them thickly to the grid tiles. This may mean decanting water off the bottom few rows (low kaolin) and/or adding water to the top few rows (high kaolin). The kaolin functions as a suspender and thickens the glaze. It varies from zero to 40% across the set, and so the glaze water content usually needs to be adjusted after blending and before applying to the grid tiles.