Glaze Course - Lesson Summaries
Substituting materials using 'R to F' (Recipe to Formula) in Matrix.
Lesson Number 13
One of the most common questions posed by studio potters is "How can I make use of a recipe which contains materials that I do not have and cannot get?"

Without the capacity to use an analytical approach to this question a potter is faced with long and sometimes arduous blending processes which systematically replace unavailable materials with available ones known to be similar in their nature. Blending is required to try and find the right balance of the new materials thus creating a new glaze which has similar if not identical chemical and fused properties to that of the original.

Typically, of course, a fired sample of the original glaze may never have been seen. The glaze may have been chosen on the basis of a verbal description or a less than desirable photograph. Then again the original glaze will have been applied and fired on a different clay body and under conditions which will not be the same in another geographical location..... so the potter will be assessing the new glaze on the basis of what he/she imagines the glaze should look like.

The best we can do initially is to try and reproduce the chemistry of the original glaze in our new glaze and this is not such a difficult task when we have software such as Matrix. This is after all, one of the prime tasks for which most glaze software is designed.

This week we will look at one way in which Matrix can be used to replace or substitute an unavailable material for one that we have access to. In making this substitution our primary concern will be to maintain the original chemical analysis (unity formula). We will work with the raw materials in the recipe firstly finding a replacement material then adjusting the quantities in the recipe until the unity formulae for the two recipes is as near to identical as we can get.

When we have created a chemical twin for the glaze the new glaze should then be fired. An assessment of the result will then suggest ways in which the new glaze should be manipulated towards the potter's ideal.

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Contact: Lawrence Ewing - 1015 Ellis Rd, Five Rivers, RD3, Lumsden, Northern Southland,
New Zealand