Testing Times

摘要

In his book on ceramic research, Les Glacures Ceramiques: Methodes de Recherche, Marc Uzan uses a base glaze of feldspar [nepheline syenite] plus various fluxes as a starting point to test the properties of glazes. Using the addition of china clay and silica as variables, tests can be plotted on a graph. In this study he has chosen to plot the increasing china clay [kaolin] along the horizontal [X] axis and the silica additions on the vertical [Y] axis. There are 54 starting base glazes using various combinations of nepheline syenite, whiting, barium carbonate, zinc oxide and two borax frits. These are organised in a systematic way to cover combinations of the alkalis and alkaline earths within the unity formula. For example tests 1 to 6 explore the molecular proportions between potassium and sodium oxide (KNaO), calcium oxide (CaO) and zinc oxide (ZnO):No KNaO CaO ZnO1 0.5 0.52 0.45 0.45 0.13 0.4 0.4 0.24 0.3 0.3 0.45 0.2 0.2 0.66 0.1 0.1 0.8Obviously each base glaze, without any china clay or silica additions, is at the 0,0 origin of the graph. All of the 54 sets of tests are recorded at cone 8, 9 and 10 and the results graded for three qualities; shine, transparency and crazing [see Figure 3]. These visual keys are combined on accompanying graphs to produce a graphical representation of the tests as, for example, the results for number 24 at cone 9 [see Figure 2]. Details of the base glaze are provided; the unity formula to the left and the recipe on the right.