Glaze Observations - GLAZ
This test procedure was employed in the Foresight Ceramic Database and now is available for those having an account at Insight-Live.com. Accumulating test data using the variables defined in these procedures enables us to create tools that enable you to compare the physical properties of materials and recipes.
This test could be used maintain the slurry and fired properties of a production glaze. It does not require advanced equipment and produces a set of numbers that can quickly be compared with another batch or day. First accumulate a history of measurements and relate these to other events to identify the best consistency and what measurements are associated with problems. Then establish a specification that will be the target for future batches of this glaze (other types of glazes will likely have their own specifications). The result will be consistency and alarm bells when numbers fall outside the acceptable range.
DATE - Date (V)
INIT - Initials (V)
Initials of person making observations
VISC - Viscosity (V)
Viscometer drain time in seconds (i.e. a simple 60 cc veterinarian's syringe can be used; fill it to the 60 cc mark and time the drain to the 10 cc mark.
SPGR - Specific Gravity (V)
Weigh 100cc of the glaze and divide the result by 100. Or use a hydrometer if the glaze is fluid enough to allow it to bob up and down and it has a scale designed to measure in the target range (e.g. 1.3-1.6).
VISC - Value (V)
Viscometer measurement (i.e. a simple 60 cc veterinarian's syringe can be used; fill it to the 60 cc mark and time the drain to the 10 cc mark.
PH - pH (V)
Dip the pH meter probe in the water at the top before mixing the glaze in the morning (or extract a water sample by filtering). Use pH paper if you have not meter.
O325 - 325 mesh residue (44 microns) (V)
Wash 100 cc of the glaze through a 325 screen (44 microns), dry and weigh the residue.
Specific gravity of a glaze using a scale and measuring cup
The specific gravity of a glaze slurry is simply its weight compared to water. Different glazes optimize to different specific gravities, but 1.4 to 1.5 is typical (highly fritted glaze are higher). To measure, counter-weigh a plastic measuring cup on your scale and fill it with 500 grams of water and note how high the water fills it (hopefully to the 500cc mark!). Fill the container with your glaze to the same place. Divide its weight by the number of ccs (in this case, 500) and you have the specific gravity. The more you weigh the more accurate is the test.
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