|Monthly Tech-Tip |
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.
The viscosity, specific gravity and pH relate directly to the application, laydown and drying properties. The residue measurement helps identify contamination.
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.
INIT - Initials (V)
Initials of person making observationsVISC - 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.
Simple Clay Evaluation
Glaze Melt Flow - Runway Test
A method of comparing the melt fluidity of two ceramic materials or glazes by racing them down an inclined runway.
Tests conducted on glaze batches used in production (as opposed to tests conducted on the materials used to make those glazes).
|By Tony Hansen|
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