Test Code-numbers All Tests

GLAZ - Glaze Observations Test

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.

Measure specific gravity using a scale and measuring cup

This picture has its own page with more detail, click here to see it.

The specific gravity of a suspension is simply its weight compared to water (water weighs 1g per cc). For example, different glazes optimize to different specific gravities (e.g. 1.45 is typical for stoneware glazes). Casting slips typically have specific gravities of 1.75-1.8. This plastic measuring cup accommodates 500g. I have already counter-weighed it on our 0.1g scale and filled it with 500 grams of water to verify the accuracy of the 500g marking (mark the correct level with a felt pen or sticker if needed). Now, I am filling the cup with the slurry to the same level. The specific gravity is this weight divided by 500.

Variables

Initials of person making observations

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.

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).

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.

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.

Wash 100 cc of the glaze through a 325 screen (44 microns), dry and weigh the residue.

Related Information

Links

By Tony Hansen Follow me on

Got a Question?

Buy me a coffee and we can talk