Feldspars, the primary high temperature flux, melt less than you think.

Our melt fluidity tester is being used to compare cone 8 melt fluidities of Custer, G-200 and i-Minerals high soda and high potassium feldspars. Notice how little the pure materials are moving (bottom), even though they are fired to cone 11. In addition, the sodium feldspars move better than the potassium ones. But feldspars do their real fluxing work when they can interact with other materials. As a demonstration of that, note how well they flow with only 10% frit added (top), even though fired three cones lower.

Related Pictures

Downloadable 3D model for melt flow tester block mold

Available on the Downloads page

3D rendering of Fusion 360 drawing of glaze melt fluidity tester

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

This is a 3D rendering of our melt fluidity tester. We have promoted this device for many years as an effective way to compare fired glaze properties (e.g. melt fluidity, surface tension, bubble retention, crystal growth, transparency, melting range, etc). Open the 3MF file in your slicer, move all pieces off the print bed and unselect them all. Then, print each part by moving it onto the bed and using place-on-face to orient it right. Print the funnel wide-side down with brim. Insert the natch clips and embeds into the holes, pour in the plaster, let it set and finally remove the PLA with a heat gun. You now have a working mold to make slip cast testers. Glue the natches and spacers into the embeds, strap the mold together, glue in the pour spout with slip and finish by filling the mold with slip. If the mold is dry, 10-15 minutes should be enough to get adequate thickness (don't make them too heavy). With 0.8mm thick walls, this drawing 3D prints quickly and is easy to remove when the plaster has set (using a heat gun). The halves interlock using natches (requiring our embeds and related parts). The mold halves can also be lined up by the outer edges before clamping them together (thus not requiring natches).

Videos

Links

Articles	Low Budget Testing of Ceramic Glazes There is more to glazes than their visual character, they have other physical properties like hardness, thermal expansion, leachability, chemistry and they exhibit many defects. Here are some simple tests.
Articles	A Low Cost Tester of Glaze Melt Fluidity Use this novel device to compare the melt fluidity of glazes and materials. Simple physical observations of the results provide a better understanding of the fired properties of your glaze (and problems you did not see before).
Materials	Soda Feldspar A feldspar having a KNaO content that predominates in sodium.
Materials	MC Na-200 Feldspar
Materials	MC 200K Feldspar
Materials	Feldspar In ceramics, feldspars are used in glazes and clay bodies. They vitrify stonewares and porcelains. They supply KNaO flux to glazes to help them melt.
Materials	Custer Feldspar The most common potash feldspar used in ceramics in North America. While having been a standard for many decades its supply appears in doubt in 2024.
Glossary	Feldspar Glazes Feldspar is a natural mineral that, by itself, is the most similar to a high temperature stoneware glaze. Thus it is common to see alot of it in glaze recipes. Actually, too much.

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