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Zero3 K Cone 04-02 Transparent Glaze

Zero3 K Cone 04-02 Transparent Glaze


This glaze was originally designed to work with the Zero3 engobe, stoneware and porcelain (fired at cone 03). It is about firing a little higher (cone 03) to get a lot better strength and durability. It also works well on L212, L215. No common middle or high temperature glaze can compare if you are doing underglaze decoration, the brightness and clarity of color are stunning!

Process Properties

Screening: We have not ball milled this product, thus it may contain some oversize particles from the constituent materials. We advise sieving the glaze slurry to at least 80 mesh.


For stronger ware we recommend firing cone 04-03. Every cone higher you can fire will dramatically improve ware strength. All low fire bodies and glazes can easily tolerate firing higher. The chemistry of this recipe produces a more durable glass than commercial cone 06 glazes (they sacrifice hardness and durability to melt at a lower temperature).

To get the best defect-free surface please consider using a hold-rise-drop-hold firing schedule. For 04-03 consider using the PLLFDS schedule.

If you do not need strength and must fire lower (e.g. cone 06), then don't use this, use a commercial product.


This glaze is more sensitive to thickness than most stoneware glazes. If too thin it will not be smooth, if too thick it will run during firing. Be sure that ware has been fired to the temperature for optimal porosity for glazing. If bisqued too high ware will not be absorbent enough for the glaze to stick in a sufficiently thick layer. Conversely, if ware is bisque fired too low or ware is immersed too long during dipping, the glaze will go on too thick and run during firing. If you are brushing consider just two layers. Whatever you do, we recommend a test firing to verify. Keep good records of your bisque temperature and maintain the glaze at the right specific gravity and viscosity.

The body is Plainsman L215. There is good reason to fire to cone 03 instead of 04. The underglazes work the same. The clay is stronger and a deep red color. But best of all, the glaze is more transparent because it has fewer micro-bubbles suspended in the glass. Cone 03 is also more tolerant of getting the glaze on too thick, at 04 will will turn completely milky.

If you want a crystal-clear glaze on L215 there are two important issues: thickness and temperature. Normally, when the layer is too thick the clear glass turns milky (being filled with micro-bubble clouds). So you need to learn to apply it thick enough that it feels smooth (you cannot feel any of the sand particles in the body) but thin enough that it does not go cloudy. The mug on the left was double-dipped and bubbles are visible in the handle recess, thumb-hold and along its edges. But why has the glaze not gone completely milky? Because it is fired at cone 03 instead of 06 or 04.


As of June 2017 it is not yet available as a premixed product. But you can mix to yourself. For our lab information on the recipe, how to mix and use it click here.

Zero3 Clear glaze with stains for primary colors, brown and black. These are 10 gram balls that have been melted down onto a tile (they thus show it very thick). The tiny bubbles are not present on glazed ware (especially if 2-3% zircon is added).

Primary color stains in G2931K

In the above images, the stains have been mixed right into the clear glaze powder to get the six primary colors. Using these primary colors you can blend almost all color you want. Lighten any color by diluting with the clear.

Thermal Expansion

Low fire glazes are more difficult to match to the body and crazing and shivering are much more common than at higher temperatures. Please check this page for recipes of versions of this that have higher and lower thermal expansions if this does not fit your clay body (or fit is affected when you add zircon (for white) or stains for color.


Zero3 Porcelain mug fired at cone 03 in 3 hours. Notice how ultra-clear the Zero3 K glaze is over the underglazed areas. No micro-bubbles. It is applied in a very thin layer. By Tony Hansen.

Zero3 Stoneware mugs decorated with underglazes and finished with G2931K ultra clear glaze. By Tony Hansen.

Buffstone and L215 with underglaze decoration and G2931 weigh-and-mix-yourself clear dipping glazes. But they are not the same. The G2931L glaze (left) has a lower thermal expansion (to slow crazing on Buffstone). The G2931K glaze fits L215 because the latter contains some talc (which raises its expansion). The L215 mug has survived a 300F-to-ice-water thermal shock without crazing or shivering. If you switch the glazes the Buffstone mug would craze it and the L215 would shiver it off in flakes.

L212 underglaze decorated mug fired at cone 03. Outside glaze is G2931H clear. The liner glaze is Crysanthos SG001 white.

Zero3 Porcelain, Zero3 base glaze with 10% inclusion stains and 2% zircopax added (the zircopax is needed to prevent micro-bubbles and surface dimples). The liner glaze is Zero3 K transparent.

Buffstone, L212 and L213. Each has its own clear glaze. G2931L, G2931K and G2931H.
L is low expansion (for zero-talc porous bodies like Buffstone). K is intermediate (for moderate-talc bodies like L215, Zero3 stoneware and porcelain). H is high-expansion (for higher-talc bodies like L212, L213).

Safety Data Sheet

Click here for web view.

Logo Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508