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G2934 Cone 6 Matte Low LOI Version

Code: G2934Y
Modification Date: 2018-01-10 15:57:20

MaterialAmount
Ferro Frit 324910.0
Nepheline Syenite10.5
Wollastonite21.5
Talc14.0
EPK20.5
Silica13.0
Calcined Kaolin10.5
 100.00  

Notes

This is an MgO matte. High MgO content is a common matting mechanism at cone 10 but also works at cone 6. This recipe has the same chemistry as the widely used G2934, however this one sources much of the MgO from a frit and talc rather than from dolomite. The benefits are a much lower LOI (3.8 vs. 13.6), a smoother fired surface and better melt fluidity (while still very matte).

This glaze has a very low thermal expansion and will not craze an any common clay body. It accepts stains exceptionally well.

This recipe employs a mix of calcined and raw kaolin to keep the drying shrinkage down (to avoid cracking on drying). If you use pure kaolin it will likely crack during drying.

We recommend doing cutlery marking tests on your ware. If they mark, blend in a little transparent glossy glaze (like G2926B). This will compromise the matteness a little but will reduce the marking.

Again, although matte in appearance, this glaze has a high melt fluidity. That means that brush-on colors could bleed. However if you keep it thin enough this should not be an issue. If it is consider using the G2934 original recipe.

1100 water, 1000 powder to get creamy mix.
Regular 2934 (with dolomite) took more water, about 1300. Nicer surface than G2934, same matteness, better fluidity.

An incredible silky matte surface supports wild colors at cone 6 oxidation

An incredible silky matte surface supports wild colors at cone 6 oxidation

This is the G2934Y matte base recipe with only 8% Cerdec Orange encapsulated stain. G2934Y employs a frit-source for the MgO (as opposed to G2934 which sources the MgO from dolomite). The orange color is brighter on the mug on the left because the porcelain is whiter, Plainsman Polar Ice (the other one is #6 Tile Kaolin based, P300). If this was a glossy glaze the required percentage of stain would be higher. Other colors, like yellow, are equally vibrant. But not all, testing is needed.

G2934 vs. G2934Y cone 6 yellow mattes

G2934 vs. G2934Y cone 6 yellow mattes

They have the same chemistry, but Y, on the right, sources MgO from a frit rather than from dolomite. Y is has a more fluid melt so it is not as opaque against the black slip underneath (thus it looks better on translucent porcelains). However its surface is just slightly finer. The Y one appears darker on the porcelain tile but it is actually brighter. The Y version is more likely to fire to a functional matte because it employs a frit to source the MgO (instead of dolomite which is variable from region to region).

Matte glaze cutlery marks. Add 10% glossy glaze to it. No marking.

Matte glaze cutlery marks. Add 10% glossy glaze to it. No marking.

This is G2934Y (a version of the G2934 cone 6 matte base recipe that supplies much of the MgO from a frit instead of dolomite). Like the original, it has a beautiful fine silky matte surface and feels like it would not cutlery mark. But, as you can see on the left, it does! The marks can be cleaned off easily. But still, this is not ideal. The degree of matteness that a glaze has is a product of its chemistry. But can we fix this without doing any chemistry? Yes. By blending this with G2926B clear glossy (90:10 proportions) the marks are gone and the surface is only slightly changed.

Matte cone 6 glazes have identical chemistry but one melts more. Why?

Matte cone 6 glazes have identical chemistry but one melts more. Why?

These are 10 gram balls that we melted on porcelain tiles at cone 4 (top two) and cone 6 (bottom two). They compare the melt fluidity of G2934 (left) and G2934Y (right). The Y version sources its MgO from frit and talc (rather than dolomite). It is a much more fluid melt because the frit is yielding the oxides more readily. But Y has a key benefit: It has a much lower LOI, producing fewer entrained air bubbles and therefore fewer surface defects. And, even though it runs much more, it has the same matte surface! As long as it is applied at normal thickness, the extra melt fluidity does not cause any running. And it has another benefit: Less cutlery marking issues. It is actually a very durable and practical food surface glaze, having a low thermal expansion that fits almost any body. Although these appear glossy here, on ware they have the identical pleasant silky matte surface.

Cobalt and iron overglazes bleeding into the matte glaze

Cobalt and iron overglazes bleeding into the matte glaze

This is the G2934Y matte base with overglaze decoration fired at cone 6. Although this matte has a high melt fluidity, overglaze decoration can be successful as long as it is not applied too thick and not overfired. But in this case the glaze is thickly applied. Once the critical thickness boundary is passed, the glaze's ability to hold overglaze in place quick degrades. The G2934 recipe has less melt fluidity and fires to the same surface, it would would be a better choice as the base glaze in this case (and could be applied thicker). However this Y variation would be a good choice as the medium if you want to make your own overglaze brushable colors.

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By Tony Hansen

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