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Cone 6 Stoneware/Whiteware Glossy Base Glaze

Code: G2916F
Modification Date: 2016-11-12 22:21:45
Member of Group: Cone 6

Crystal clear industrial dinnerware glaze

Fusion Frit F-52417.8
Old Hickory #5 Ball Clay7.7
Nepheline Syenite25.7


This is an industrial tableware glaze recommended by tech support at Fusion Frits. It not only fires hard and crystal clear but has outstanding suspension and application properties. You may think that you already have a good transparent cone 6 glaze, but try comparing it side-by-side with this (especially on a porcelain piece).

The magic for the way this glaze fires and its hardness and durability lie in the variety of fluxes in contains and the very low boron content coupled with high SiO2 and Al2O3. The fluxes most likely to create micro-bubbles at this temperature are sourced in a frit. It has the traditional CaO and KNaO, but the talc adds MgO and the frit adds SrO plus a tiny bit of BaO. This mixed-oxide effect produces a very well melting glaze yet having excellent body (considering it has only 18% of a low-boron frit). makes this recipe as a premixed powder. But they will also have a stock of the frit if you want to make your own. The glazes section of thier site has additional guidelines on this use of this recipe.

Cautions In Mixing Your Own Glaze

-Screening is required during preparation if your wollastonite has agglomerated (otherwise your slurry will be full of tiny lumps).

-Fusion recommends 325 mesh silica and A400 nepheline syenite, but we have been using regular 200 silica and 270 nepheline with good success for stoneware.

-The recipe originally used #1 Glaze Ball Clay, but we have switched to a very similar more commonly available product, Old Hickory #5 (it has the same kaolin-like nature of #1 Glaze). These two ball clays are dramatically better than others for suspending glazes, mix this with another and you may get a poor working-properties preview of this otherwise very good recipe. In addition, these ball clays are higher in Al2O3 than typical (29% vs 25%), so there is a slight chemistry impact in using another.

-Use your own bentonite if you cannot get the Milwhite Bentonite B. Milwhite is low in iron, use the cleanest bentonite you have.

To prepare it for use, add the powder to water and mix until it flows well. Screen through 80 mesh (there are tiny agglomerates that will not break down without screening). Adjust the amount of water to get a consistency such that on extraction from a 1-2 second dip the glaze hangs on in an even layer without dripping and dries in less than 10 seconds. The slurry needs to be slightly gelled to achieve this, so don't use too much water. Adjust your bisque temperature to get more porosity (if the glaze dries to slow) or less (if it dries too fast).



Cone 6 porcelain marbled and thrown

These bowls were made by Tony Hansen using a mixture of white and stained New-Zealand-kaolin-based porcelain (Plainsman Polar Ice) fired at cone 6. The body is not only white, but very translucent.

This glaze can dry on metal without cracking, even though it is thick!

This sample of glaze was dried under a heat lamp to measure its water content. If a glaze that is this thick can crack this little during drying and adhere even to stainless steel there is absolutely no reason you need to suffer glazes cracking during drying on bisque ware. This one is very high in frit with about 15% No. 5 ball clay. Drying cracking problems can be fixed using Digitalfire Insight, it enables you to juggle a recipe to reduce and substitute plastic ingredients while maintaining the chemistry.

Two stains. 4 colors. Will the guilty oxide please step forward.

We are looking at two pairs of samples, they demonstrate why knowing about glaze chemistry can be so important. Both pairs are the same glazes: G2934 cone 6 matte and G2916F cone 6 glossy. The left pair has 5% maroon stain added, the right pair 5% purple stain. The red and purple develop correctly in the glossy but not the matte. Why? The Mason Colorworks reference guide has the same precaution for both stains: the host glaze must be zincless and have 6.7-8.4% CaO (this is a little unclear, it is actually expressing a minimum, the more the CaO the better). The left-most samples of each pair here have 11% CaO, the right-most have 9%. So there is enough CaO. The problem is MgO (it is the mechanism of the matteness in the left two), it impedes the development of both colors. When you talk to tech support at any stain company, as I did with Mason on this, they need to know the chemistry of your glaze to help, not the recipe.

Mason stains in a cone 6 clear base

These are Mason stains added to cone 6 G2916F clear liner base glaze. Notice that all of these stains develop the correct colors with this base (except for manganese alumina pink 6020). However caution is required with inclusion stains (like #6021), if they are rated to cone 8 they may already begin bubbling at cone 6 is some host glazes.

M340 Transparent Liner with Mason stains

M340 Transparent Liner glaze fired at slightly lower than cone 6. Using these modest stain amounts the degree of melting of the glaze is not overly affected (these were balls, they flattened during firing). However as a glaze layer on a body, many of these will not be as dark as you see here.

Mason stains in a cone 6 clear base

These are Mason stains added to cone 6 G2926B clear liner base glaze. Notice that the chrome tin maroon 6006 does not develop as well as the G2916F glossy base recipe. The 6020 manganese alumina pink is also not developing. Caution is required with inclusion stains (like #6021), if they are rated to cone 8 they may already begin bubbling at cone 6 is some host glazes.

Stains having varying fluxing effects on a host glaze

Plainsman M340 Transparent liner with various stains added (cone 6). These bubbles were fired on a bed of alumina powder, so they flattened more freely according to melt flow. You can see which stains flux the glaze more by which bubbles have flattened more. The deep blue and browns have flowed the most, the manganese alumina pink the least. This knowledge could be applied when mixing these glazes, compensating the degree of melt of the host accordingly.

Tune your matte glaze to the degree of matteness you want

G2934 is a popular matte for cone 6 (far left). It is not matte because it is not melting enough or is covered with micro-crystals, it is an MgO matte (a mechanism produces a more pleasant surface that cutlery marks and stains less). But what if it is too matte for you? This recipe requires accurate firings, did your kiln really go to cone 6? Proven by a firing cone? If it did, then we need plan B: Add some glossy to shine it up a bit. I fired these ten-gram balls of glaze to cone 6 on porcelain tiles, they melted down into nice buttons that display the surface well. Top row proceeding right: 10%, 20%, 30%, 40% G2926B added (100% far right). Bottom: G2916F in the same proportions. The effects are similar but the top one produces a more pebbly surface.

At what temperature do cone 6 glazes seal off the surface of the body?

These are 10 gram balls of four different common cone 6 clear glazes. I fired them to 1800F (bisque temperature) to see how dense they would be. Why? To answer this question: If the gases of decomposing lignite have not been fully expelled from the clay body during bisque, then could a glaze densify enough to seal the surface from that temperature up? The answer appear to be yes. I measured the porosity of these (weighing, soaking, weighing again): G2934 - 21%. G2926B - 0%. G2916F - 8%. G1215U - 2%. The implications: Glaze pinholes in improperly bisqued ware.

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By Tony Hansen

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