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Matte Glaze Base for Cone 6

Code: G2934
Modification Date: 2018-08-13 12:07:21

A base MgO matte glaze recipe fires to a hard utilitarian surface and has very good working properties. Blend in the glossy if it is too matte.

MaterialAmount
Ferro Frit 312417.4
Dolomite23.5
Silica26.9
EP Kaolin18.3
Calcined Kaolin13.9
 100.00  

Firing Schedule

Rate ()Temp ()Hold (Min)Step
108250601
350209502
1082195103
9992095304

Notes

A cone 6 boron-fluxed MgO matte developed at Plainsman Clays by Tony Hansen (a link below will take you to its page there). This page contains technical and mixing information about the recipe.

In its current state it does not cutlery mark and has good (but not too much melt flow) and thus creates a good glass (in our circumstances). The development process for this glaze showcases the value of looking at glazes as formulas of oxides rather than recipes of materials.

The calcined kaolin is needed to supply the Al2O3 but not increase the drying shrinkage (if you do not have calcined kaolin you can make your own by bisque firing a container of kaolin powder).

Notice also, that although a matte, this recipe has a high silica content. However, the matteness mechanism is somewhat fragile (it will be more matte for some people, more glossy for others; due to material (especially with local dolomites), process and firing differences). In addition, certain colors will matte it more and others will gloss it more. For most people a simple addition of G2926B (M370 transparent ultra clear base recipe) will increase the gloss. Start by adding 10% and testing (since this and the gloss mix to about the same specific gravity, just measuring by volume of slurry is a fairly accurate way to judge the percent addition). Be prepared to adjust each color variation to fine tune its degree of gloss.

In our circumstances, this recipe has very good suspension and application properties. It dries hard, does not crack during drying, does not settle hard in the bucket and applies evenly and dries quickly. If you do not have EP Kaolin, just substitute. That may require adjusting the raw:calcine proportions. If it settles convert some of the calcined kaolin to raw. If it does not dry hard enough or does not suspend well, use more raw kaolin and less calcined. However because the raw kaolin has 12% weight loss on firing, more is needed to supply the same amount of SiO2 and Al2O3 to the fired glaze. For example, if you drop the calcined kaolin by 5 you need to increase the raw kaolin by 5.6 to maintain the same overall chemistry (5 + (5 x 12% / 100 = 5.6). If your kaolin is not too plastic you might be able to use all raw kaolin (18.3 + 13.9 + (13.9 x 12% / 100) = 34. But beware, the glaze could crack on drying (and thus crawl on firing).

To prepare it for use, target a specific gravity of 1.43-1.44. Divide the total weight of powder by 1.1 to derive the amount of water to use. This should produce a specific gravity slightly higher so that you can add water and fine tune it down. If it is not creamy add a flocculant (see the thixotropy glossary entry link below for more information on doing this).

Screen through 80 mesh (there are tiny agglomerates that will not break down without screening).

Although this is a matte glaze it flows well (it is well melted). If fired ware has pinholes the solution lies elsewhere. Bisque ware as high as possible. If you gel the slurry a little, or preheat the ware, you can bisque even higher. Try applying a thinner glaze layer and use whatever technique necessary to get an even and quality laydown. If still needed, consider using the double-soak firing schedule.

Plainsmanclays.com makes this recipe as a premixed powder.

Important note: This glaze is firing to a surface that some people find too dry. One reason for this is variation in different brands of dolomite. To help with this issue we have created an chemistry-equivalent that sources the MgO from a frit and talc, G2934Y (see link below). It also has a better melt fluidity (and thus is a little less opaque and hosts stains better), a much lower LOI and the surface is just slightly more silky.

Out Bound Links

In Bound Links

XML to Paste Into Insight

<?xml version="1.0"?>
<recipes version="1.0" encoding="UTF-8">
<recipe name="Matte Glaze Base for Cone 6" keywords="A base MgO matte glaze recipe fires to a hard utilitarian surface and has very good working properties. Blend in the glossy if it is too matte." id="121" date="2018-08-13" codenum="G2934">
<recipelines>
<recipeline material="Ferro Frit 3124" amount="17.400" unitabbr="kg" conversion="1.0000" added="0"/>
<recipeline material="Dolomite" amount="23.500" unitabbr="kg" conversion="1.0000" added="0"/>
<recipeline material="Silica" amount="26.900" unitabbr="kg" conversion="1.0000" added="0"/>
<recipeline material="EP Kaolin" amount="18.300" unitabbr="kg" conversion="1.0000" added="0"/>
<recipeline material="Calcined Kaolin" amount="13.900" unitabbr="kg" conversion="1.0000" added="0"/>
<url url="https://digitalfire.com/4sight/recipes/matte_glaze_base_for_cone_6_121.html" descrip="Recipe page at digitalfire.com"/>
</recipelines>
<urls/>
</recipe>
</recipes>


By Tony Hansen




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