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Five common North American Ferro Frits fired at 1850F on alumina tiles (each started as a 10-gram GBMF test ball and flattened during the firing). At this temperature, the differences are more evident than at 1950F. The degree of melting corresponds mainly, but not only, to the percentage of B2O3 present. Frit 3134 is the runaway leader because it couples that with almost no Al2O3 to stabilize the melt. Notice also the crack pattern, it is also very high in Na2O and thus has a high COE. However, why does Frit 3110 melt so well even though it contains almost no B2O3? Even higher Na2O, it is a powerful flux. Its COE is even higher than Frit 3134, but it is thick enough to have resisted cracking far (but it will in time).

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I used Veegum to form 10 gram GBMF test balls and fired them at cone 08 (1700F). Frits melt really well, they do have an LOI like raw materials. These contain boron (B2O3), it is a low expansion super-melter that raw materials don’t have. Frit 3124 (glossy) and 3195 (silky matte) are balanced-chemistry bases (just add 10-15% kaolin for a cone 04 glaze, or more silica+kaolin to go higher). Consider Frit 3110 a man-made low-Al2O3 super feldspar. Its high-sodium makes it high thermal expansion. It works really well in bodies and is great to make glazes that craze. The high-MgO Frit 3249 (made for the abrasives industry) has a very-low expansion, it is great for fixing crazing glazes. Frit 3134 is similar to 3124 but without Al2O3. Use it where the glaze does not need more Al2O3 (e.g. already has enough clay). It is no accident that these are used by potters in North America, they complement each other well (equivalents are made around the world by others). The Gerstley Borate is a natural source of boron (with issues frits do not have).
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Ferro Frit 3124
A commonly available calcium borosilicate frit. |
| Materials |
Ferro Frit 3134
A frit with 23% B2O3. The most common of frits used in pottery in North America. Around the world, other companies make frits of equivalent chemistry. |
| Materials |
Ferro Frit 3195
A commonly used boron frit, it is a balanced glaze all along at cone 06-02 (with the addition of 10-15% kaolin). Not fully glossy. |
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Ferro Frit 3110
High sodium, high thermal expansion low boron frit. A super-feldspar in clay bodies. Melts a very low temperatures. |
| Materials |
Ferro Frit 3249
A magnesia borosilicate frit. Very low thermal expansion and melting point. Invaluable in pottery to increase the MgO in glazes and thereby prevent crazing. |
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