How much light magnesium carbonate supplies the same MgO as 50 parts magnesium oxide? An Insight-live account enables calculating it. These two test recipes show how. Each contains the same 50 parts Ferro Frit 3134. In calculation mode, increase the magnesium carbonate in steps of 10 until the calculated oxide formulas match. But notice the recipe totals: 100 versus 170. Much of that extra weight escapes during firing as carbon dioxide and water vapor. The carbonate recipe has a calculated loss on ignition (LOI) of 40.2%, compared with zero for the oxide version.
However, the similar calculated chemistry does not guarantee similar firing behavior. At this exceptionally high proportion, light magnesium carbonate strongly promotes crawling: Its fine particles increase drying shrinkage, and its effect on the melt helps the glaze pull into islands. The high LOI adds a substantial gas burden. Glaze chemistry tells us what oxides materials supply, but their physical properties and decomposition behavior matter too.

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You will see examples of replacing unavailable materials (especially frits), fixing various issues (e.g. running, crazing, settling), making them melt more, adjusting matteness, etc. Insight-Live has an extensive help system (the round blue icon on the left) that also deals with fixing real-world problems and understanding glazes and clay bodies.
| Materials |
Magnesium Oxide
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| Materials |
Light Magnesium Carbonate
A refractory feather-light white powder used as a source of MgO and matting agent in ceramic glazes |
| Temperatures | Decarbonation (200-1000) |
| Typecodes |
Glaze Chemistry
Case studies where glaze chemistry was used to solve a problem. |
| Glossary |
LOI
Loss on Ignition is a number that appears on data sheets test results of ceramic materials and bodies. It refers to the amount of weight lost as it decomposes to release water vapor and various gases during firing. |
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