Grog is powdered refractory ceramics added to clay. The sharp particles of grog interlock, improving throwing properties.
Clay with grog may seem deceptively short if you use the coil test. When you make a coil and bend it, the clay may tear because grog particles are large and not plastic. Yet when you throw, the grog increases strength and the clay will feel more plastic than a clay with no grog and similar tearing behavior.
| Material | Notes |
|---|---|
| Molochite | Very white calcined kaolin. Useful as porcelain grog. |
| Kyanite | |
| Mullite | Calcined kaolin. Mulcoa brand grog (Mulcoa Grog 47-20x50, Mulcoa Grog 47-35, Mulcoa Grog 47-48) is mullite. |
| Quartz (Sand) | Usually rounded, which creates a smoother texture. Visually reacts in Soda Firing |
Mesh size determines how abrasive the grog feels. Larger particles are rougher on the hands and smaller particles can be imperceptible.
| Mesh Size | Notes |
|---|---|
| 20 | Rather rough, but up to 10% is bearable in throwing bodies. Deep gouges when trimming. |
| 30 | You need to pay attention to feel it. Leaves pits and marks while trimming. |
| 40 | |
| 50 | Imperceptible while throwing. Can affect the texture of slips and untrimmed areas. Duller trimming tools may not leave any marks. |
For comparison, Hawthorne Bond is sold in 40 and 50 mesh sizes.
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