Mulcoa is a Grog that is chemically 47% alumina and has coarse particles between the sizes of 20 and 50 mesh.
| Quantity | Notes |
|---|---|
| 3% | Gives better structure to less plastic clays. Very visible pits and scratching during trimming. |
| 10% | Rather rough. Clay must be on the softer side for throwing. Trimming is difficult as tools scrape and jump on grog particles. |
Mulcoa 47-20x50 is a great addition to clay bodies for throwing large vases. 3% grog in a plastic clay is not too rough when throwing, but makes lifting somewhat easier. 10% grog is a little rough on the hands, but makes it possible to throw tall cylinders that would be otherwise impossible. The grog interlocks with itself, preventing folding and twisting when throwing.
Trimming clay with Mulcoa 47-20x50 can be rough on the trimming tools, especially when the clay is harder. Clay is best trimmed when on the softer side of leather. Trimming also leaves holes and lines where the grog is gouged out or dragged along the surface of the clay. Since I only trim near the bottom of my pots, I prefer to leave this texture, but it can be smoothed over with some wet clay or slip.
When the clay dries and is fired, it shrinks away and exposes the grog. Since the grog is coarse, any amount will leave texture on the surface of the clay even if burnished. 10% produces a highly tactile surface.
, which only contains 3% Mulcoa 47-20x50. There are many pits and scratches (where the trimming tool dragged grog across the clay surface). Where the bowl is untrimmed, the texture of the grog still shows through and is pleasantly tactile.
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