Mogusa Clay is a clay from Mino (modern day Gifu). Named after the loose fiber used for moxibustion, the clay is special for its coarse, sandy texture. When trimmed, it organically splits and tears.
I have not worked with Japanese Mogusa clay, so these properties are deduced from pictures and videos.
Since the tearing properties of Mogusa are purely physical, it can be possible to alter the color and maturity at will by carefully selecting the clay and feldspar portion. Then the issue becomes the filler: how much of it and what kind?
Silt is non-plastic with particles finer than sand but coarser than clay. For reference, clay particles are 2 microns and finer. There are several definitions of silt particle size:
This test compares a typical white stoneware body and the same body with 10% added 50-80 mesh molochite grog. ... Notice another issue: The jagged edges of the disk, it is more difficult to cut a clean line in the plastic clay.
From Digital Fire: Do grog additions always produce better drying performance?
Notice the edges have peeled badly during cutting, this is characteristic of very low plasticity clays.
From Digital Fire: [Albany Slip DFAC dried disk](https://digitalfire.com/picture/jywpowetim
[Splitting] can happen during tooling. While the plasticity is sufficient for throwing, at lower water contents it drops off quickly. This is a mix of 5% bentonite, 10% ball clay and 85% calcined alumina. For better trimming some refractory capability needs to be sacrificed for more ball clay (perhaps 20%).
From Digital Fire: A body containing excessive non-plastics having a high bentonite addition for plasticity
When formulating a porcelain that employs a white expensive plasticizer the optimal range of prcentages can be surprisingly narrow. The trimming behavior is one indicator. When there is insufficient plasticizer the tool will chatter (of course in extreme cases edges will tear). Smoothing the corners after trimming (using your finger) will aslo give you an indication. If there is too much plasticizer, the material will ball up under your finger, if there is insufficient it will not smooth out well.
From Digital Fire: How much VeeGum is needed in a super white porcelain?
From the above snippets, I would make a Mogusa clay by
The clay is trimmed while still relatively soft with a dull (wooden) knife.
If the clay is too dry, it won't tear and create texture.
| Material | Percentage |
|---|---|
| Helmer Kaolin | 30 |
| Optikast Kaolin | 20 |
| Nepheline Syenite | 30 |
| Silica 200 Mesh | 10 |
| Kyanite Grog 48 Mesh | 10 |
| Bentonite | +2 |
This clay successfully tears but trimming it is difficult. The clay has a very narrow window between workable and too stiff. When too stiff, the clay comes off in large chunks and it's very easy to tear the foot ring completely off.
The clay needs to be more plastic.
| Material | Percentage |
|---|---|
| Helmer Kaolin | 20 |
| Tennessee 10 Ball Clay | 30 |
| Nepheline Syenite | 20 |
| Silica 325 Mesh | 20 |
| Mulcoa Grog 47-48 | 10 |
TODO: add picture of teacup
| Material | Percentage |
|---|---|
| Tennessee 10 Ball Clay | 30 |
| Silica 325 Mesh | 30 |
| Pyrophyllite | 20 |
| Mahavir Feldspar | 20 |
I think the grog is unnecessary. It's possible to get the tearing texture just from the grainier ingredients in the clay. This is the silty content: silica and pyrophyllite grains facilitate the tearing.
Same tearing texture can be found in
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