Matte glazes have a bad reputation for cutlery marking, and the reputation is deserved for the ones built on excess alumina or on under-firing. A magnesium matte is different: the surface is a fully melted glaze that grows tiny crystals as it cools, so it is durable and still reads matte. This is the recipe, the cooling it needs, and the test that tells you whether it will mark.
H 12 · Ø13 / Ø14 / Ø7.5 cm
Base
A cone 6 matte built on magnesium rather than on excess alumina. Talc and dolomite supply the magnesium; the satin comes from small crystals forming at the surface during cooling, not from under-firing.
| Material | Parts | Share |
|---|---|---|
| Custer Feldspar | 28 | 28.0% |
| Silica (SiO₂) | 22 | 22.0% |
| Talc | 20 | 20.0% |
| EPK Kaolin | 18 | 18.0% |
| Dolomite | 12 | 12.0% |
| Total charge | 100 |
Fired surface
A hard satin that reads matte in daylight and shows a faint sheen at a low angle. Breaks warm amber over iron-bearing bodies and stays flat and even over white.
Two ways to make a matte, only one of which is durable
The first way is to under-fire a glossy glaze so that it never fully smooths out. It looks matte and it scratches with a fork, because the surface is a partially melted network rather than a glass. The second way is to melt the glaze completely and then encourage magnesium crystals to form on the surface during cooling, which produces a hard, chemically stable surface.
The dead giveaway is the fired surface under a loupe: an under-fired matte looks like a landscape with visible grain and pinholes; a crystallised matte looks like a smooth surface with a faint, uniform haze. If your matte looks like the first one, you are under-firing and no amount of hardness testing will help.
Where the magnesium comes from
Talc supplies magnesium and silica together, which is why it is the traditional matte material — adding talc raises the magnesium without dropping the silica the way dolomite does. Dolomite supplies magnesium and calcium together and is a stronger flux than talc, so at 12 percent here it does the melting work while the talc does the crystallising.
Above 25 percent talc the glaze stops melting properly at cone 6 and turns dry and powdery. Below 12 percent it goes glossy. The window is narrow, which is why this is a recipe to adjust in 2 percent steps rather than 5.
The cooling it needs
A magnesium satin needs a slightly slower cool than a glossy glaze to develop its surface. Drop from cone 6 to 1000 degrees at 100 degrees per hour rather than letting the kiln fall naturally, which for most electric kilns means holding the damper shut and not opening the lid.
The difference is visible. The same glaze on the same clay, cooled naturally in five hours, comes out glossier and slightly more transparent; cooled over eight hours it is unmistakably satin. If you fire mixed loads, put the matte pieces on the shelf that cools slowest — normally the middle.
The cutlery test
Fire three plates in this glaze, then drag the back of a stainless steel fork across the surface ten times with moderate pressure. A durable matte leaves a faint grey line that wipes off with a damp cloth; a soft matte leaves a permanent dark scratch.
If it scratches, do not add more silica — that makes it glossier, not harder. The fix is a slightly higher top temperature or a longer soak, which completes the melt. Two minutes more at cone 6 will convert a scratching matte into a durable one without changing its appearance.
Steps
- Weigh the five materials and combine them dry.
- Add water to 1.42 specific gravity, which is slightly thinner than a glossy glaze.
- Sieve through 80 mesh and add 0.15 percent Epsom salts if it settles hard.
- Dip test tiles for one second, targeting a 0.35 mm deposit — mattes break badly above 0.5 mm.
- Fire to cone 6 with a 10 minute soak at the end.
- Cool from cone 6 to 1000 degrees at 100 degrees per hour rather than naturally.
- Drag a stainless fork across a fired test plate ten times and check for a permanent scratch.
- Raise the soak to 15 minutes if the surface scratches, rather than changing the recipe.
Where it goes wrong
- Adjusting the recipe to fix scratching. Scratching is almost always an incomplete melt, not a materials problem.
- Applying at 0.6 mm. Mattes break to glossy at every edge when they are thick.
- Letting the kiln cool naturally. You lose about half the satin quality.
- Using talc that has been sitting open in the studio for years — it absorbs moisture and throws the recipe's water demand off.
| Symptom | Cause |
|---|---|
| Cutlery leaves a permanent dark scratch | the glaze was under-fired; extend the soak rather than changing the recipe. |
| Glaze went glossy instead of satin | cooled too fast, or the talc was below 12 percent. |
| Dry, powdery surface with visible grain | talc above 25 percent, so the glaze never fully melted. |
| Colour breaks to bright gloss at every rim | applied above 0.5 mm; thin the glaze to a 0.35 mm deposit. |
Recipe and schedule numbers here were recorded on the workshop’s own kiln. A different kiln, a different thermocouple position or a different clay batch will move the result, so treat every firing schedule as a starting point and keep your own log beside it.
Same cone — Cone 6
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