Dolomite is a calcium magnesium carbonate, which means one bag supplies two of the most useful fluxes in stoneware glazes at once. It is the material behind a great many of the smooth satin and silky matt surfaces on functional studio pottery.
Two fluxes in one material
Calcium is the standard high-temperature flux and magnesium gives the buttery matt quality described elsewhere on this site. Dolomite delivers both in a fixed ratio, which makes it convenient and slightly less flexible than adding whiting and a magnesium source separately. For most recipes the convenience wins.
The dolomite matt
A classic dolomite matt is smooth rather than dry, pleasant to touch, and opaque enough to hide the body without being chalky. It is a mainstay of tableware because it wears well and feels good in the hand, and because the magnesium in it moves colourants into softer, less strident ranges.
Where it goes wrong
Too much dolomite gives a dry, underfired-looking surface that can be difficult to clean in use, and magnesium matts can be susceptible to marking from cutlery on flatware. Both are matters of percentage and firing, and both are found on a test tile long before they are found on a dinner service.
Buying and handling
Dolomite is inexpensive and sold by the bag as a fine powder. It carries the same weighing precautions as everything else on this shelf: ventilation, a fitted respirator and wet cleaning rather than sweeping. Kept dry it lasts indefinitely.
Questions people ask about dolomite powder
What does dolomite do in a glaze?
It supplies calcium and magnesium together, fluxing the glaze and giving the smooth silky matt surfaces common on functional pottery.
Is a dolomite matt good for tableware?
It is widely used for it and wears well. Test for cutlery marking on flatware, which magnesium matts can be prone to.
Can I use whiting instead?
Whiting supplies calcium only. You would need a separate magnesium source to reproduce a dolomite glaze.