Barium carbonate produces some of the most distinctive matt surfaces in ceramics: dry, silky and often intensely coloured, quite unlike a matt produced by underfiring. It is also one of the materials on this shelf that carries genuine handling requirements rather than routine ones.
What it does in a glaze
Barium acts as a flux at high temperatures and, at higher percentages, produces a distinctive dry matt surface with a silky feel. Colourants in a barium matt often read stronger and more saturated than in a glossy base, which is why the barium blues and greens of the 1970s studio tradition look the way they do. It is a specific effect that no other material reproduces exactly.
In a clay body
A small addition of barium carbonate to a body precipitates soluble salts and prevents scumming, the whitish bloom that appears on some fired earthenware. That is an industrial use that occasionally appears in studio recipes, and it involves far smaller quantities than a glaze application.
Handling, and why it is singled out
Barium carbonate is toxic if ingested, and the practical precautions are a fitted respirator when weighing, gloves, ventilation, wet cleaning and keeping it away from anywhere food is prepared. Those are stricter than for iron or silica and are worth stating rather than assuming: it sits on a price list beside gentler materials with nothing about its position to signal the difference.
Substitutes and the food question
Strontium carbonate gives a similar matt with a better-regarded safety profile and is the usual substitute, though the surfaces are not identical. For anything that will hold food, this site quotes the manufacturer's data sheet for a specific glaze and firing and asserts nothing itself, and a barium matt is exactly the kind of glaze where that distinction matters.
Questions people ask about barium carbonate
What does barium carbonate do in a glaze?
It fluxes at high temperature and, at higher percentages, gives a distinctive dry silky matt with strongly saturated colours.
Is barium carbonate safe to use?
It is toxic if ingested and needs a fitted respirator, gloves, ventilation and wet cleaning. Keep it away from food preparation areas.
What can I use instead?
Strontium carbonate gives a similar matt and is the usual substitute, though the surfaces are not identical.