• In ceramics, a flux additive will lower the melting point of materials. Fluxes are introduced to the raw glaze and can be composed of a variety of different base materials such as wood ashes, sodium, potassium, lithium, boron, calcium, magnesium, lead, zinc, iron, and others. 1


  • Flux additives consist of naturally occurring chemical compounds, many of which are minerals and metals that are found all over the world or produced synthetically. For example, dolomite, which is a common flux additive, has a chemical makeup of calcium, magnesium, and carbon, it is mined throughout Europe, Canada and Africa. 2,3


  • It may take centuries for glazed ceramics to biodegrade; however, ceramic is less harmful to the environment than materials like plastic. 5
  • Mining the minerals and metals for flux additives requires a lot of energy and causes damage to wildlife and water systems. In addition, firing also takes up large amounts of energy and leaching of heavy metals can occur when ceramic products are glazed incorrectly or damaged.4

Human Health

  • Flux additives, more often than not, are highly toxic and can leach out of glazes, even after firing.  Nepheline syenite and barium carbonate fluxes are commonly used; these are both slightly hazardous and may cause irritation due to overexposure in the studio. 2,7,8 Lead based fluxes are not used at Pratt.

Safe Use and Exposure

  • The most common base ingredients of flux additives are toxic by inhalation, ingestion, or skin contact;  Lead-based fluxes are particularly dangerous to work with due to the possibility of lead poisoning. When working with flux wear a facemask and gloves.2, 4

Proper disposal

  • Unwanted toxic glazes should be fired and then disposed of in a hazardous material bin or the regular trash, depending on the toxicity of the flux additive within the glaze. Leftover nontoxic glazes can be collected in a slop bucket and then reused. 9 Donate any usable glaze to the givetake.

Safe Alternatives

  • Take caution when choosing glazes. Be sure the label states “lead-free.” If there is no information, assume the glaze contains a lead-based flux additive, until proven otherwise. Non-toxic glazes are marked with the AP seal 4


  1. “Ceramic and Glaze Fluxes”,,
  2. “Glossary of Ceramic Raw Materials”, Lakeside Pottery,
  3. “Dolomite Facts”,,
  4. “Ceramics”, Princeton University EHS,
  5. “How Eco Friendly is Ceramic?”, Eluxe Magazine,
  6. “Ceramic Glaze”, Wikipedia,
  7. Laguna Clay Nepheline Syenite MSDS,
  8. “Barium”, ASTDR,
  9. “Cone 6 Glaze Creations”, Big Ceramic Store,