Carbonates
Carbonates are chemical compounds containing the carbonate ion (CO₃²-) as the main component. In ceramics, they are essential materials that play key roles in the formulation of clays, engobes and glazes. These compounds decompose during firing at high temperatures, releasing carbon dioxide (CO₂) and leaving metal oxides that react with other components, modifying both the physical and aesthetic properties of ceramic pieces.
Among the most commonly used carbonates in ceramics is calcium carbonate (CaCO₃), which acts as a flux and stabilizer in glazes, helping to reduce the melting point and improving the cohesion of the material. Sodium carbonate (Na₂CO₃), known as soda, is used in the creation of glossy and translucent glazes, while potassium carbonate (K₂CO₃) or potash has similar applications, intensifying colors and favoring vitrification. Also notable are manganese carbonate (MnCO₃), used as a colorant to obtain brown, purple and black shades, as well as copper carbonate (CuCO₃), which produces green and turquoise tones, and cobalt carbonate (CoCO₃), famous for its deep and stable blues.
In ceramic decoration, carbonates are prized for their ability to create vivid colors and unique visual effects, depending on how they interact with the kiln atmosphere (oxidation or reduction), firing temperature and the other components of the ceramic mixture. For example, copper carbonate is known to produce a vibrant green on oxidation and a deep red on reduction, making it a very versatile material in the creation of reactive glazes.Interesting Fact
Carbonates have been used since ancient times in ceramics. For example, the Egyptians and Romans used copper carbonate to decorate their vessels, while in Asia, cobalt carbonate was a key material in the creation of blue and white porcelains, a tradition that is still highly valued.Helpful Tip
When working with carbonates, be sure to sieve the materials well before incorporating them into mixtures, as this ensures even distribution and avoids defects in the glaze surface. Some carbonates, such as copper or manganese, can be toxic in powder form, so it is important to wear gloves, mask and work in a ventilated area.