Secondary or residual clays
Secondary clays, also known as residual clays, are those that have been transported from their place of origin by natural erosion processes, such as water, wind or ice. Throughout this transport process, clay particles are mixed with various materials and minerals that may include metals, carbonates, organic matter and other compounds, resulting in a more complex composition compared to primary clays. Impurities that are incorporated during transport, such as oxides and carbonates, are responsible for a variety of colors in secondary clays, ranging from reddish and brownish tones to darker colors.
One of the main advantages of secondary clays is their greater plasticity. The presence of impurities, such as carbonates and organic matter, increases the clay's ability to absorb water and become more malleable and easier to work. This increased plasticity makes them a preferred choice for hand modeling and wheel working techniques, where more flexible and workable clays are required. However, this same characteristic can make secondary clays more susceptible to deformation during drying and firing, as their higher water content and other compounds can affect the stability of the pieces.
Due to the impurities present, secondary clays have a more variable firing point compared to primary clays. Firing temperatures can fluctuate depending on the type and amount of impurities, which means that the firing process must be fine-tuned to avoid deformation or cracking of the pieces.Interesting Fact
Secondary clays can be more economical than primary clays because of their greater availability and less processing. Because these clays tend to be found in larger deposits and are often easier to extract, their cost tends to be lower.Helpful Tip
To improve the plasticity of a low-quality clay, mix a secondary clay with a purer primary clay and experiment with different proportions until you find the ideal combination for your project.
