A chemical with the formula Na₂CO₃. It is called soda ash at the drilling rig and is used to treat most types of calcium ion contamination in freshwater and seawater muds. For cement contamination, sodium bicarbonate is used. Calcium ions from drilling gypsum or anhydrite, CaSO₄, cause clay flocculation and polymer precipitation and lower pH. A soda-ash treatment is appropriate for gypsum contamination because caustic soda, NaOH, is not needed to raise pH. This is also generally the case with hard water influxes into water muds.