Impurities may also manifest as electron spin impurities in certain materials. Carbon filtering removes remaining contaminants and impurities by chemical absorption onto activated carbon. Ash is formed in gasification from inorganic impurities in the coal. Moringa seed cake removes most impurities from water. This causes the dissolved impurities (such as silicon) to be thoroughly oxidized. It is as free from ash, sulfur, and other impurities as possible. Early glass was rarely transparent and often contained impurities and imperfections. The slag is a liquid mixture of ash, flux, and other impurities. Type II diamonds have no measurable nitrogen impurities. The yellow color is caused by nitrogen impurities. Deodorization of DMSO is achieved by removing the odorous impurities it contains. High-quality salt with little mineral impurities is preferred. Type II diamonds have very few if any nitrogen impurities. Even small quantities of such impurities can cause such effect. The bulk modulus is affected by temperature, pressure, and dissolved impurities (usually salinity).