Increasing demands for additional output and longer life from container glass furnaces are generating interest in improving melting and fining rates. This has resulted in widespread use of electric boosting, deeper tanks, and fining agents. Over the years, glassmakers have made a general observation that reduced glasses are easier to fine than oxidized ones. Carbon-sulfur amber glasses have extremely short fining times while ultraviolet absorbing green glasses, which are highly oxidized, are very difficult to fine. Historically, flat glass producers use carbon in conjunction with saltcake, principally to control the amount of salt water. However, many now think that carbon acts as a reducing agent to promote fining. More recently, within the last 6 years, some container glass manufacturers have been adding small amounts of carbon to the batch. Conflicting results are reported, but the majority claim a substantial reduction in seeds. Interest has grown in other reducing agents such as sulfur and sulfides as fining agents. This study was made principally to determine the fining effect of sulfides, sulfur, and sulfite. Sodium hydrosulfide was chosen because it is stable in caustic soda, does not contain metals which colour the glass, is readily available, and is convenient to introduce.
