Using additives for color control in copper-containing glasses

When added to glass-forming melts, copper establishes the Cu2+-Cu+ redox equilibrium under oxidizing conditions, and the Cu+-Cu-0 equilibrium at reducing conditions. Cu2+ typically introduces a blue coloration to glass, while Cu-0 imparts a ruby red color (Cu+ is colorless). A systematic study investigated the ability of additives (iron; and cerium, chromium, europium, manganese, nickel, lead, uranium, and vanadium, individually or in concert with iron) to undergo redox reactions with copper during the processing of an alkali borosilicate glass. Such interactions were determined in glass melts with Cu2+, Cu+, or Cu-0 as copper's predominant redox state and were monitored by spectral changes. Depending on the synthesis conditions, a particular additive could be a reducing agent, oxidizing agent, or redox neutral with respect to the prevailing copper redox states. The results illustrate that an electromotive force series of redox couples can be used to predict the effect of an additive on the copper redox state(s) in the glass.