The two key characteristics of Calumite that contribute to the range of benefits that it offers are its glassy nature and its redox value.
The glassy nature of Calumite means that it works a lot like cullet (recycled glass), providing a range of glassmaking oxides to the melt, already in a glassy form so that less energy is required to melt a Calumite containing batch. For example, Calumite provides between 15 and 40% of the CaO in the new glass from batch, reducing the amount of limestone and dolomite required. This reduces the energy required for the endothermic decomposition of limestone and dolomite that occurs around 800-900°C. Calumite is glassy and liquid at glass melting temperatures, and therefore available to take part in batch reactions at lower temperatures.
Calumite is a reducing agent due to the presence of small amounts of carbon and sulphur as sulphide. Due to the low levels of sulphide, it is a weak reducing agent when compared to others that might be used. As a result, comparatively large amounts of Calumite are added to the recipe, resulting in more even distribution within the batch. The interaction of Calumite with sodium sulphate reduces the temperature at which sodium sulphate decomposes, giving the beneficial effects of sodium sulphate refining at lower temperatures.