It is used together with some other colouring agents to intensify or change the colour. In this device the spectral transmission i.e. the amount of light passing through the glass in different wavelengths is measured. Typically the measurement is done at 5 nm intervals. However, if thinking of the visual appearance, only the range of the visible light is important. The problem with the X,Y,Z values is that the colour space is not uniform.
ClELAB system correlates closely with colour change as perceived by the human eye.
Two different base glasses were chosen. The composition of these glasses is shown in Table 1. Themeltingfurnace was an electrically heated pot furnace with SiC elements. The melting atmosphere was normal room air. H i-alumina crucibles were manufactured by slip casting and fired to 1300 C. 300 g of the base glass was melted in the crucible at 1450 C and the glass was then poured onto a steel plate and the formed sample annealed.