Results obtained by the L*a*b* colour system
suggested the following observations. As already
known, the L* values range from 100 (white) to 0
(black); negative or positive values for a* denote a
green or a red shift, respectively, while negative or
positive values for b* denote a blue or a yellow shift.
All the measured a* values were negative, showing a
general green shift. Samples warmed up to 1 050 °C,
type A, visually observed as light green, and sample
B950r (pale green) denoted a strong green shift;
samples described as pale greyish green did not record
a similar shift. Both negative and positive values were
observed for b* values. All blue observed samples
denoted negative b* values, while for green observed
samples only positive b* values (‘yellow’ values) were
measured.