An unusual 24 carat piece of gueda type sapphire came into the office a while ago. From an unknown location in Africa, the piece was heavily silky and showed a reddish light-scattering Tyndall effect as shown in the video.
As the piece was performed and lost mass, the Tyndall effect loss the reddish hue and became more greenish-yellow.
Peeking into the oven at 950 degrees centigrade, the piece is under going what the Thais call a “fai raek” [ ไฟแรก ]— a lower temperature heat run, before a secondary higher heating session. The gueda sapphire is giving off an intense bright orange-red glow.