One of the ways to identify the quality of quartz tubes is annealing. The conventional method of annealing is to place the quartz tube in a constant temperature furnace. The temperature gradually drops from 1000°C to 1200°C to 0°C.

The reason for the discoloration of the quartz tube after annealing is that the content of metal elements in the quartz tube material exceeds the standard. When heated to a certain high temperature, metal elements will oxidize rapidly. So the black or white stuff you see on the surface of the tube is the metal oxide.

Can color change quartz tubes be used? It depends on the usage environment. Under the requirements of high temperature and high light transmittance, this must not meet the requirements. But if only high temperature resistance is required, this color changing tube can also be used. Exceeding the standard of trace elements will not significantly reduce the high temperature resistance of the quartz tube. In short, if we only have high temperature resistance requirements, we can choose a quartz tube with too much metal content. Because it costs less.