Sintering, that is, heat treatment of gemstones, is a means to change the color and transparency of gemstones by changing the content and valence of pigment ions, adjusting the internal structure of crystals and eliminating some internal defects such as inclusions.

To sum up "burning" briefly: through optimization, ruby and sapphire are "heat treated". At present, most rubies and sapphires on the market are heated. Then correspondingly, "non-combustible", that is, pure natural, without any optimization and treatment.

Ruby is not the same as burning or not.

But nothing more than the following situations _

1. Remove (or dilute) purple, brown or blue tones from rubies to make them purer red.

2. Burn the original light yellow or pink into dark yellow, dark brown, yellow and golden yellow.

3. Burn some milky white, filamentous gray rough stones (geuda) into blue.

4. Turn some dark blue with black into purer blue.

Some light-colored sapphires will darken after burning.

6. Remove some blue and green tones from the yellow bag.

7. Take out the filiform ruby.

8. Stellate red and blue can be burned into precious stones containing more titanium.