Partially dissolved rutile silk in a Vietnamese ruby. The partially dissolved silk is

 indicative proof the stone has been heated to high temperatures.

 

 

White clouds are a common inclusion in heat-treated rubies from Mong Hsu.

 

 

A heat-treated Mong Hsu ruby clearly showing the white cloudy area.

 

 

Another heated Mong Hsu ruby with characteristic white cloudy inclusions.