The Yingyang Bianstone facial can be heated by hot water, hot air, or simply by exposing it to sunlight; or cooled using cold water. After being heated or cooled, it can be applied for scraping on the head or face or neck to improve your skin complexion.
As it has natural infrared, it is not a must to heat the bianstone, just use it to scrape immediately anytime you like.
Heating or cooling depends on your requirement. It is not a must.