Fake Ceylon Sapphires are generally made of glass and thus tend to have air bubbles in it. Observing your Ceylon Sapphire stone with a magnifying glass can help you study the gemstone, and if you find any cluster of air bubbles, chances are that it is either made of glass or has glass added to it to enhance its look.
However, the best way to know the authenticity and quality of a Ceylon Sapphire stone is by consulting a gemstone lab that makes use of high-end technology and skilled gemologists that study these gemstones. At GemPundit, you can find real Ceylon Sapphire verified and certified to be authentic and of the best quality by renowned gemstone laboratories such as IGI, GRS, Gubelin, GIA, C. Dunaigre, etc.