Some natural sapphires are of such poor quality that they can’t be sold. One way that sellers make up for this is filling the sapphire with lead-glass which masks the poor quality of the sapphire. If you see criss-crossing lines, you may have a real sapphire but it is most likely of low quality. If you are considering buying a sapphire from a jeweler, you should always ask whether the gem is natural or synthetic. The FTC requires that jeweler’s disclose information about any gems that they sell. Don’t be afraid that you will sound critical or uninformed if you ask about a sapphire. It’s your money to spend and you want to know for sure what kind of product you are buying. There are various treatments that are done to sapphires to enhance their color or clarity. While this may make the sapphire look better, you may feel it reduces the natural quality. Treatments are not permanent, so it is good to ask about treatments and how long they will last on the gem. Treatments can be removed to return the gem to its natural look.

How would you rephrase that briefly using Vietnamese?
Quan sát những đường giao nhau bên trong viên Sapphire. Hỏi người bán rằng đây có phải là đá thiên nhiên hay không. Hỏi người bán xem Sapphire này là tự nhiên hay đã qua xử lý.