How do you tell this difference between a diamond and cubic zirconia?

There are thousands of tests you can do to find out the difference between cz and diamonds. If you put the gem near your mouth and breath on it, if it takes about 2-5 seconds to defog, then it is most likely cz, but sometimes jewelers put a layer of diamond around cz so it will defog instantly. You can also take the gem, place it upside down on a newspaper, if you can see the writing or anything close to it, it is fake. You can also use a jewelers loupe, cz under a loupe is flawless, diamond has very flaws that you can see. I hope this was helpful.