Water and Density Tests For the water test, drop the earring into a glass of water. A real diamond has a high density and will sink to the bottom swiftly, whereas many fake diamonds and other simulants like cubic zirconia or glass will float or sink more slowly.

You will notice that the hallmark is stamped onto the post of the earring. More delicate diamond earrings might be laser hallmarked—a process which is less invasive but which often appears much lighter on the surface of the item.

Diamond earring markings The earrings have stamps that provide information regarding the type of base metal and its purity level. When it comes to earrings with significant diamond inlays, the carat weight of the stone is also included.