Colorless glass is sometimes used to imitate diamonds. Some of the ways you can tell if a stone is glass are as follows:

• round, oval or donut-shaped gas bubbles
• concave facets
• rounded facet edges - real diamonds have sharp edges and junctions

Large bubbles visible to the naked eye are the best indicator of glass.

Don't care if it's fake? Modern-day fake diamonds such as cubic zirconia (CZ) or moissanite are hard to tell from the real thing and can offer good value. Check out the links below if you're interested in buying fake diamonds: