Gold filled is an actual layer of gold-pressure bonded to another metal, such as Brass.
Gold filled is always confused with gold plating. But Gold filled is much more valuable and tarnish resistant than Gold plated.
Cubic Zirconia (CZ) is so simmilar looking to a diamond, that only a expert can differentiate between the two.
There are a few features of a CZ which distinguish it from diamond, observable only under the microscope.