Cubic Zirconia (CZ)
Cubic Zirconia (CZ) is a diamond look alike, existing in small quantities in nature, but normally created by man typically in a colourless form. This material is made from zirconium dioxide ZrO2 and is optically flawless and has a hardness of around 8 to 8.5 on the Mohs scale, just slightly below sapphire and ruby which both have a rating of 9.
The visual similarity to a diamond has made this inexpensive material a substitute that is widely used in jewellery. A more recent synthetic competitor to zirconia is moissanite with a hardness of 9.5 just below that of a diamond on 10. Some gemstone testers are unable to differentiate between moissanite and natural diamonds.
With a specific gravity between 5.6 and 6, it is denser than diamond
by a factor of around 1.6 times. Its dispersion, the ability to split
white light into the colour spectrum, exceeds that of diamond. This
gives the stone a very clear and bright look when placed under a white
light source. If exposed to shortwave ultraviolet light a zirconia will
fluoresce a yellow or yellow/green colour.
The majority of cubic zirconia produced are colourless. It is possible to create coloured stones by doping the crystals during manufacture to produce a range of colours. Cerium will result in shades ranging from yellow, through orange to red. Chromium will produce green, neodymium purple, erbium pink and titanium creates a golden brown hue.
Some cubic zirconias are coated with a DLC (diamond like carbon) film to make them appear to be more ‘diamond like’ by reducing the high level of fire normally exhibited by an untreated gem. A ‘Raman Spectra’ test of a treated stone will show a positive diamond signature because of the high percentage of diamond bonds in the coating. A thermal conductivity test will indicate zirconia because of its low rating compared to that of a natural diamond.
Synthetic production began in Russia during the 1970’s which was the first time stones were available at a size suitable for use in jewellery (naturally occurring CZ is too small). The weight of cubic zirconias in measured in carats, the same scale used for diamonds. 1 carat is 200 milligrams. There are 100 points in a carat, so 1 point weighs 2mg.
The process for cleaning cubic zirconias is the same as it is for gold and silver chains or charms. A solution of warm to hot water with a small amount of dishwashing liquid and a soft tooth brush are all that is required. The detergent will break down oils that have settled on the stone and the brush helps to remove them. Getting into the setting and removing built up dirt should be done carefully, so as not to damage the claws holding the stone in place. Rinse under warm to hot running water and dry thoroughly with a soft cloth. Alternatives include ultrasonic and steam cleaners, but most times a little soap and water will be sufficient.