How to Spot a CZ or Cubic Zirconia

It is unlikely that you will need to verify for cubic zirconia or CZ if you are buying diamond from a reputed jeweler.

However, in case you are considering buying an antique or heirloom ring from some other source, don’t be surprised if you come to know that original stone has been replaced with a CZ. This is because we often encounter imitations in old pieces.

So let’s understand the ways that can help to spot a CZ. Below are few of those.

If the stone is not mounted, or if it can be easily removed from the setting, then have it weighed.

If the weight of the stone in question is much more than the diamond of same size, then surely it is not a diamond. Cubic Zirconia is approximately 75% heavier than a diamond of same size. Let me explain by an example.

6.5mm diamond weighs 1 carat, while same sized CZ weighs 1.75 carats. So a CZ that looks like a 1 carat diamond in terms of its size will actually weigh 1.75 carats.

Check the Girdle of stone.

If the stone is CZ, then its girdle will appear to be frosted. The stone will have a subdued whiteness resembling slightly wet or oiled frosted glass. While, in diamond girdle is transparent and sparkling.

Girdle is the edge or border of the stone that forms its perimeter. It is the edge formed where the top portion of the stone meets the bottom portion – its “dividing line”. This is the part usually grasped by the prongs of the setting.

Do the Thermal Test of stone

CZ is a thermal insulator which means it retains heat more compared to diamond which is thermal conductor (opposite of insulator). So, this property can be used to know the difference between CZ and diamond.

If you exhale from mouth on diamond, it will instantly become clear because of the quick heat loss. On the other hand, if exhaling is done on CZ, it remains cloudy for a while because of slow heat loss.

Newspaper Test

This is the most common and time-tested test and performed commonly by experts to differentiate between diamond and cubic zirconia. It uses refractive properties of these stones to make a distinction between them.

As diamond has higher refractive index (i.e. more bending of light while passing through diamond), so when it is kept over newspaper, it becomes totally impossible to read the letters through it. On the contrary, newsprint can be read through cubic zirconia.

Internal Flaws

Diamonds being found naturally come with inclusions (internal flaws) and usually yellowish to brownish color tinge (due to presence of traces of nitrogen in varying proportion), while cubic zirconia being made synthetically are free from internal flaws and can be made virtually colorless.

Return from Spot a CZ to Diamond Formation page

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