A Guide to Buying Diamonds and Tanzanite

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A Guide to Buying Diamonds and Tanzanite

All you need to know about buying jewellery in Cape Town

What makes a “good” diamond? The aesthetics are important, but also significant is the value. Four “Cs” determine this, and these are the fundamentals you should know when selecting your diamond, according to South African diamond expert Yair Shimansky.

Shimansky has been in the diamond industry for over 30 years and knows everything there is to know about diamonds, Tanzanite and how to craft beautiful jewellery that has lasting value. Shimansky is also one of the most trusted names in South Africa. 

Yellow diamonds with deep colour are very rare and valuable, and look gorgeous paired with white ones. Image: Shimansky


There are four important factors to consider when determining a diamond or Tanzanite’s worth: Cut, colour, clarity and carat. And then one more “c” – confidence. This will weigh up the ethicality of the stone’s journey. Here’s what they mean and how to apply them.

The great thing about diamond shopping at Shimansky is it’s more affordable than you might think. Image: Shimansky


The cut of a diamond is one of the most important of the “Cs”. It affects how light is directed within the stone to increase (or decrease) the sparkle. If the diamond is ideally proportioned and symmetrical, it reflects more light and this increases the value of the stone.

The Evolym ring is a unique design to Shimansky, and is “my love” spelled backwards. Image: Shimansky

The benchmark cut, the Round Brilliant, is based on the optics of diamond designer and engineer Marcel Tolkowsky, who calculated the perfect angle at which a diamond claims “its most vivid fire and its greatest brilliancy”. Shimansky’s internationally patented Brilliant 10 and My Girl cuts are other incredible designs.

The cut of a diamond brings out its brilliance. This is Shimansky’s classic Victoria ring. Image: Shimansky

In terms of Tanzanite, if the cut is too shallow, the shade of violet or blue will be lighter and, therefore, less valuable. Generally, the deeper the cut, the more intense the colour and more valuable the stone. The shapes that yield the best intensity are the Cushion, Oval and Trillant cuts.


The closer a diamond is to being absolutely colourless – with no hint of yellow or brown – the more rare and valuable it is. On the other hand, a stone with a rich yellow, orange, pink, green or blue colour is very rare, and this makes it valuable. Such jewels are called Fancy Diamonds, and are even more expensive than pure white ones.

Opt for either deep colour or no colour – both are valuable. Image: Shimansky

The colour of Tanzanite is predominantly blue or violet, and the more intense this is, the more rare and valuable. What sets this gem apart from many others is the fact that it is trichroic, meaning it displays three colours – violet, blue and red – when viewed from three different angles.

The Trilliant Solitaire tanzanite pendant. Image: Shimansky


Diamonds and Tanzanite may show minute traces of other minerals, which appear as natural imperfections known as inclusions. A stone is rated according to inclusions, known as the “clarity factor”, which gives an indication of how many of these marks there are. The more clear or flawless a diamond is, the more desirable and valuable.

Try for as clear a diamond as you can afford – the less flaws, the more valuable. Image: Shimansky


The carat indicates the weight of a diamond, with one carat being equal to 200mg. The larger the diamond, the higher its carat-weight and the greater its price and worth. However, the value of a stone is not only determined by carat size, but by all of the factors above. So you may, for example, decide to buy a smaller diamond with high clarity and colour or you may opt for a bigger diamond with lower colour and clarity.

One carat is equal to 200mg, and that applies to both diamonds and Tanzanite. Image: Shimansky

Tanzanite is a bit softer, which is why it’s not considered as valuable as a diamond. According to Mohs Scale of Mineral Hardness, it’s vulnerable to scratches, which is why Shimansky doesn’t recommend using it for rings that are worn daily. There are, however, fewer of these stones: Tanzanite is 1 000 times more rare than a diamond and, with only one known source to date, it’s predicted that within the next 10 to 12 years, no more gem-quality Tanzanite will be found. This is why it is a good investment.


​​This is the confidence factor. It’s not yet an official “C” but is still a widely accepted one, and refers to the amount of confidence you have in the jeweller you’re buying from and the assurance that a diamond is as valuable as it is claimed to be. The stone should have been certified by an independent diamond body, like the Gemological Institute of America (GIA) or the European Gemological Laboratory (EGL), and it should come with an authentic certificate, which breaks down the 4 Cs. 

It’s important that the diamond is certified, from its history through to the value. Image: Shimansky

At Shimansky, every diamond is laser inscribed on its girdle with a unique identification number that links the stone to its certificate, which means you can confirm the authenticity and the value of a piece at any time.


There are Shimansky shops in Cape Town, including the V&A Waterfront, Johannesburg and in New York. 

Shimansky, V&A Waterfront 

Shop 6259, Upper Level

Opening hours: daily 9 am - 9 pm

Shimansky Showroom

Level 1, The Clocktower, V&A Waterfront

Opening hours: Mon-Sun, 9am - 5pm


Follow Shimansky on Instagram:



Shimansky stores are full of jewels for special moments.

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Shimansky’s showroom is in the V&A Waterfront; here’s a guide to the precinct.


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