Diamond education

Diamond Buying Guide

Choosing the right diamond can feel overwhelming, but with the right knowledge it becomes exciting. This guide explains everything you need to know — from the 4Cs (cut, colour, clarity and carat) to certification, sparkle, and price. Whether you’re considering a natural or lab-grown diamond, our expert advice will help you buy with confidence. As an Adelaide jeweller, we guide clients through every step of the diamond buying process.

01 / Foundations

What is a Diamond?

Diamonds are the hardest known natural mineral, formed over billions of years beneath the Earth’s surface. Under intense heat and pressure, carbon atoms bond in a crystal structure that results in the unique strength and brilliance of a diamond. These rare stones are transported to the surface by volcanic activity, making each diamond a remarkable product of time and nature.

Diamonds are ideal for engagement rings, with a perfect 10 on the Mohs hardness scale. Their durability makes them resistant to scratches and everyday wear.

02 / Diamond grading

Understanding the 4Cs of Diamonds

Not sure where to start? Book a consultation with Carmen & Lucy for expert guidance tailored to your preferences.

Originally developed by the Gemological Institute of America (GIA), the 4Cs — Cut, Colour, Clarity, and Carat — form the global standard for evaluating diamond quality. Each element plays a distinct role in the look, value, and performance of a diamond:

Cut Graded from Excellent to Poor (GIA) or Ideal to Poor (IGI), cut determines a diamond's ability to reflect light and create sparkle.

Colour Ranges from D (colourless) to Z (noticeable yellow or brown tint).

Clarity Assesses the presence of internal inclusions and surface blemishes.

Carat Measures the diamond's weight, with 1 carat equalling 200 milligrams.

03 / Cut

Cut

Cut is the most important factor influencing a diamond’s brilliance. It refers to how well a diamond has been shaped and faceted to reflect light. Unlike carat, colour or clarity — which occur naturally — cut is determined by the skill of the diamond cutter.

A well-cut diamond reflects light to the viewer’s eye in a pattern of sparkle, fire, and brilliance. Diamonds graded Excellent (GIA) or Ideal (IGI) return almost all light that enters the gem, making them appear bright and lively. Poorly cut diamonds allow light to leak from the sides or bottom, leading to a dull appearance.

Learn More About Diamond Cut

04 / Colour

Colour

Colour in diamonds refers to how colourless the stone appears. The less colour, the rarer and more valuable the diamond. The GIA colour scale runs from D (completely colourless) to Z (light yellow or brown). Diamonds with colour outside this range — such as vivid pinks or blues — are considered fancy coloured diamonds.

As carat weight increases, colour can become more noticeable. When choosing a diamond, consider:

Metal choice (yellow gold may mask warm tones, while white metals enhance coolness)
Diamond size (larger stones can show colour more clearly)
Diamond shape (step cuts like emerald or asscher tend to highlight colour, while brilliant cuts disperse light and can mask it)

Learn More About Diamond Colour

05 / Clarity

Clarity

Clarity assesses how free a diamond is from internal inclusions and surface blemishes. The GIA clarity scale ranges from Flawless (FL) to Included (I3). Most diamonds fall somewhere between — and many inclusions are microscopic, having no impact on appearance without magnification.

The type, size, and location of an inclusion influence a diamond’s clarity grade. For example, an inclusion under the table (top facet) is more visible than one near the edge. This is why it's important to view diamonds individually — not all SI1s or VS2s are equal.

Learn More About Diamond Clarity

06 / Carat

Carat

Carat refers to a diamond's weight, not its size. One carat equals 200 milligrams. Two diamonds of the same carat weight can look different in size based on cut and shape. A well-proportioned diamond will often appear larger than one with a deep pavilion or overly thick girdle.

To maximise value, consider diamonds just under key thresholds (e.g. 0.90ct instead of 1.00ct), where prices tend to drop without a noticeable size difference.

Learn More About Diamond Carat

07 / Shape

Diamond Shape

Want help comparing shapes or choosing the best one for your design? Get in touch and we’ll prepare a selection just for you.

Shape refers to a diamond’s physical outline — round, oval, pear, marquise, emerald, and more. Shape affects price, light performance, and style.

Round brilliants remain the most popular due to their superior light reflection.
Fancy shapes (anything non-round) such as oval, pear, and marquise tend to appear larger per carat and often cost less.
Shape also impacts:

Durability (shapes with pointed tips need protective settings)
Visual proportions (elongated shapes can slim the finger)
Price (fancy shapes typically offer better value per carat)

Learn More About Diamond Shape

08 / Origin

Types of Diamonds

Natural Diamonds: Formed naturally over billions of years under the Earth's crust. Composed almost entirely of carbon, they are the only gemstone made from a single element. Prized for their rarity, strength, and enduring value, natural diamonds are often passed down through generations.

Lab-Grown Diamonds: Share the same chemical, physical, and optical properties as natural diamonds. The only difference lies in origin: lab diamonds are grown in specialised laboratories using HPHT or CVD methods. Lab-grown diamonds are real diamonds, indistinguishable to the naked eye — and often more affordable.

Learn More About Lab-Grown vs Natural Diamonds

09 / Certification

What is a Certified Diamond?

Certified diamonds are graded by independent laboratories like GIA, IGI, HRD or GCAL. Certificates verify a diamond’s quality based on the 4Cs and may include diagrams of inclusions and proportions.

At Carmen & Lucy, all diamonds above 0.50ct are typically certified unless requested otherwise for cost reasons.

10 / Pricing

How Much Does a Diamond Cost?

Diamond pricing depends on rarity and quality. Higher grades in cut, colour, clarity or carat translate to higher value. Lab-grown diamonds are generally more affordable due to their availability, while natural diamonds are rarer and hold enduring value.

If you'd like tailored pricing advice, contact us directly — we're here to help.

11 / Sparkle

What Makes a Diamond Sparkle?

A diamond’s sparkle comes from its ability to interact with light. The three key effects are:

Brilliance: White light reflected from the interior and surface
Fire: Flashes of rainbow colour from dispersed light
Scintillation: Patterns of light and shadow seen when the diamond moves

These effects are determined by cut quality. A well-cut diamond reflects light back through the crown, enhancing sparkle. Poorly cut diamonds allow light to escape, appearing dull.

Frequently Asked Questions

What should I look for when buying a diamond?

The 4Cs — cut, colour, clarity and carat — are the global standard for assessing diamond quality. Of these, cut has the greatest influence on sparkle and brilliance, so we recommend prioritising cut first, followed by colour, clarity and carat weight depending on your preferences and budget.

Are lab-grown diamonds real diamonds?

Yes. Lab-grown diamonds are chemically and optically identical to natural diamonds — they’re simply created in a laboratory rather than the earth. The only difference is their origin, making them an excellent option for those seeking beauty and durability at a more accessible price point.

How much should I spend on a diamond?

There’s no set rule for how much to spend. The best approach is to establish a budget that feels comfortable and focus on the factors that matter most to you — whether that’s size, brilliance or rarity. Our Adelaide consultations are designed to guide you through options within your budget, obligation-free.

Do I need a certificate when buying a diamond?

A certificate from a trusted laboratory such as GIA or IGI provides independent verification of your diamond’s quality. Certificates typically include details on the 4Cs, proportions and inclusions, giving you confidence and peace of mind. At Carmen & Lucy, most diamonds over 0.50ct are supplied with certification.

Where can I buy diamonds in Adelaide?

Carmen & Lucy Fine Jewellery specialises in sourcing diamonds through private, appointment-only consultations in Adelaide. We’ll present a handpicked shortlist of diamonds matched to your design vision and budget, ensuring the process feels personal, transparent and enjoyable.

Contact us to receive a personalised shortlist of handpicked diamond options tailored to your preferences and budget. Our consultations are collaborative, informative, and obligation-free — designed to make your diamond search seamless and enjoyable.

Prefer to browse? Explore our online Gem Vault to view the colourful and unique loose stones we’ve curated — ready to be set into your bespoke design.