Why Vintage Engagement Rings Never Go Out of Style

If you have ever compared two diamonds of the same carat weight and found a price difference of thousands of dollars, or looked at a 2 carat diamond and wondered why it costs four times as much as a 1 carat diamond rather than twice as much, this guide answers both questions. Diamond pricing is more structured and more counterintuitive than most buyers expect and understanding how it actually works is the single most useful thing you can do before buying a diamond ring. The short answer is this: diamond price does not scale linearly with carat weight. It scales exponentially, with significant price jumps at specific weight thresholds, and carat weight is only one of four quality variables that together determine the final price. A full understanding of how diamond price is calculated requires understanding all four of these variables, how they interact, and crucially at exactly which carat thresholds the price steps up sharply rather than gradually. A 2 carat diamond does not cost twice as much as a 1 carat diamond at the same quality grade. It typically costs three to five times as much. Diamond pricing is exponential, not linear and this is by design, not by accident. The Carat — What It Measures and Where It Comes From A carat is a unit of weight. One carat equals exactly 0.2 grams. One carat is subdivided into 100 points so a 0.50 carat diamond is also described as a 50-point diamond, and a 0.75 carat diamond as a 75-point stone. The carat system dates to antiquity, when merchants used carob seeds remarkably consistent in weight  as counterweights to measure gemstones. The word 'carat' derives directly from the Arabic word for carob. The modern carat was standardised internationally in 1907 at exactly 200 milligrams (0.2 grams). Before standardisation, carat weights varied between trading regions, creating significant inconsistency in the gem trade. The 1907 standardisation made carat weight the universal, objective measurement it is today the only fully objective variable in diamond grading, because weight is a physical measurement that cannot be influenced by grading opinion. Why Diamond Price Is Exponential, Not Linear The exponential relationship between carat weight and price reflects two compounding factors: rarity and demand concentration. First, rarity. Larger diamonds are exponentially rarer than smaller ones. Diamond rough forms in the Earth's mantle under conditions of extreme heat and pressure over millions to billions of years. Larger diamond crystals form less frequently than smaller ones. Among the diamonds mined globally, stones large enough to yield a 1 carat polished diamond are already uncommon. Stones large enough to yield a 2 carat polished diamond are substantially rarer. Stones that yield 3, 4, or 5 carat polished diamonds are exponentially rarer still — not simply twice or three times as rare, but orders of magnitude rarer. Second, demand concentration at round number thresholds. Buyers globally fixate on specific carat weights: 0.5 carat, 0.75 carat, 1.0 carat, 1.5 carat, 2.0 carat. A diamond just above these thresholds commands a meaningfully higher price than a diamond just below it, even when the face-up size difference is imperceptible. This demand concentration creates what the industry calls 'magic sizes' price steps that represent the most significant per-carat jumps in the market. The Rapaport Price List — How the Diamond Industry Sets Base Prices The foundation of global diamond pricing is the Rapaport Diamond Report, published weekly by Rapaport Group since 1978. The Rapaport list sets baseline prices for round brilliant diamonds in grids organised by colour grade, clarity grade, and carat weight. All other diamond trade between cutters, wholesalers, dealers, and retailers uses the Rapaport price as a reference point, with actual transactions occurring at a percentage above or below 'Rap' depending on market conditions and stone quality. The Rapaport structure makes the exponential price relationship between carat weights explicit and systematic. The price per carat for a 1.00-1.49 carat diamond at a given quality grade is set at a specific level. The price per carat for a 1.50-1.99 carat diamond at the same quality grade is set at a significantly higher level — not because the quality has changed, but because the supply of diamonds in that weight range is meaningfully smaller. This pricing structure means that crossing a carat weight threshold going from 0.99 carats to 1.00 carat, for example jumps the diamond into a higher Rapaport price bracket for its entire weight. The additional 0.01 carat is not what you are paying for. You are paying for the category threshold. The Rapaport price list is why a 0.99 carat diamond costs meaningfully less than a 1.00 carat diamond of identical quality. The 0.01 carat difference in weight triggers a category threshold. You are buying a diamond just below the magic size, not a lower-quality stone. The Magic Size Thresholds — Where Prices Jump Five carat thresholds create the most significant price steps in the consumer diamond market. Understanding them is the most practical application of diamond pricing knowledge for any buyer: Threshold Price per carat step Face-up size (round) Buyer strategy 0.50 ct (50 pts) Significant jump crossing 0.50 ~5.2mm Buy at 0.45-0.48ct for near-identical appearance, 15-20% less 0.75 ct (75 pts) Moderate jump crossing 0.75 ~5.9mm Buy at 0.70-0.73ct — imperceptible size difference, meaningful saving 1.00 ct — LARGEST JUMP Most significant in consumer market ~6.4mm Buy at 0.90-0.98ct — reads the same, 20-30% price advantage 1.50 ct Major jump crossing 1.50 ~7.4mm Buy at 1.40-1.48ct for near-identical face-up, meaningful saving 2.00 ct Largest premium tier ~8.2mm Buy at 1.85-1.95ct — the per-carat jump at 2.00ct is extreme The 1.00 carat threshold is the most commercially significant. A 0.95 carat round brilliant and a 1.05 carat round brilliant differ in face-up diameter by less than 0.15mm  imperceptible in any real-world viewing condition. The price difference at the same quality grade is typically 15-25%. Buying just below the 1.00 carat threshold is the single most straightforward budget strategy available to any diamond ring buyer. How Carat Weight Interacts With the Other Three Cs Carat weight determines which Rapaport price bracket a diamond sits in, but the three other grading criteria cut, colour, and clarity determine where within that bracket the diamond is priced. Understanding how these interact is essential to reading any diamond price correctly. Cut — The Multiplier That Affects Every Other Variable Cut quality is the single most important quality variable for a round brilliant diamond, and the one with the most direct impact on price at a given carat weight. A GIA Excellent cut diamond at 1.00 carat in G colour and VS2 clarity commands a meaningfully higher price than the same carat weight, colour, and clarity in a GIA Fair cut, because the Excellent cut returns significantly more light and is in genuinely higher demand. For round brilliant diamonds, GIA grades cut on a formal scale from Excellent to Poor. TJ Diamond recommends GIA Excellent or Very Good cut as the minimum at any carat weight below Very Good, the visual performance difference becomes apparent even without gemological training. Prioritising cut above colour and clarity at the same carat weight will consistently deliver a more brilliant ring at the same or lower price. Colour — The Variable Most Affected by Metal Choice Diamond colour grades run from D (perfectly colourless) to Z (visibly warm). At any given carat weight, moving from D to G colour at the same cut and clarity represents a saving of approximately 20-35% depending on the specific grade combination. Moving from D to H or I colour extends this saving to 35-50%. The practical value of colour grade selection depends entirely on the setting metal. In a platinum or white gold setting, a diamond at H or I colour may show a faint warmth visible to a trained eye. In a yellow gold or rose gold setting, the warm metal absorbs and neutralises the diamond's warmth G, H, and I colour diamonds read as colourless. Yellow or rose gold buyers can routinely select one or two colour grades lower than white metal buyers and achieve an indistinguishable visual result, saving significantly at any carat weight. Clarity — When Inclusions Are Visible and When They Are Not Diamond clarity grades run from Flawless (no inclusions visible under 10x magnification) to I3 (inclusions visible to the naked eye). At larger carat weights, inclusions become slightly more visible because the stone's larger face-up area can make internally visible features easier to spot at normal viewing distances. This means the minimum recommended clarity grade shifts somewhat with carat weight: 0.5-0.7 carat: SI1 with good clarity characteristics is typically eye-clean inclusions are not visible without magnification. 0.8-1.2 carat: VS2 is the comfortable minimum for a consistently eye-clean result. SI1 can still work if the specific inclusions are positioned toward the edge rather than under the table facet. 1.5 carat and above: VS2 or VS1 is recommended, because the larger face-up area makes SI1 inclusions more likely to be noticeable under normal viewing conditions. Emerald and Asscher cuts at any carat weight: VS2 minimum required, VS1 or above preferred. Step-cut facets act as transparent windows that reveal inclusions hidden in brilliant cuts. The Price Multiplier Table — How Much Does Each Additional Carat Cost? The following table shows the approximate price multiplier relationship between carat weights for natural round brilliant diamonds at G colour, VS2 clarity, GIA Excellent cut. These multipliers reflect the exponential, threshold-driven pricing structure of the diamond market: Carat weight Approx NZD range Price per carat vs 0.5ct (×) 0.50 ct $2,200–$4,500 $4,400–$9,000 per ct 1.0× 0.70 ct $3,500–$6,500 $5,000–$9,300 per ct ~1.2× 1.00 ct $5,500–$12,000 $5,500–$12,000 per ct ~1.6× 1.50 ct $12,000–$22,000 $8,000–$14,700 per ct ~2.4× 2.00 ct $22,000–$40,000+ $11,000–$20,000 per ct ~3.5× 3.00 ct $50,000–$90,000+ $16,700–$30,000 per ct ~6× G colour, VS2 clarity, GIA Excellent cut, 18ct gold solitaire setting. Indicative NZD retail ranges April 2025. Actual price depends on specific grade combination and setting. The multiplier column makes the exponential relationship explicit. Moving from 0.5 carat to 1.0 carat doubles the stone's weight but increases the price by 1.6 times (at the per-carat level). Moving from 0.5 carat to 2.0 carat quadruples the weight but increases the price by 3.5 times at per-carat rates and the total price increases by approximately seven to nine times. At 3 carats, the multiplier reaches six times the 0.5 carat per-carat rate. How Shape Affects the Price-Per-Carat Calculation The pricing structure above applies to round brilliant diamonds. Fancy shapes oval, cushion, pear, emerald, princess, radiant have their own price-per-carat levels, consistently lower than round brilliants at equivalent quality grades. The reasons are manufacturing-related: round brilliants require the most rough diamond waste of any cut (up to 60% of the original crystal), while fancy shapes follow the natural octahedral crystal form more closely, wasting less material. Round brilliant premium: 20-40% higher per carat than most fancy shapes at equivalent quality. The highest per-carat price of any common diamond shape. Oval, pear, marquise: 10-25% less per carat than round at equivalent quality. Oval delivers additional value through its face-up size advantage a 1 carat oval measures approximately 8×5.5mm versus 6.4mm for a 1 carat round, reading as visually larger on the hand. Cushion, radiant, princess: 15-30% less per carat than round. Square shapes with high sparkle. Princess cut corners require V-prong protection but otherwise carry no additional maintenance consideration. Emerald, Asscher (step-cuts): 15-25% less per carat than round, but require higher clarity grades (VS2 minimum). The clarity premium partly offsets the shape discount at the highest quality grades. The interaction between shape discount and magic size threshold creates the most powerful buying opportunity in the NZ diamond market: an oval at 0.95 carats in G colour, VS2 clarity reads as a 1.15-1.25 carat round on the hand (due to face-up size advantage), costs 20-25% less per carat than a round (shape discount), and sits below the 1.00 carat threshold (avoiding the threshold premium). The combined effect can represent 40-50% less in total spend for a ring that reads as larger than an equivalent-budget round brilliant solitaire. Lab-Grown Diamonds and Carat Weight Pricing The magic size thresholds and exponential price relationships described above apply primarily to natural diamonds. Lab-grown diamond pricing follows a similar exponential structure but at 50-70% lower price levels across all carat weights, and the threshold premium at magic sizes is less pronounced because the supply of lab-grown diamonds is less constrained by natural rarity. Practically, this means the 1.00 carat threshold jump that is so significant for natural diamonds is less acute for lab-grown  the percentage premium for crossing a threshold in lab-grown is typically smaller than for natural. This makes the strategic sub-threshold buying approach less financially critical for lab-grown buyers, though it is still worth considering. More importantly, lab-grown pricing creates an entirely different budget calculation. At $5,000-$6,000 NZD approximately the natural diamond price for a 1.00 carat round in G, VS2, 18ct gold a lab-grown buyer can access a 1.7-2.0 carat round at equivalent quality grades, with the exponential price increase for the natural stone not applying in the same way to the lab-grown equivalent. The Five Strategies That Follow From Understanding Diamond Price Calculation Understanding how diamond price is calculated leads directly to five practical strategies that most NZ buyers are not told before they start shopping: Buy just below magic size thresholds. A 0.90-0.98 carat diamond in excellent cut quality reads identically to a 1.00-1.05 carat stone on the hand. The face-up diameter difference is under 0.15mm. The price saving at the same quality grade is 15-25%. Prioritise cut above colour and clarity. A 1.00 carat diamond in GIA Excellent cut at G, VS2 delivers more visual performance than a 1.00 carat in Fair cut at D, IF. Cut is the variable that most directly determines what you actually see. Choose yellow or rose gold to unlock colour grade savings. At the same carat weight, selecting H or I colour in a yellow gold setting versus G colour in a white metal setting saves 15-25% with no visible difference in the finished ring. Consider the oval over the round for the same carat weight. An oval reads 10-15% larger on the hand than a round of the same carat, costs 10-25% less per carat, and benefits from the same magic size threshold strategies. Use lab-grown at the 1.5-2.0 carat threshold. The natural diamond exponential pricing is most severe at the larger carat thresholds. At 1.5 carats, a natural round in G, VS2 costs approximately $12,000-$22,000 NZD. The lab-grown equivalent is $3,000-$6,000 NZD. The exponential rarity premium for natural diamonds at this weight is where lab-grown delivers its largest absolute saving. Applying These Principles at TJ Diamond At TJ Diamond, every diamond ring price is calculated on the actual cost of the specific diamond sourced at the current market rate plus the craftsmanship of the Auckland studio setting. We do not add retail markup layers between you and the wholesale diamond market. When you book a studio consultation, our jewellers will show you specific diamonds at the carat weights you are considering, with the certificates, and compare them directly a 0.95 carat and a 1.05 carat round at the same quality grade, for example, so you can see and feel the difference (or lack of difference) in person before deciding whether the threshold premium is worth it for your specific ring. We also specifically compare fancy shapes against rounds at the same carat weight and budget point so you can see the oval's face-up size advantage concretely, not just read about it. Understanding how diamond price is calculated puts you in a fundamentally stronger position as a buyer. You will be able to identify where a price is justified by rarity and quality, and where it reflects a threshold premium or a shape premium that a small adjustment in specification would eliminate.  

Every diamond sold with an independent certificate is graded on four criteria: cut, colour, clarity, and carat weight. These four variables are known collectively as the 4Cs a framework created by the Gemological Institute of America (GIA) in the 1940s to standardise diamond grading and give buyers an objective basis for comparing stones. Before the 4Cs existed, diamond quality was assessed subjectively, and buyers had no reliable way to compare diamonds across different sellers. Today, every GIA or IGI certified diamond comes with a grading report that documents all four variables. Understanding what each one means, how it affects the diamond's appearance, and how it affects the price is the foundation of buying any diamond ring well. This article explains each of the 4Cs in plain language, with specific grade recommendations for NZ buyers and the practical price implications of each decision. The 4Cs were invented by the GIA in the 1940s to give buyers an objective language for describing diamond quality. Before them, two sellers could describe the same diamond in completely different ways. After them, G colour, VS2 clarity, Excellent cut means exactly the same thing regardless of which jeweller you are talking to. The GIA — Who Created the 4Cs and Why It Matters The Gemological Institute of America created the 4C grading system and the first standardised diamond grading report in the 1940s under founder Robert M. Shipley. Before GIA certification, diamond grading was entirely subjective one jeweller's 'fine white' was another's 'exceptional blue-white,' and buyers had no objective reference point. The GIA system imposed precise, internationally agreed definitions on colour, clarity, cut, and carat weight, and the organisation established the training and testing standards for the gemologists who apply them. The GIA is a non-profit research and educational institution, not a diamond seller. It has no financial interest in any specific grade outcome, which is why GIA certification is the most trusted independent grading in the diamond industry globally. IGI (International Gemological Institute) is the second most widely recognised grading laboratory, used extensively for lab-grown diamonds. At TJ Diamond, every diamond is independently certified by GIA or IGI before we set it. The First C — Cut Cut is the most important of the four Cs, and the most commonly misunderstood. Cut does not refer to a diamond's shape oval, round, pear, cushion, and so on are shapes, not cuts. Cut refers to the quality of the craftsmanship applied to the facets: how precisely each angled surface has been positioned to interact with light. A well-cut diamond takes light entering through the table facet, reflects it internally between pavilion facets, and returns it directly to the observer's eye as brilliance (white light), fire (rainbow dispersion), and scintillation (the sparkle visible when the diamond or the observer moves). A poorly cut diamond leaks light through the bottom or sides before it can be returned, producing a flat, dim appearance regardless of how high the colour or clarity grade is. Cut is the only one of the 4Cs that is entirely within the cutter's control. Colour and clarity are determined by the diamond's natural formation. Cut is a craftsmanship decision and it is the decision that most determines what you actually see. Cut Grades for Round Brilliants — The GIA Scale For round brilliant diamonds, the GIA grades cut quality on a formal five-point scale: Excellent, Very Good, Good, Fair, and Poor. This is the only shape for which the GIA grades proportional cut quality for all other shapes (oval, cushion, pear, etc.), the GIA grades only polish and symmetry, not the overall cut quality that determines brilliance. GIA Cut Grade What it means Brilliance impact TJ Diamond rec. Excellent All proportions optimal for maximum light return Maximum — the benchmark ✓ Recommended Very Good Minor deviation from ideal — still outstanding Near-maximum, imperceptible difference to Excellent ✓ Recommended Good Noticeable deviation — some light leakage Visible reduction under direct comparison Acceptable minimum Fair Significant deviation — clear light leakage Clearly visible reduction in brilliance Not recommended Poor Major proportion errors Very poor light return Not stocked The ideal cut proportions for a round brilliant — calculated by Marcel Tolkowsky in 1919 and confirmed by over a century of gemological science — are: table percentage 53-58%, depth 59-62.5%, crown angle 33-35 degrees, pavilion angle 40.6-41 degrees. A GIA Excellent cut confirms the stone meets these proportional standards. Cut for Fancy Shapes — No GIA Scale, Visual Assessment Required For oval, cushion, pear, marquise, emerald, princess, radiant, and all other fancy shapes, the GIA grades only polish and symmetry not the overall proportional cut quality that determines brilliance. This means a GIA certified oval diamond can have excellent polish and symmetry but a poorly optimised facet structure that produces a pronounced bow-tie shadow across the centre of the stone. The certificate will not reveal this. Assessing cut quality for fancy shapes requires viewing the stone in person under multiple light sources. This is the most important reason to view any fancy shape diamond before purchasing, and one of the key reasons TJ Diamond's in-person and virtual consultation process exists our jewellers assess cut quality for every fancy shape stone individually before it enters our workshop. The Second C — Colour Diamond colour is graded on a scale from D to Z, where D is perfectly colourless and Z has a clearly visible warm or yellow tint. The scale begins at D rather than A because earlier grading systems had used A, B, and C inconsistently starting at D ensured no pre-existing system could claim equivalence. Grade Category Appearance Practical guidance D–F Colourless No colour detectable even by trained eye under magnification Premium tier — priced significantly above G-H G–H Near-colourless Colour difficult to detect — appears colourless in most settings Most popular tier — excellent value, no visible compromise I–J Near-colourless Slight warmth detectable by trained eye in direct comparison Viable in yellow/rose gold — same visual result at lower price K–M Faint colour Faint warmth visible to untrained eye in some settings Not generally recommended for engagement rings N–Z Light to fancy Visible warm or yellow tint — may be intentional preference Specialty category — or lab-grown fancy coloured stones The Metal Setting Changes Everything About Colour Grade The single most important insight about diamond colour grading is that the correct grade depends on the metal setting, not on an absolute standard. In a platinum or white gold setting, a diamond at H or I colour may show a subtle warmth that a trained eye can detect against the cool white metal. In a yellow gold or rose gold setting, the warm metal tone absorbs and neutralises the diamond's own warmth making G, H, and even I colour diamonds appear as colourless as D or E colour stones in white metal. The practical implication: buyers choosing yellow or rose gold can routinely select one to two colour grades lower than buyers choosing white metal, with no visible difference in the finished ring. The cost difference between G and I colour at the same carat weight and clarity can represent 20-35% of the diamond's price a meaningful saving on any budget. The Third C — Clarity Diamond clarity refers to the presence or absence of internal features (inclusions) and surface characteristics (blemishes). Both form during the diamond's creation process inclusions are internal features such as crystal formations, clouds, feathers, or cavities; blemishes are surface features such as scratches or polishing marks. The GIA clarity scale runs from Flawless to I3: Grade Category What it means Visible to naked eye? FL Flawless No inclusions or blemishes under 10x magnification No — rarest grade IF Internally Flawless No inclusions; minor surface blemishes only No — very rare VVS1–VVS2 Very Very Slightly Included Minute inclusions very difficult to see at 10x No — premium grades VS1–VS2 Very Slightly Included Minor inclusions difficult to see at 10x No — most popular tier SI1–SI2 Slightly Included Inclusions visible at 10x, sometimes to naked eye SI1 often clean; SI2 variable I1–I3 Included Inclusions visible to naked eye, may affect durability Yes — generally avoided The Practical Clarity Minimum — Eye-Clean vs Certificate-Clean The most important clarity concept for buyers is the distinction between eye-clean and certificate-clean. A diamond is eye-clean if its inclusions are not visible to the naked eye under normal viewing conditions (approximately 30cm from the stone, in typical indoor lighting). A diamond can carry a relatively low clarity grade on the certificate and still be completely eye-clean in wear. For round brilliant and most brilliant-cut fancy shapes, SI1 is frequently eye-clean. VS2 is the comfortable minimum for a consistently eye-clean result across all brilliant cuts at any carat weight. FL and IF clarity grades command significant price premiums but deliver no visible benefit to the naked-eye viewer the difference between FL and VS2 is measurable only under 10x magnification. The exception is step-cut diamonds. Emerald cuts and Asscher cuts use large, flat, parallel step-cut facets that act as transparent windows into the stone's interior rather than scattering light as brilliant facets do. These cuts reveal inclusions that would be invisible in an equivalent brilliant cut at the same clarity grade. For emerald and Asscher cut diamonds, VS2 is the recommended minimum clarity grade, and VS1 or above is strongly preferred for the cleanest visual result. The Fourth C — Carat Weight Carat weight is the only objective, measurable variable among the 4Cs a physical measurement rather than a graded assessment. One carat equals exactly 0.2 grams, subdivided into 100 points (a 0.50 carat diamond is a 50-point stone). The carat system was standardised internationally in 1907 at 200 milligrams. Carat weight does not directly determine a diamond's face-up size, because cut proportions affect how much of the diamond's mass is distributed toward the top (visible) surface versus the bottom (hidden within the setting). A well-cut round brilliant of 1.00 carat measures approximately 6.4mm across. A poorly cut round brilliant of the same carat weight may measure 5.9mm the extra mass is in a deeper pavilion rather than visible face-up area. Carat Weight and the Magic Size Threshold Premium Diamond prices do not increase linearly with carat weight. They step up exponentially at specific thresholds 0.50, 0.75, 1.00, 1.50, and 2.00 carats because these are the weights at which buyer demand concentrates. A diamond just above these thresholds commands a disproportionate price premium over a diamond just below it, even when the face-up size difference is less than 0.2mm and imperceptible in wear. The 1.00 carat threshold is the most significant in the consumer market. A 0.95 carat round brilliant in GIA Excellent cut, G colour, VS2 clarity is visually indistinguishable from a 1.05 carat round at the same grades in daily wear. The price difference at the same quality grades is typically 15-25%. Buying just below the 1.00 carat threshold is one of the most effective budget strategies available to any diamond ring buyer. Which of the 4Cs Matters Most? The Priority Order The 4Cs are not equally important, and they are not equally worth spending money on. Here is the priority order for round brilliant diamond buyers: 1. Cut — first, always. A poorly cut diamond in any colour or clarity grade is a worse diamond. A well-cut diamond with modest colour and clarity is a better diamond. GIA Excellent or Very Good cut as the non-negotiable minimum for round brilliants. 2. Carat weight — the most visible variable. The size of the stone on the hand is what most people notice. Within a budget, maximise carat weight after meeting the cut standard. 3. Colour — the variable most affected by metal choice. Choose the setting metal first, then determine the minimum colour grade that delivers a colourless appearance in that metal. G for white metal; H-I for yellow or rose gold. 4. Clarity — the variable with the least visible impact. VS2 is the practical minimum for eye-clean across brilliant cuts. Spending above VS2 for most buyers is spending on certificate quality rather than visible quality. For fancy shapes, cut moves from first to tied with carat weight, because the GIA does not grade cut for fancy shapes and the assessment must be done visually. The specific facet quality of an oval or cushion requires in-person evaluation that no certificate can substitute for. How the 4Cs Work Differently for Lab-Grown Diamonds Lab-grown diamonds are graded on identical 4C criteria to natural diamonds by GIA and IGI. The same cut grades, the same colour scale, the same clarity scale, and the same carat weight measurement apply equally. A GIA Excellent cut, G colour, VS2 clarity, 1.00 carat lab-grown diamond carries exactly the same grades as a natural diamond at those specifications. The practical difference is in the price implications. Lab-grown diamonds at equivalent 4C grades are typically 50-70% less expensive than natural diamonds. This means the budget trade-offs between the 4Cs are less acute for lab-grown buyers it is possible to achieve higher grades across all four criteria simultaneously at the same budget that would require compromise in one or more areas for a natural diamond. Lab-grown diamonds are not a compromise on any of the 4Cs. They are the same material graded by the same standards at a lower price, because production is not constrained by geological rarity. Reading a GIA or IGI Diamond Certificate Every TJ Diamond ring comes with the independent certificate for its diamond. Here is what to look for on the grading report: Shape and cutting style: Confirms the diamond shape (round brilliant, oval, cushion, etc.) and the specific facet arrangement. Measurements: The physical dimensions in millimetres. For a round, minimum and maximum diameter and depth. For fancy shapes, length × width × depth. This confirms the face-up size you are actually getting. Carat weight: The official weight to two decimal places. Cut grade: For round brilliants: the GIA cut grade from Excellent to Poor. For fancy shapes: no cut grade, but polish and symmetry grades (each also graded Excellent to Poor). Colour grade: The letter grade from D to Z. For lab-grown, the same scale applies. Clarity grade: The grade from FL to I3, with a plotting diagram showing the location and nature of inclusions. Fluorescence: Whether the diamond glows under UV light and how strongly. Strong blue fluorescence can slightly affect appearance in daylight conditions. Most buyers should look for None to Faint fluorescence. Report number: The unique GIA or IGI report number verify this on the laboratory's website to confirm the certificate is genuine. The 4Cs in Practice — What TJ Diamond Recommends for NZ Buyers Based on what delivers the best visible result for each dollar spent in the New Zealand market in 2025, TJ Diamond's practical recommendation for most engagement ring buyers is this combination as a starting point: Variable White metal setting (platinum/white gold) Warm metal setting (yellow/rose gold) Cut GIA Excellent or Very Good (round); visual assessment required for fancy shapes Same — cut quality does not vary by metal choice Colour G–H for a reliably colourless appearance H–I — warm metal neutralises diamond warmth, saving 20-35% Clarity VS2 for consistent eye-clean result; SI1 possible with good clarity mapping Same — clarity is independent of metal choice Carat Maximise within budget after meeting above thresholds Same — or buy just below magic size thresholds This combination Excellent cut, G-H colour, VS2 clarity delivers a visually excellent diamond ring at a price point that leaves meaningful budget for the setting and ring style. Spending above these thresholds (into VVS or FL clarity, or D-F colour in a yellow gold setting) goes primarily toward certificate quality rather than visible quality. If you are unsure where to compromise in your specific budget and setting combination, a studio consultation with TJ Diamond's jewellers covers exactly this  we compare specific stones at different 4C combinations so you can see and choose based on actual appearance rather than theoretical grade hierarchies.  

Sparkle is the quality that makes a diamond ring immediately, unmistakably visible. It is what catches light across a room, what photographs brilliantly, what makes a stranger notice your ring before they notice anything else. Every buyer wants sparkle. The question is which diamond cut delivers the most of it and the answer is more specific, and more nuanced, than most jewellers explain. The short answer: the round brilliant cut produces more sparkle than any other diamond shape. The longer answer is that 'sparkle' itself has three distinct components, that some shapes prioritise one component over another, and that the cut quality within any shape matters more than the shape itself. Understanding these distinctions is the difference between choosing a diamond that will sparkle brilliantly in every lighting condition and one that only performs under direct light. Sparkle in a diamond is not one thing. It is three things: brilliance, fire, and scintillation. The round brilliant maximises all three simultaneously. Every other shape makes a different trade-off between them. The Three Components of Sparkle — Defined Before comparing cuts, the three components of sparkle need clear definitions, because different diamond cuts produce different balances of each: Brilliance: The return of white light to the observer's eye from the diamond's interior. Brilliance is what makes a diamond look bright and alive. It is produced by internal reflection between polished facets. A well-cut diamond with optimal pavilion angles returns the majority of light that enters through the table facet back to the observer a poorly cut diamond leaks it through the bottom. Fire: The dispersion of white light into its spectral colours the rainbow flashes visible in a diamond. Fire is produced as light bends (refracts) entering and exiting the diamond's facets. It is most visible in lower lighting conditions and when the observer or the diamond moves slowly. Diamonds with steeper crown angles produce more fire. Scintillation: The pattern of bright and dark areas the sparkle visible when either the diamond or the light source moves. Scintillation has two sub-components: the number of sparkle points (determined by the number of facets) and the contrast pattern between bright and dark (determined by facet size and arrangement). More, smaller facets create more scintillation points; fewer, larger facets create bolder contrast. A diamond that maximises all three simultaneously is the highest-performing diamond for sparkle in everyday conditions. This is what Marcel Tolkowsky optimised when he published his mathematical analysis of the round brilliant cut in 1919 his model calculated the exact facet proportions that maximise the combined return of brilliance, fire, and scintillation for a circular diamond outline. Why the Round Brilliant Delivers Maximum Sparkle The round brilliant's 58-facet design 33 on the crown and 25 on the pavilion was the result of Tolkowsky's 1919 mathematical analysis of diamond optics. The specific proportions he identified (table 53-58%, depth 59-62.5%, crown angle 33-35 degrees, pavilion angle 40.6-41 degrees) create a system where: Light entering through the table facet strikes the pavilion facets at the precise angle required for total internal reflection, bouncing it back upward rather than allowing it to exit through the bottom. The crown facets then return this reflected light to the observer's eye as brilliance and simultaneously disperse it into spectral fire through the smaller crown facet angles. The 33 upper facets and 25 lower facets create 58 individual sparkle points visible as the diamond or the observer moves the maximum scintillation of any common diamond cut. The GIA's formal cut grade scale (Excellent to Poor) exists only for round brilliants because their proportions are precisely mathematically defined. This means round brilliants can be objectively measured against a known standard. A GIA Excellent cut round brilliant is verified to be within the proportional range that produces maximum light return. No other shape has an equivalent formal cut grade for overall performance. Marcel Tolkowsky was 21 years old when he published the mathematical proof for the round brilliant's proportions in 1919. Over a century later, those same numbers remain the standard. The round brilliant's sparkle advantage is not marketing it is mathematics that has been independently confirmed for 105 years. How Every Other Shape Compares — Cut by Cut Each fancy shape makes a specific trade-off between the three components of sparkle, and each has qualities that some buyers will prefer over the round brilliant's balanced maximum. Here is the comparison by shape: Oval — 95% of Round Brilliant Sparkle, 10% Larger Face-Up The oval brilliant uses brilliant-cut facets applied to an elongated circular outline, meaning its light performance is very close to a round brilliant typically estimated at 90-95% of a round's brilliance and fire when comparing equivalent cut quality. The face-up size advantage (approximately 10% more surface area per carat than a round) means the oval distributes slightly more white light across a larger area, and the elongated outline creates a distinctive sparkle pattern that some buyers find more dynamic than the round's symmetric pattern. The oval's primary sparkle risk is the bow-tie effect: a shadow across the widest central section caused by light entering elongated facets and not being returned efficiently from the middle of the stone. In a well-cut oval, the bow-tie is minimal and adds depth. In a poorly cut oval, it is a dark shadow that reduces the ring's visual appeal significantly. This cannot be assessed from a certificate it requires viewing the stone in person. Cushion — Warm, Open Sparkle in Two Distinct Styles The cushion cut's sparkle character depends critically on which of its two facet pattern variants the stone uses. Chunky cushions with larger, well-defined facets produce open, warm flashes of brilliance and fire similar to a round brilliant but with a vintage character. Crushed ice cushions with hundreds of small sub-facets produce a dense, holographic shimmer that is more diffused than the round brilliant's distinct fire flashes. Both variants deliver high sparkle, but they are visually very different. The chunky cushion sparkles in large, distinct bursts visible from a distance and in lower lighting. The crushed ice cushion shimmers continuously with smaller but more numerous light points particularly striking in bright or natural light. This distinction cannot be adequately assessed from photographs and must be evaluated in person with both variants side by side. Princess Cut — Geometric Sparkle With High Light Return The princess cut is classified as a modified brilliant, delivering high light return through its square-outline brilliant-cut facets. Its pavilion chevron patterns (two, three, or four chevron configurations) affect the specific character of the sparkle more chevrons produce more numerous, smaller sparkle points; fewer chevrons produce bolder, more distinct flashes. The princess cut's sparkle performance is generally estimated at 80-90% of a round brilliant's overall light return. The princess cut's square corners are its structural vulnerability both tips of each 90-degree corner require V-shaped prong protection. A setting with inadequate corner protection reduces the diamond's visual performance over time as corner chips or cracks develop. Properly set, the princess cut is a high-sparkle, highly geometric choice for buyers who want the brilliance of a brilliant cut in a square outline. Pear — Brilliant Performance With One Pointed End The pear uses the same facet family as the round and oval, producing comparable brilliance and fire within its teardrop outline. Like the oval, the pear can exhibit a bow-tie effect across its widest central section. Wing symmetry the equal curvature of the two rounded sides of the pear significantly affects both its appearance and its sparkle pattern. An asymmetric pear delivers uneven brilliance across its outline. The pear's elongated outline creates a distinctive directional sparkle that appears to flow from the rounded base toward the pointed tip. For buyers who want brilliant-cut performance in a non-circular, non-rectangular shape, the pear delivers excellent light return with the most distinctive silhouette of any brilliant cut. Radiant — The Only Rectangular Brilliant That Matches Round Sparkle The radiant cut, created by Henry Grossbard in 1977, was the first diamond cut to apply brilliant-cut facets to a rectangular outline with trimmed corners. Its light performance is generally estimated at 85-95% of a round brilliant higher than the princess, closer to the oval because the trimmed corners allow more efficient light return than the princess cut's sharp 90-degree corners. For buyers who want a rectangular diamond with maximum sparkle (rather than the step-cut's reflective depth of the emerald cut), the radiant is the optimal choice. Its trimmed corners also make it safer for daily wear than a princess cut, with less corner vulnerability. Marquise — Maximum Elongation, High Sparkle The marquise uses brilliant-cut facets across its elongated oval-with-pointed-ends outline, delivering good brilliance and fire comparable to other elongated brilliant cuts. Like the oval and pear, the marquise is prone to the bow-tie effect. It also has two pointed tips rather than the pear's one, both requiring V-prong protection. The marquise's distinctive visual quality is the dramatic elongating effect on the finger of all brilliant cuts, it creates the most significant finger-lengthening illusion. Its sparkle is directional, appearing to radiate toward the two pointed tips. Step Cuts — A Completely Different Kind of Sparkle Emerald cuts and Asscher cuts are step-cut diamonds: they use large, flat, parallel facets rather than brilliant-cut triangular and kite-shaped facets. Step cuts do not maximise brilliance and fire in the way brilliant cuts do. What they produce instead is a completely different visual quality: a deep, architectural hall-of-mirrors reflective effect where large facets reflect each other and surrounding light in a way that is quiet, sophisticated, and fundamentally different from brilliant-cut scintillation. If sparkle in the sense of high-contrast, rapidly changing brilliance and fire is the primary goal, step cuts are not the correct choice. Step cuts reward buyers who want elegance and depth over visual intensity. The emerald cut and Asscher cut are among the most sophisticated diamond shapes available, but they require a buyer who understands that their light performance is categorically different from brilliant cuts, not simply less of the same thing. The Sparkle Comparison Table The following table ranks the major diamond cuts on sparkle performance across the three components, and identifies the specific buyer who each shape suits best: Shape Brilliance Fire Scintillation Best for Round Brilliant ★★★★★ ★★★★★ ★★★★★ Maximum sparkle priority. The benchmark. Oval ★★★★½ ★★★★ ★★★★ Brilliant performance + elongation + face-up size advantage Radiant ★★★★ ★★★★ ★★★★ Rectangular shape with brilliant-cut sparkle Cushion (chunky) ★★★★ ★★★★ ★★★ Vintage warmth + brilliant performance Pear ★★★★ ★★★½ ★★★★ Brilliant performance in a distinctive silhouette Princess ★★★½ ★★★★ ★★★★ Square outline with good brilliant performance Marquise ★★★½ ★★★ ★★★ Maximum elongation with good brilliance Cushion (crushed ice) ★★★ ★★★ ★★★★★ Contemporary, diffused shimmer effect Emerald ★★ ★★ ★★ Architectural hall-of-mirrors depth, not sparkle intensity Asscher ★★ ★★ ★★ Geometric X-pattern depth, Art Deco character Why Cut Quality Within Any Shape Matters More Than the Shape The most important principle in diamond cut and sparkle is this: a well-cut oval outperforms a poorly cut round brilliant. The shape hierarchy in the table above assumes equivalent cut quality across all shapes. Below that assumption, the single variable with the greatest impact on actual sparkle in a finished ring is the quality of cutting within whatever shape you choose. For round brilliants, cut quality is objectively measurable via the GIA cut grade. A GIA Excellent cut round brilliant is verified to be within the proportional range for maximum light return. A GIA Fair cut round brilliant is not — and its visual performance will be noticeably inferior regardless of its colour and clarity grades. For fancy shapes all shapes other than round the GIA grades only polish and symmetry, not overall proportional cut quality. A GIA grading report for an oval diamond does not tell you whether the oval is cut for maximum brilliance or whether it has a pronounced bow-tie. A cushion certificate does not distinguish between chunky and crushed ice facet patterns. These qualities require visual assessment in person. This is the most commercially significant reason to view any fancy shape diamond before purchasing. The GIA certificate is a necessary but not sufficient basis for a buying decision in any shape other than round brilliant. The actual light performance of the specific stone requires direct observation under multiple lighting conditions. The Setting's Role in Maximising Sparkle The setting contributes to the sparkle experience in ways that most buyers do not anticipate. Prong settings maximise sparkle by allowing maximum light entry from all directions four or six thin claws hold the diamond at specific points while leaving the majority of the girdle exposed to light. Bezel settings reduce side-light entry, which very slightly reduces sparkle compared to equivalent prong settings under direct comparison, though the difference is not noticeable in everyday wear. Halo settings amplify the total sparkle of a ring significantly, because the surrounding accent diamonds add their own brilliance and scintillation alongside the centre stone. A well-crafted halo with micro-pavé accent stones creates a continuous ring of sparkle that extends the visual impact of the centre stone across a larger face-up area. For buyers who specifically want maximum sparkle visible from across a room, a round brilliant in a halo setting is the most effective combination available. The metal finish of the setting also contributes: a highly polished metal surface reflects light back through the diamond's pavilion from below, adding to the stone's total light input. A brushed or matte finish absorbs some of this back-reflection. For maximum sparkle, a high-polish setting in platinum or 18ct gold is the most technically consistent choice. Which Cut Should You Choose for Maximum Sparkle? The direct answer, ordered by sparkle priority: For maximum sparkle above all other considerations: round brilliant, GIA Excellent cut. The 105-year mathematical standard for light return. No other cut matches it. For maximum sparkle in a non-round shape: oval brilliant, assessed in person for bow-tie. Closest to round brilliant in light performance, with the face-up size advantage and the elongating effect. For maximum sparkle in a rectangular outline: radiant cut, trimmed corners, in-person assessment of cut quality. The only rectangular cut that approaches round brilliant sparkle. For maximum sparkle in a square shape: cushion chunky variant for warm, open flashes; princess cut for more geometric, structured sparkle. Both require in-person evaluation. For sparkle with maximum elongation: pear for a teardrop, marquise for the most dramatic elongation of any brilliant cut. Both require bow-tie and symmetry assessment in person. For sophisticated depth rather than sparkle intensity: emerald cut or Asscher cut. These are not the correct choice if sparkle is the primary goal they deliver something categorically different and equally beautiful, but different. Whichever shape you choose, cut quality is the variable that most determines the sparkle of the finished ring. A well-cut diamond in any brilliant-cut shape delivers outstanding sparkle. A poorly cut diamond in any shape round included does not. The certificate confirms the grade; the stone in person confirms the sparkle. At TJ Diamond, every round brilliant is GIA or IGI certified with a formal cut grade. Every fancy shape diamond is assessed individually by our jewellers for bow-tie effect, symmetry quality, and overall light performance before it enters our Auckland workshop. Book a studio consultation to compare cut quality across shapes in person before deciding.