Diamond & Gold — Melbourne's Fine Jewellery House
You already know the four Cs. You've read about IGI versus GIA. You've watched the YouTube videos comparing brilliance and fire. This guide starts where those leave off — with the specifications that separate a great lab diamond from a merely acceptable one, explained the way we explain them across our Melbourne studio table every single week.
There is a particular kind of buyer — and if you're reading this, you are almost certainly one of them — who arrives at a jewellery consultation better informed than some of the people behind the counter. You have built the spreadsheet. You have compared certificates side by side. You know the difference between IGI and GIA grading standards, and you have views on it. You are, in the most genuine sense, a pleasure to work with, because the conversation can begin at a level that actually serves you.
This guide is written for exactly that person. At D and G company, our Melbourne studio deals in specifics — precise proportions, measurable optical behaviour, the interaction between stone geometry and setting architecture. What follows is the technical framework our own team uses to evaluate and select lab diamonds, shared plainly and without the simplifications that make most buying guides feel patronising to a careful reader.
How to use this guide: Work through it in order. Each section builds on the last, and the ideal specifications for any single factor are always modified by the others. A lab diamond buying guide that treats each spec in isolation produces buyers who optimise for the certificate; this guide aims to produce buyers who optimise for the stone — which is a different, and considerably more rewarding, result.
Part One: Cut — The Architecture of Light
Cut is not decorative. It is structural. Every other specification on a grading report describes what a lab diamond has; cut describes what it does — how efficiently it collects, redirects, and returns light to the viewer. A poorly cut stone with a flawless clarity and a D colour will look flat and inert. An excellently cut stone with more modest specifications will blaze across a room. No other variable in the lab diamond buying guide specs conversation carries this weight.
Table Percentage
The table is the flat facet at the top of the diamond. Table percentage expresses its width as a proportion of the stone's average girdle diameter. Too large and the table dominates the crown, reducing the play of light through the crown facets and producing a diamond that looks bright but flat — technically well-lit but without the complex scintillation that gives a great stone its character. Too small and light return suffers from the opposite problem: the stone darkens in the centre and looks antique in a way that is rarely intentional.
Round Brilliant — Table Percentage
Ideal range: 53% – 58% | Acceptable: 59% – 61% | Avoid: 62% and above, or below 52%
Note that table percentage interacts directly with crown angle — a slightly larger table can be offset by a steeper crown without meaningful performance loss, which is why evaluating any single specification in isolation misses the point. The proportions are a system, not a checklist.
Depth Percentage
Depth percentage measures the height of the stone from culet to table as a proportion of the average girdle diameter. Shallow stones leak light through the pavilion — the familiar "fish-eye" effect, where the reflection of the girdle appears as a dark ring through the table. Deep stones trap light internally, producing a dark, inert appearance often described as "nail-head." Both represent wasted potential in a stone that may otherwise carry impressive paper grades.
Round Brilliant — Depth Percentage
Ideal range: 59% – 62.5% | Acceptable: 58% – 58.9% or 62.6% – 64% | Avoid: Below 57.5% or above 65%
Crown Angle
Crown angle is the angle of the bezel facets relative to the girdle plane. It is one of the two most consequential angle measurements on a grading report — the other being pavilion angle — and the interaction between the two determines almost everything about a stone's optical character.
A crown angle between 34° and 35° paired with a pavilion angle between 40.6° and 41° produces the combination most consistently associated with high brilliance and fire in a round brilliant. Steeper crowns (above 35°) tend to increase dispersion — fire, the coloured flashes — at some cost to brilliance. Shallower crowns (below 32°) compromise both. In our Melbourne studio, crown angle is one of the first sub-grades we check after the headline cut grade, because it is the specification that most reliably predicts how a stone will behave under real-world lighting conditions.
Round Brilliant — Crown Angle
Ideal range: 34° – 35° | Acceptable: 32° – 33.9° or 35.1° – 36° | Avoid: Below 31.5° or above 36.5°
Pavilion Angle
Pavilion angle is the angle of the lower half facets relative to the girdle plane, and it is the single most critical individual measurement in determining light return. The pavilion is where incoming light is redirected back towards the viewer; a pavilion that is too shallow allows light to pass through the back of the stone (the fish-eye again); too steep and light bounces at the wrong angle and leaks out the side.
Round Brilliant — Pavilion Angle
Ideal range: 40.6° – 41° | Acceptable: 40.4° – 40.5° or 41.1° – 41.4° | Avoid: Below 40° or above 41.8°
Frequently Asked
Do these ideal proportion ranges apply to fancy shapes — ovals, cushions, pears?
They do not, and this distinction matters enormously for a specification-driven buyer. The ideal proportions above apply exclusively to round brilliant lab diamonds, where decades of optical modelling and standardised grading have produced agreed benchmarks. Fancy shapes — ovals, cushions, pears, radiants, emeralds — are not subject to the same standardised cut grading system, which means a grading report for an oval lab diamond conveys far less about optical performance than one for a round. The consequence is that fancy-shape selection is genuinely impossible to do well from paperwork alone. Characteristics like bow-tie shadow (a dark, butterfly-shaped area across the centre of an oval or pear caused by light leakage), windowing (see-through transparency in the face-up position), and extinction (dark, dead areas visible when the stone moves) are all real performance deficits that a certificate will not flag. In our Melbourne studio, fancy-shape selection is done in person, stone by stone — and we consider it one of the areas where experienced human assessment adds value that no report can replicate. When clients come in to explore engagement ring styles featuring fancy shapes, we always bring out comparison stones rather than relying on specifications alone.
Part Two: Polish and Symmetry — The Finishing Grades
Polish and symmetry appear at the bottom of most grading reports and receive correspondingly little attention in most buying guides. This is a mistake, though a forgivable one — at the Excellent level in both, the differences are truly microscopic. The caution is at the boundary between grades.
Polish
Polish describes the quality of the surface finish on each facet — the degree to which a trained grader can detect surface irregularities (polish lines, burns, scratches from the polishing wheel) under ten-times magnification. An Excellent polish grade means the surface is effectively flawless under magnification; a Very Good grade means minor surface characteristics are present but do not affect face-up appearance to the unaided eye; a Good grade or below means characteristics that could, in some lighting conditions, reduce the sharpness with which the stone returns light.
Our specification threshold: Excellent. We do not stock lab diamonds with polish grades below Very Good, and we discuss the Very Good/Excellent distinction explicitly with clients when it arises in their shortlist, because the visual difference, though subtle, is detectable under certain lighting conditions — particularly the bright, direct lighting common in photographing engagement rings and, rather more relevantly, in Melbourne's superb natural light.
Symmetry
Symmetry grades the geometric regularity of the facet arrangement — whether facets meet precisely at their intended points, whether the culet is centred beneath the table, whether the girdle undulates within acceptable tolerances. Poor symmetry does two things: it introduces optical asymmetry that the eye detects as a vague unease without being able to identify the cause, and it affects the patterning of light return — the structured alternation of bright and dark areas that gives a well-cut round brilliant its characteristic "arrows" pattern under direct light.
Polish & Symmetry — Recommended Minimum
Target: Excellent / Excellent | Acceptable: Very Good / Very Good (minor visual impact) | Avoid: Good or below in either grade
The practical takeaway: if a stone reaches your shortlist on cut proportions, colour and clarity, but carries a Good symmetry grade, remove it. The visual consequence is real — not dramatic, but real — and at a price point where the specifications matter, there is no reason to accept it.
Part Three: Fluorescence — A Nuanced Reading
Fluorescence is the most misunderstood specification in diamond retail, generating both excessive fear and careless dismissal in roughly equal measure. A technically precise reading of it is worth having.
Fluorescence describes a stone's tendency to emit visible light when exposed to ultraviolet radiation — the UV component in sunlight and in some artificial lighting. In mined diamonds, strong blue fluorescence occasionally causes lower-colour stones to appear whiter in outdoor light, which was historically treated as a minor advantage. In lab diamonds, the fluorescence picture is more varied and requires a growth-method-specific understanding.
Fluorescence in CVD Lab Diamonds
CVD-grown lab diamonds — the majority of stones in today's market — can show a characteristic orange or orange-pink fluorescence under UV light. This is a production artefact specific to the CVD process and has no mined equivalent. The practical implication: in most indoor lighting, this fluorescence is not triggered and has no visible effect. Under UV-rich outdoor light, a stone with strong orange fluorescence can appear slightly warmer or hazier than its colour grade suggests. The effect is real but typically subtle; the more important issue is disclosure — a retailer who does not mention CVD fluorescence characteristics when discussing a stone is either uninformed or choosing not to inform you. At our Melbourne studio, we consider disclosure non-negotiable at any price point.
Fluorescence in HPHT Lab Diamonds
HPHT-grown stones more commonly show blue or blue-green fluorescence, closer in character to mined diamond fluorescence. Strong blue fluorescence in an HPHT lab diamond can, as with mined stones, make certain colour grades face up whiter in outdoor light — which, for some buyers with modestly graded colour stones, is a genuine optical benefit rather than a concern. The nuance is that very strong fluorescence of any colour can, in a minority of stones, contribute to a slightly milky or haziness in direct sunlight — a characteristic graders call "over-blue." Seeing the stone under varied lighting conditions is the only reliable way to assess this, which is another reason that online-only stone selection has meaningful limitations for a careful buyer.
Fluorescence — Practical Guidance
None / Faint: No meaningful impact; proceed on other specifications. | Medium Blue (HPHT): Typically neutral to mildly beneficial; view in varied light. | Strong / Very Strong (any colour): View the specific stone outdoors before committing. | Orange / Orange-Pink (CVD): Confirm disclosure; view in natural light; note the metal and setting interaction.
Frequently Asked
Should I specifically seek out or avoid fluorescence in a lab diamond?
Neither position, held categorically, is defensible. Fluorescence is a characteristic to be assessed in context — the specific stone, the specific fluorescence colour and strength, the setting metal, and the lighting environments the ring will primarily inhabit. For buyers choosing yellow gold settings, the distinction between a D-colour stone and an H-colour stone in terms of face-up whiteness is largely neutralised by the setting's reflection — and in that scenario, the modest premium paid for a high colour grade is difficult to justify visually. For buyers choosing platinum or white gold with strong aesthetic preference for face-up whiteness, colour grade matters more and fluorescence interactions warrant closer scrutiny. The most useful thing we can do in our Melbourne studio is show you the specific stone you are considering under multiple light sources — LED, incandescent, and, when the Melbourne sky cooperates, direct natural light — before a decision is made. No specification tells that story better than the stone itself does.
Part Four: The Comprehensive Spec Reference Table
The following table consolidates the ideal, acceptable and avoid ranges for a round brilliant lab diamond. For fancy shapes, treat this as directional reference only — as noted above, fancy-shape assessment requires physical evaluation.
| Specification | Ideal | Acceptable | Avoid |
|---|---|---|---|
| Cut grade | Excellent / Ideal | Very Good (upper range only) | Good or below |
| Table % | 53% – 58% | 59% – 61% | ≥62% or ≤52% |
| Depth % | 59% – 62.5% | 58% – 58.9% or 62.6% – 64% | ≤57.5% or ≥65% |
| Crown angle | 34° – 35° | 32° – 33.9° or 35.1° – 36° | ≤31.5° or ≥36.5° |
| Pavilion angle | 40.6° – 41° | 40.4° – 40.5° or 41.1° – 41.4° | ≤40° or ≥41.8° |
| Polish | Excellent | Very Good | Good or below |
| Symmetry | Excellent | Very Good | Good or below |
| Colour | D – F (colourless) | G – H (near-colourless) | I – J in stones above 1.5ct without assessment |
| Clarity | VS1 – VS2 (eye-clean) | SI1 if confirmed eye-clean in person | SI2 or below without physical assessment |
| Fluorescence | None – Faint | Medium (assess in natural light) | Strong without physical assessment |
| L/W ratio (ovals) | 1.30 – 1.50 | 1.25 – 1.29 or 1.51 – 1.60 | Below 1.20 or above 1.65 |
Part Five: What the Specs Cannot Tell You
A technically informed buyer sometimes arrives at a decision point where two stones on paper look effectively identical: the same cut grade, overlapping proportions, equivalent colour and clarity. This is the moment where the specification framework, having done its excellent job of eliminating inferior options, hands the decision back to the human in the room.
"The ideal proportions get you to the shortlist. The shortlist gets you to the stone. The stone makes the decision — not the certificate."
Two things distinguish truly exceptional lab diamonds from those that meet every benchmark but nothing more. The first is face-up appearance — whether the stone, held at arm's length, delivers the complex interplay of brilliance and fire that photographs poorly but registers immediately in person. The second is what jewellers privately call "character" — an indefinable quality that relates to how the stone's scintillation pattern animates with movement, how its brightness distributes across the table and crown, whether it reads as alive or merely bright. Both require a human eye, in real light, with the actual stone.
This is why our Melbourne studio insists on physical stone assessment before every significant purchase. When clients come in to build own engagement ring designs, we bring comparable stones from the current inventory and place them alongside each other under our assessment lighting before any stone is set. The comparison takes minutes. Its effect on the quality of the final decision is significant.
Part Six: Applying the Framework — Setting, Metal and the Ring as a System
A technically excellent lab diamond in a poorly considered setting is a diminished thing. The specification framework above is a stone-evaluation tool, but the ring is more than the stone — and the decisions made around the stone affect its performance as much as the stone's own proportions do.
Setting Consideration One
Claw Height and Light Entry
Claws that sit too low on the girdle block light entry into the crown facets, reducing the stone's effective brilliance. Claws that sit too high create a profile that looks structurally heavy rather than elegant. In our Melbourne workshop, claw height is set specifically for each individual stone's girdle thickness — not adapted from a generic template — which is one of the visible quality differences between a locally crafted ring and an imported mass-market setting.
Setting Consideration Two
Metal Colour and Stone Colour Interaction
As noted in the colour section: yellow gold reflects warmth into a stone, making colour grade less perceptible at the face-up position. Platinum and white gold are optically neutral and allow the stone's true colour to read. An H colour stone that looks near-colourless in a yellow gold solitaire may read fractionally warmer in platinum, depending on the individual stone and the lighting. This is not a problem; it is a system interaction that is worth understanding when balancing colour grade against budget, particularly in the context of our collection of economical engagement rings where specification decisions carry meaningful budget implications.
Setting Consideration Three
Gallery Design and Light Passage
The gallery — the underside structure of the setting between the claws — determines how light reaches the pavilion from below. An open, minimal gallery allows ambient light to enter from all angles, contributing to the stone's brightness in diffuse lighting. A heavy, closed gallery is structurally simpler to manufacture but optically inferior. In the context of the difference between high jewellery vs fine jewellery — the former defined by extraordinary material and labour investment, the latter by quality executed at a considered price point — gallery design is one of the specifications that genuinely distinguishes the two in practice, not merely in price.
Frequently Asked
Once I've found my ideal stone, what should I know about the ring going forward — sizing, maintenance, and care?
Three practical points worth embedding from the outset. First, sizing: have the ring sized accurately at the time of purchase by the same workshop that crafts it. Finger size varies by temperature, time of day, and season — morning sizing tends to read smaller than evening — so a skilled fitting appointment takes all of this into account. Our published ring resizing cost covers in-house adjustment by the same craftsmen who made the ring, which preserves the integrity of the setting in a way outsourced resizing cannot always guarantee. Second, maintenance: a professional clean and claw check once a year is the minimum for a ring worn daily; more frequently if the wearer is physically active. Lab diamonds accumulate the same oils and residues as any stone, and a clean stone consistently outperforms a dirty one under every lighting condition — sometimes dramatically so. Third, and perhaps most importantly for the long-term relationship with your ring: know where it was made and by whom. The Melbourne provenance of a locally crafted ring means a physical workshop, a continuous relationship, and craftsmen who understand the specific architecture of your piece when it eventually needs attention — which, over a lifetime of wear, it will.
The Spec Guide Checklist
Before committing to any lab diamond, work through this sequence:
- Confirm the laboratory: IGI or GIA for lab diamonds; understand that IGI grades the majority of lab stones and that minor grade differences between the two laboratories are documented and worth researching.
- Check cut grade and sub-grades: Excellent headline grade; table 53–58%; depth 59–62.5%; crown angle 34–35°; pavilion angle 40.6–41°.
- Confirm polish and symmetry: Both Excellent. Remove any stone with a Good grade in either from the shortlist without exception.
- Assess colour in context: Choose the colour grade for the setting metal and carat weight, not in isolation. D–H covers virtually every practical scenario.
- Confirm eye-cleanliness in person: SI1 and above on paper; confirmed eye-clean with the actual stone at arm's length, in normal lighting, not under a loupe.
- Ask about fluorescence and growth method: CVD or HPHT; fluorescence colour and strength; any post-growth treatment performed and disclosed.
- See the stone under varied light: LED, incandescent and natural daylight. Melbourne's light is unforgiving and unambiguous — it will tell you what the certificate cannot.
- Evaluate the setting as part of the system: Claw height, gallery design, metal choice. The ring is the final product; the stone is the centrepiece of a larger craft decision.
When you bring this framework into our Melbourne studio — whether you are selecting a significant solitaire or exploring how it relates to future gents wedding rings to complete the set — the conversation can begin exactly here, at specification level, without the introductory simplifications that waste a careful buyer's time.
We do not ask you to trust us instead of the specifications. We ask you to trust us and the specifications — because twenty years of selecting lab diamonds in Melbourne has taught us that the two, working together, produce a result that neither can achieve alone.