Rob Cornfield
Cofounder. Diamond sourcing and cut specialist. Rob helps you understand what the actual stone shows beyond the headline grades.
Cut, sourcing, and the evidence behind the stone
35+ years of experience in the diamond trade
Rob Cornfield · Your Diamond Guys
Rob checks the diamond behind the grade
Rob Cornfield is a cofounder of Your Diamond Guys with 35+ years of experience in the global diamond trade. His work focuses on sourcing, cut quality, light performance, proportions, and inclusion concerns.
The report is the starting point. Rob looks at how the available measurements, images, and video support the buying decision. A high grade does not remove the need to check the actual stone.
From sourcing judgment to buyer guidance
Sourcing teaches a practical lesson: similar grades do not make diamonds interchangeable. Cut, spread, transparency, and inclusion location can change which stone deserves attention before the buyer ever sees a price comparison.
That is the perspective Rob brings to Your Diamond Guys. He helps buyers connect the technical details to a useful next step, whether that means keeping a candidate, comparing another diamond, or asking for better evidence.
Rob's role complements Josh Allen's work on budget, retailer choice, and the wider purchase. You can read the company background on About Your Diamond Guys.
What Rob focuses on
| Area | The buying question |
|---|---|
| Cut and proportions | Do the measurements work together, and does the visual evidence support them? |
| Light performance | What do brightness, contrast, leakage concerns, and movement show? |
| Visible size | Does the diamond face up well for its weight? |
| Clarity and inclusions | Where is the feature, can you see it, and does it raise a durability or transparency concern? |
| Fancy shapes | Does the outline, bow tie, windowing, or facet pattern create a problem for this buyer? |
| Hearts and Arrows claims | Does the seller provide actual pattern and performance evidence? |
The goal is to make the evidence understandable. You do not need to become a cutter to ask whether a diamond earns its price.
The review starts with the right evidence
For natural diamonds, Rob starts with GIA. He reads the report in context and looks for actual images or video that help answer the remaining questions.
Our diamond review method sets out the starting ranges for natural round brilliants and explains why fancy shapes need different checks. It also names the inclusion concerns we investigate, including bruise, chip, cavity, knot, etched channel, and indented natural.
Numbers narrow the field. They do not give an online reviewer physical access to the stone. An unresolved question stays unresolved until there is evidence to answer it.
Read Rob's approach in practice
Start with table and crown pairing to see why a preferred table percentage does not settle the cut decision by itself.
The clarity plot guide connects report symbols to the area that needs inspection. Rob's GIA natural diamond report guide explains what the report can establish and what the actual stone still needs to show.
Those subjects share one buying habit: find the reason behind the grade before paying for it.
Bring the question you cannot settle
Send the retailer listing, grading report, price, and any available images or video. Tell us what concerns you. That could be an inclusion, a dark area, unusual measurements, or a premium you cannot explain.
For example, a round can fall inside a preferred table range while the angle combination or visual evidence still needs attention. That is a reason to investigate, not a reason to approve it from the table number alone.
An online review relies on the evidence provided. It does not replace laboratory grading, an appraisal, or physical inspection when one is needed.
A clear relationship with the buyer
Consultations are free. Qualifying purchases through YDG's retailer links can earn a referral commission at no extra cost to you. Read the referral disclosure before following a retailer recommendation.
If you want Rob's perspective on the stone you are considering, book your free consultation. Include the listing and your main question so the conversation starts with the diamond.