A ring described as a 40-point diamond may come with details such as about 0.40 ct, K color, “SL1,” 2EX, no fluorescence, crystal/feather inclusions and an 18K gold setting. But two details must be checked before any price comparison: the report is written as GLA, not GIA, and “SL1” is not the standard GIA clarity grade “SI1.” It may be a typing error, a local report abbreviation or something else.
Verify the report before valuing the ring
The GIA diamond grading report guide illustrates the fields used in GIA diamond grading, including weight, colour, clarity, measurements and applicable cut or finish information. The fields and grading scope depend on the report product; not every diamond shape receives an overall cut grade. The GIA natural diamond reports and services also shows that GIA report types have specific conditions and are for loose natural diamonds in defined ranges. Check the issuer’s full name and the printed clarity field. Similar-looking letters do not establish which laboratory or grading scale was used.
Fields that change value
- Report issuer: GLA, GIA, NGTC, IGI and other names do not carry the same market weight.
- Clarity: confirm whether it is SI1, SL1, or another local code; the wrong letter changes comparisons.
- Shape: round, princess, oval and other cuts price differently.
- Natural or lab-grown: missing origin/type information can change resale value dramatically.
- 2EX: check which two fields are Excellent—cut, polish, symmetry or something else.
- Setting: 18K gold weight, condition, brand and workmanship add value, but usually not the same way as the center diamond.
A comparison workflow with numbers
- Transcribe the report exactly: issuer, report number, shape, measurements, carat, color, clarity, cut, polish, symmetry, fluorescence and comments.
- Find 5–10 current listings with the same report tier and close specs: for example, 0.38–0.42 ct, K color, confirmed SI1 if that is what the report truly says, same shape, same natural/lab-grown status.
- Separate the diamond from the ring: compare loose-stone asking prices first, then add the 18K setting’s realistic second-hand value and workmanship/brand premium if present.
- Discount for resale: a private resale offer is usually lower than retail replacement price because the buyer takes liquidity and verification risk.
For example, if three comparable confirmed natural round 0.40 ct K/SI1 stones from the same report tier cluster around one price band, but your report is a weaker lab name or the grade is actually lower than SI1, use a lower band. If the ring is lab-grown, fancy-shaped, chipped, or lacks a verifiable report number, the comparison set must change.