Choosing a diamond is easier when you understand how the Gemological Institute of America evaluates each stone. The GIA set the modern standard for diamond grading and its reports are recognized worldwide for accuracy and independence. Below is an expanded, plain‑English guide you can trust, written for House of Diamonds AZ clients who want clarity before they buy.
Why GIA matters
- Independent and objective. Diamonds are graded without any owner information visible to graders.
- Consistent systems and calibrated environments. Results are repeatable across labs.
- Widely accepted. GIA grading scales for color, clarity, and cut are industry benchmarks.
The grading workflow, step by step
- Intake and anonymization
- Each diamond arrives in a transparent case.
- Client identifiers are removed.
- The stone is assigned a unique bar code that tracks it through every station.
- Weights and measures
- Carat weight is captured on an electronic micro‑balance to five decimal places.
- An optical device records measurements, facet angles, and proportions needed for downstream cut analysis.
- For round brilliants in the D to Z color range, these measurements help determine the overall Cut Grade.
- Color grading
- Performed in a standardized viewing environment with controlled light and neutral backgrounds.
- Multiple graders submit independent opinions without seeing one another’s entries.
- The final color grade is set when there is sufficient agreement.
- Clarity and finish
- Clarity is assessed under 10x magnification.
- A preliminary grader maps internal inclusions and surface blemishes, notes evidence of treatments, and records polish and symmetry.
- A second grader independently repeats the assessment. Senior gemologists review as needed until opinions converge.
- For round brilliants, polish and symmetry feed into the Cut Grade.
- Cut analysis for round brilliants
- Proportions, polish, symmetry, and observed optical performance are evaluated to assign a Cut Grade.
- Brightness, fire, scintillation, weight ratio, and durability are considered alongside craftsmanship.
- Quality assurance and routing
- Inventory Control randomly routes stones between graders.
- Each movement is tracked electronically so the lab can audit the entire path and every decision point.
The GIA grading scales you will see
Color scale, D to Z
- D to F: Colorless
- G to J: Near colorless
- K to M: Faint tint
- N to R: Very light tint
- S to Z: Light tint
Color is not a measure of brightness. It is a measure of body color when viewed in a controlled environment.
Clarity scale
- FL: Flawless
- IF: Internally Flawless
- VVS1, VVS2: Very Very Slightly Included
- VS1, VS2: Very Slightly Included
- SI1, SI2: Slightly Included
- I1, I2, I3: Included
Clarity grades are driven by the size, number, position, nature, and relief of inclusions at 10x magnification, along with their cumulative effect on appearance and durability.
Cut grade for standard round brilliants
- Excellent
- Very Good
- Good
- Fair
- Poor
Cut describes design and craftsmanship as expressed in face‑up performance. It is the single biggest driver of a diamond’s sparkle and life.
Additional descriptors that matter
- Polish: Quality of facet surface finishing, graded Excellent to Poor.
- Symmetry: Precision of facet alignment and balance, graded Excellent to Poor.
- Fluorescence: Diamond’s reaction to UV light, commonly None, Faint, Medium, Strong.
- Girdle inscription: Many stones are laser‑inscribed on the girdle with the GIA report number for secure identification.
- Proportions diagram: Shows table size, depth, crown and pavilion angles, and more.
- Plot: A diagram keyed to symbols that map notable clarity features.
How to read a GIA report in minutes
- Verify the report number and inscription match your diamond.
- Confirm basic data: shape, cutting style, measurements, carat weight.
- Review the 4Cs together. Do not over‑weight a single C in isolation.
- For round brilliants, make sure cut is at least Very Good, ideally Excellent.
- Look at polish and symmetry. Very Good or Excellent is the target.
- Check fluorescence. None or Faint is preferred for D to F color. None to Medium can be attractive for near‑colorless ranges.
- Review the plot and comments. Ask about phrases like “clarity grade based on clouds not shown,” internal laser drilling, or additional twinning wisps. These can affect transparency and brilliance and should be evaluated in person.
Report types you may encounter
- GIA Diamond Grading Report
Full grading for natural loose diamonds in the D to Z range. Includes plot, proportions, scales, and full 4Cs. - GIA Diamond Dossier
For smaller stones within a specified size range. Same core grading information but typically no inclusion plot. Dossiers are paired with a laser inscription.
Note: GIA continues to evolve report formats and delivery. Your House of Diamonds associate will explain current report options at the time of purchase.
Treatments and lab‑grown disclosures
- Diamond treatments such as laser drilling and HPHT color enhancement are noted in the report comments when detected.
- Natural and lab‑grown diamonds are graded in distinct report categories. Lab‑grown reports clearly disclose the origin. You will see this on the report header and in the inscription.
Practical buying guidance from our gemologists
- Prioritize cut first for round brilliants. Excellent cut with strong light return often outshines a larger but poorly cut stone.
- Balance color and clarity to your setting and preferences. Near‑colorless stones can appear very white in platinum or white gold.
- Inspect transparency. Two SI1 stones can look very different. Avoid stones where the clarity comment indicates clouds are the grade‑setting inclusion if the diamond appears milky in person.
- Read the proportions and look at the diamond in real lighting. Numbers inform, your eyes decide.
Why shop GIA‑graded diamonds with House of Diamonds AZ
- Selection curated by experts. We bring in diamonds that perform beautifully in person, not only on paper.
- Transparent education. We will walk you through the report and the diamond under magnification.
- Custom design in Arizona. Pair your diamond with a handmade setting created in our Scottsdale workshop.
- Local service and lifetime relationship. Cleanings, inspections, and support long after your purchase.
Visit us at 10323 N. Scottsdale Road, Scottsdale, AZ 85253. Call (602) 283‑5570 to schedule a private appointment.
Frequently asked questions
- Does GIA grade fancy shapes for cut?
GIA issues a formal Cut Grade only for standard round brilliants in the D to Z range. Fancy shapes receive detailed measurements, symmetry, and polish assessments, which we interpret for you. - Is fluorescence bad?
Not inherently. Faint to Medium fluorescence can be neutral or even helpful in some color ranges. Strong fluorescence can reduce value if it causes a hazy appearance. We evaluate this for you in natural light. - Can I trust a Dossier without a plot?
Yes. Dossier diamonds are laser‑inscribed with the report number, and you still receive full 4C grades, polish, symmetry, and comments. We show you the actual inclusions under the loupe or microscope. - What if a report comment mentions laser drilling or HPHT?
These are disclosures of treatments. We will advise you on how they impact value and appearance so you can make an informed choice.
