How to Appraise Diamonds for Buying and Reselling at the Right Value

The 4C standard of diamonds is a global diamond grading system that includes Carat (weight), Cut, Color, and Clarity. This is a grading system developed by the Gemological Institute of America (GIA) and widely recognized around the world, considered the common language of the jewelry industry, helping buyers and experts worldwide understand and compare diamond quality accurately and transparently.

Thanks to the 4C standard, buyers can clearly understand the true value of the diamond they own, as brands and grading centers have a basis to verify, certify, and value diamonds consistently worldwide.

Carat is the first parameter and the foundation for price lookup. It determines the weight of the diamond, thereby establishing the initial base price (Price / Carat).

1 Carat equals 6.5 ly

A difference of just 0.01 carat can also change the value of a diamond; a 0.99 ct diamond is worth significantly less than a 1.00 ct diamond, even though their size appears almost identical to the naked eye, yet it can create a difference of millions of VND.

This shows the importance of precision in measuring weight, because even a small discrepancy directly affects valuation and transparency in transactions.

Cut is the only factor influenced by humans and is the factor that most strongly affects sparkle and overall beauty (fire, brightness). A perfect cut ensures optimal light reflection.

Cut is considered the most important final price-adjusting factor. A diamond with high 3Cs (Carat, Color, Clarity) but poor Cut will have much lower value.

Diamonds graded Excellent or Triple Excellent (3EX) always have the highest price in the same remaining 3Cs segment, because they reflect fine craftsmanship and optimized beauty.

Diamond cut is divided into 5 grades

Clarity

Diamond clarity evaluates cleanliness based on the number, size, and position of inclusions and blemishes under 10x magnification.

Impact on price:

• Perfect clarity grades (FL – Flawless and IF – Internally Flawless) have the highest value due to their rarity.
• Most buyers choose VS or VVS grades because they have no inclusions visible to the naked eye, offering good value.
• Diamonds with inclusions visible to the naked eye (I1, I2, I3) have the lowest value.

• Colorless diamonds (Colorless: D-F) have the highest value.
• Diamonds with a slight yellow/brown tint (Near Colorless: G-J and lower) are priced significantly lower. Choosing a slightly lower color grade (for example, from D down to G) is the most effective way to reduce cost while making the difference hard to notice with the naked eye.

GIA (Gemological Institute of America) is the world’s most reputable and authoritative diamond grading organization. A GIA certificate provides an objective and standardized report on the diamond’s 4Cs. The presence of a GIA certificate ensures authenticity, transparency, and serves as solid proof of quality. 

GIA certificate

Diamonds with GIA certificates are often priced higher than those without certificates or with certificates from less reputable laboratories. To ensure they are not swapped, the number on the GIA certificate is usually micro-engraved (not visible to the naked eye) on the girdle of the diamond.

It is the phenomenon in which a diamond emits light (usually blue) when exposed to ultraviolet (UV) rays. GIA classifies it from None to Very Strong. 

According to GIA, Fluorescence is divided into 5 levels: None - Faint - Medium - Strong - Very Strong

Weak fluorescence can enhance brightness, but if too strong, the stone may appear hazy or milky, reducing its value.

• D, E, F color diamonds with weaker fluorescence have higher value
• I, J, K – Z color diamonds with stronger fluorescence have higher value

Shape is the external form of the diamond (for example: Round, Oval, Princess), while Cut is the quality of the facets.

Round Brilliant diamonds are the most popular shape and have the highest price because they require complex cutting techniques and waste the most rough material. Fancy shapes (Oval, Princess, etc.) are usually more affordable.

The external shape of a diamond

Diamond valuation in the market is based on a Pricing Grid, most commonly the Rapaport price list. This is an international standard system used to determine the unit price per carat based on Carat – Color – Clarity.

The pricing process is carried out in two steps:

Step 1: Calculate the wholesale price according to the price list

The wholesale price is calculated by multiplying the carat weight by the price per carat.

Formula:

Wholesale price = Carat weight × Price Per Carat

Step 2: Adjust the price according to Cut and market factors

After obtaining the wholesale price, the retail price is adjusted by cut quality and other commercial factors.

Formula:

Retail price = Wholesale price × Cut factor × Market Markup

Note: Cut is not a factor used to look up the price list, but it is a factor that strongly affects the final price.

Jemmia Diamond: A reputable, quality place to buy diamonds

When investing in diamonds, choosing a reputable brand is a key factor. Jemmia Diamond is a typical example and is proud to be a company authorized by the Gemological Institute of America (GIA) to import and distribute authentic GIA-certified diamonds in Vietnam. Jemmia meets and exceeds strict international standards:

• Legal compliance & transparency: Diamonds are 100% officially imported through customs, ensuring full sales invoices and GIA documentation, helping customers feel secure in owning legal assets.
• Selected quality: Only the top 2% most beautiful diamonds in the world are selected through a rigorous inspection process according to GIA’s 4Cs standards, with a commitment not to use diamonds with flaws that affect durability and structure.
• Modern technology: A pioneer in using 100% technology equipment imported from GIA USA (including GIA iD100, GIA Diamond Dock, GIA Match iD…) to verify quality and origin, ensuring absolute accuracy.
• Ethical diamonds: Committed to importing only from countries that comply with the "Kimberley Process," ensuring diamonds are not mined from war zones.
• Pricing & trade-in policy: Diamond price lists are public and transparent, along with the best buyback and trade-in policy on the market, helping customers invest with confidence and easily upgrade products in the future.