The Gold Karat Purity Spectrum and Hallmark Standards
The word Karat (spelled with a 'K' for gold fineness, as distinguished from 'Carat' with a 'C' for gemstone weight) denotes purity based on 24 fractional parts. If a metal alloy is 24 Karat, all 24 parts are pure elemental gold. If it is 18 Karat, exactly 18 parts are gold and 6 parts are alloying metals:
| Karat Grade | Purity Ratio | Hallmark Stamp | Fine Gold Content | Alloy Proportion | Primary Jewelry Usage in BD |
|---|---|---|---|---|---|
| 24 Karat | 24 ÷ 24 | 999 Hallmark | 99.90% | 0.10% Trace | Investment bullion bars, minted coins, raw casting grain |
| 22 Karat | 22 ÷ 24 | 916 Hallmark | 91.67% | 8.33% Copper & Silver | Bridal necklaces, wedding bangles, heavy gold sets |
| 21 Karat | 21 ÷ 24 | 875 Hallmark | 87.50% | 12.50% Copper & Silver | Daily wear jewelry, Middle East imports, chains, rings |
| 18 Karat | 18 ÷ 24 | 750 Hallmark | 75.00% | 25.00% Base Alloys | Diamond jewelry settings, white gold, contemporary pieces |
| 14 Karat | 14 ÷ 24 | 585 Hallmark | 58.33% | 41.67% Base Alloys | Western lightweight imports, durable sport rings |
| Sanatan (Traditional) | Varies | Non-hallmarked | 50% to 70% | Variable Solder Mix | Antique family heirlooms, vintage handcrafted items |
Mode 1: Decomposing Fine Gold vs Base Alloy Weight
When assessing jewelry value or calculating raw metal buy-backs, you must separate the pure gold weight from base alloy weight:
Example: In 10 grams of 22K gold, the fine bullion content is 10 × (22 ÷ 24) = 9.167 grams.
Example: In 10 grams of 22K gold, the alloy content is 10 × (2 ÷ 24) = 0.833 grams.
Mode 2: Karat Alteration (Adding Alloy or Bullion)
Professional goldsmiths in workshops across Tanti Bazar and Baitul Mukarram frequently need to alter the karat grade of existing metal stocks:
To convert higher-karat gold into a lower karat (for example, blending pure 24K bullion down to 22K or 18K), use this formula:
Example: Lowering 11.664g (1 Vori) of 24K down to 22K requires adding 11.664 × [(24 ÷ 22) - 1] = 11.664 × 0.0909 = 1.060 grams of alloy metal.
To upgrade lower-karat scrap into a higher karat (for example, elevating 18K gold to 21K or 22K), use this formula:
Example: Raising 10 grams of 18K gold up to 22K requires adding 10 × [(22 - 18) ÷ (24 - 22)] = 10 × (4 ÷ 2) = 20.0 grams of 24K pure bullion.
Metallurgical Recipes for Colored Gold Alloys
The specific metals chosen for the alloy portion determine the color, ductility, and hardness of the finished jewelry:
Balanced blend of 50% Copper and 50% Silver. Retains warm natural golden luster while providing excellent tensile strength for stone prong settings.
Rich in Copper (approximately 75% Copper and 25% Silver). The high copper content imparts an elegant reddish-pink hue popular in modern engagement bands.
Alloyed with Palladium, Silver, Zinc, or Nickel. Rhodium plating is applied electrochemically to provide a mirror-bright silvery finish for diamond solitaires.
How to Use This Karat Converter Terminal
Choose Purity Breakdown mode to isolate fine gold vs alloy, or Karat Alteration mode to formulate alloy recipes.
Enter total weight in traditional Vori, Ana, Roti, and Points, or switch to decimal Grams seamlessly.
Select standard grades (24K, 22K, 21K, 18K) or input custom millesimal fineness numbers directly.
Inspect itemized pure gold weight, required additive metal mass, and total market valuation in BDT.
Explore Related Bullion Calculators & Converters
Supplement your metallurgical conversions with our suite of specialized precious metal calculators:
Karat purity ratios, hallmark fineness classifications, and alloy formulation formulas comply with technical guidelines set by the Bangladesh Jewellers Association (BAJUS) and international assaying standards. Curated and reviewed by Senior Bullion Analyst Mehedi Hasan.
