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Carat Fineness Precious Metals

Reference data and engineering information about carat fineness precious metals for material properties applications.

caratfinenesspreciousmetals

Overview

Engineering reference data for Carat Fineness Precious Metals in material science and properties.

Key Formulas

Stress

σ=FA\sigma = \frac{F}{A}

Force per unit area.

Strain

ε=ΔLL0\varepsilon = \frac{\Delta L}{L_0}

Change in length per original length.

Hooke's Law

σ=Eε\sigma = E \varepsilon

Stress proportional to strain in elastic region.

Thermal Expansion

ΔL=αL0ΔT\Delta L = \alpha L_0 \Delta T

Length change due to temperature.

Variables

Symbol Description Unit
σ\sigma Stress Pa
ε\varepsilon Strain —
EE Young's modulus Pa
α\alpha Thermal expansion coefficient 1/°C
ΔT\Delta T Temperature change °C

Definitions

Fineness is the proportion of pure precious metal in an alloy, expressed in parts per thousand (‰, also written as "o/oo"). Karat (K or kt) is a unit of measurement for the purity of gold alloys, where pure gold is defined as 24 karat.

Karat and Fineness Formula

The purity of gold can be calculated from its karat rating using the following formula:

Fineness (decimal)=Karat24\text{Fineness (decimal)} = \frac{\text{Karat}}{24}

To express this as a percentage or in parts per thousand (‰), the conversion is:

Fineness (%)=(Karat24)×100\text{Fineness (\%)} = \left( \frac{\text{Karat}}{24} \right) \times 100 Fineness (‰)=(Karat24)×1000\text{Fineness (‰)} = \left( \frac{\text{Karat}}{24} \right) \times 1000

Gold Alloy Properties and Common Karat Ratings

The following table summarizes common karat ratings, their equivalent fineness, and their typical suitability for jewelry applications. Pure gold (24 K) is very soft and is almost always alloyed with other metals like silver, copper, nickel, or zinc to improve its strength and durability.

Karat (K) Fineness (decimal) Fineness (%) Fineness (‰) Suitability for Jewelry
*24 1.000 100% 1000.00 Very soft; not recommended.
*22 0.917 91.7% 916.67 Soft; not recommended.
*18 0.750 75.0% 750.00 Recommended for fine jewelry.
*14 0.583 58.3% 583.33 Common for average jewelry.
*12 0.500 50.0% 500.00 Not acceptable in jewelry.
*10 0.417 41.7% 416.67 Minimum for "real" gold.
*8 0.333 33.3% 333.33 Low purity.

Permille Notation in Gold Fineness

Gold fineness is often expressed in parts per thousand (permille), denoted as o/oo. The conversion from karat to permille is given by:

Permille=(Karat24)×1000\text{Permille} = \left( \frac{\text{Karat}}{24} \right) \times 1000

Below is a reference table for common karat values and their equivalents in fraction, percentage, and permille:

References