Physics & Chemistry

Aqua regia is a strongly oxidising acid mixture of concentrated hydrochloric acid and nitric acid (3:1) that is the only liquid reagent capable of dissolving the precious metals gold and platinum.

The atomic number indicates the number of protons of an element in the periodic table; the atomic weight (relative atomic mass) describes the average mass of its atoms in atomic mass units.

A catalytic converter is an exhaust emission control system in a vehicle that uses platinum group metals (platinum, palladium, rhodium) to convert harmful combustion by-products into non-toxic compounds.

Corrosion resistance describes the ability of a material to permanently withstand chemical attack by moisture, oxygen, acids, or other environmental influences without significantly altering its surface or structure.

The density of a substance indicates how much mass is contained per unit of volume, and is a key authenticity characteristic for precious metals.

Diamagnetism describes the weak repulsion of a material by an external magnetic field; gold is diamagnetic and is therefore not attracted by magnets.

Ductility describes the property of a material to deform plastically under tensile load without breaking.

Electrical conductivity describes how well a material conducts electric current, and is an important quality characteristic of precious metals for industrial applications.

The heat of fusion is the amount of energy a substance must absorb at its melting point to transition from the solid to the liquid state without any change in temperature.

The melting point is the temperature at which a substance transitions from the solid to the liquid state at standard pressure, without any change in temperature during the melting process.

The Mohs hardness is a dimensionless value on a scale of 1 to 10 that describes the resistance of a mineral to scratching by a harder material.

Precious metals are defined as metals with a standard electrode potential that is significantly more positive than that of the hydrogen electrode, meaning they do not react with water, oxygen or most acids under standard conditions.

The reflectivity (reflectance) of a metal indicates what proportion of incident light its surface reflects back, and is responsible for the characteristic metallic lustre of gold, silver, and other precious metals.

Specific gravity (also: relative density) indicates how much heavier a substance is compared to water (density 1.0 g/cm³) and is one of the most reliable indicators for verifying the authenticity of precious metals.

Tarnishing refers to the surface discolouration of metals caused by a chemical reaction with sulphur compounds or oxygen from the surrounding air.

Thermal conductivity describes how well a material transports thermal energy through itself and is expressed in watts per metre per kelvin (W/(m·K)).