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 gives the proton count of an element in the periodic table, while the atomic weight (relative atomic mass) describes the average mass of its atoms in atomic mass units.

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

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

Density expresses how much mass a substance packs into a given volume, and for precious metals it serves as a central marker of authenticity.

Diamagnetism is the faint pushing-away of a material by an external magnetic field; because gold is diamagnetic, magnets do not attract it.

Ductility denotes 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 enthalpy of fusion is the amount of energy a substance must absorb in order to change from the solid to the liquid state at its melting point, without changing its temperature.

The melting point is the temperature at which a substance changes from the solid to the liquid state under normal pressure, without the temperature changing during melting.

Mohs hardness is a dimensionless index on a scale from 1 to 10 that describes the resistance of a mineral to being scratched by a harder material.

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

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

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

Tarnishing is 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 heat energy through itself and is expressed in watts per metre and kelvin (W/(m·K)).