Physics & Chemistry

Aqua regia is a highly oxidising acid mixture of concentrated hydrochloric and nitric acid (3:1) and is the only liquid reagent capable of dissolving the noble 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 a vehicle exhaust-treatment system that uses platinum-group metals (platinum, palladium, rhodium) to turn harmful combustion residues into non-toxic compounds.

Corrosion resistance is the ability of a material to withstand chemical attack from moisture, oxygen, acids or other environmental influences over time without significant change to its surface or structure.

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

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

Ductility is the ability of a material to deform plastically under tensile stress without fracturing.

Electrical conductivity describes how well a material carries an electric current and, for precious metals, is a key quality criterion in industrial applications.

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

The melting point is the temperature at which a substance changes from solid to liquid at normal pressure, with the temperature staying constant throughout the melting process.

A unitless rating from 1 to 10 that captures how well a mineral withstands being scratched by something harder than itself.

A metal counts as precious when its standard electrode potential is markedly more positive than that of the hydrogen electrode, so that under normal conditions it does not react with water, oxygen or most acids.

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

Specific gravity (also called relative density) expresses how much heavier a substance is compared with water (density 1.0 g/cm³), and it ranks among the most reliable figures for verifying the authenticity of precious metals.

Tarnishing is the surface discolouration of metals caused by a chemical reaction with sulphur compounds or oxygen in the surrounding air.

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