Physics & Chemistry

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

The atomic number states the number of protons 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-cleaning system 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 withstand chemical attack from moisture, oxygen, acids or other environmental influences permanently, 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 central authenticity feature 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 refers to a material's ability to deform plastically under tensile stress without breaking.

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

The enthalpy of fusion is the amount of energy a substance must absorb 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 standard pressure, without its temperature changing during melting.

Mohs hardness is a dimensionless figure on a scale from 1 to 10 that describes a mineral's resistance 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, which means they do not react with water, oxygen or most acids under normal conditions.

The reflectivity (reflectance) 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 testing the authenticity of precious metals.

Tarnishing refers to the surface discolouration of metals through 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)).