Melting Point

The melting point (also melting temperature) describes a fundamental change of state of matter: when a crystalline solid is heated to this characteristic temperature, the ordered lattice collapses and the substance becomes liquid. Throughout the entire melting process the temperature remains constant – the supplied energy flows exclusively into the so-called enthalpy of fusion, not into further heating. This makes the melting point a substance-specific and highly precise metric with central importance in analytics, metallurgy and precious metal processing.

Physical background

The melting point is the equilibrium point of two phases: solid and liquid coexist as long as heat is supplied. For pure, crystalline substances it is sharply defined; alloys, by contrast, melt over a range (solidus to liquidus temperature) because the components bring different lattice bonds.

Melting process (pure substance):
────────────────────────────────────────────────────
Temperature ▲
            │            ●●●●●●●● (liquid)
            │           ●
Melting     │──────────●────────────── T_m (constant)
point T_m   │        ●
            │      ●● (solid + liquid simultaneously)
            │    ●●
            └──────────────────────────────────► Time
          Heat input →
────────────────────────────────────────────────────

The melting point is pressure-dependent: increased pressure shifts it slightly upward for most metals. Standard figures always refer to standard pressure (1,013.25 hPa).

Melting points of precious metals compared

The melting points of the most important precious metals and related metals differ considerably and have a direct impact on melting, alloying and processing operations:

The low melting point of silver compared to platinum explains why silversmiths managed with simpler furnaces since antiquity, whereas processing platinum metals only became possible with modern high-temperature furnaces and arc melting.

Significance for alloys

When two or more metals are melted together, an alloy is created whose melting point differs from that of the individual components. Particularly important here is the eutectic mixture: the composition at which the melting point minimum of a multi-component system is reached.

For precious metal alloys the following applies:

• 585 gold (14 carat): in addition to gold it typically contains silver and copper; the melting range lies, depending on the alloy, at roughly 880–950 °C – clearly below the gold melting point.
• 750 gold (18 carat): melting range usually 880–960 °C.
• White gold with palladium: the palladium addition raises the melting point (up to 1,100–1,200 °C).
• Sterling silver (925): melting point approx. 893 °C (compared to 961.8 °C for fine silver).

This behaviour is practically relevant for goldsmiths, refineries and recycling operations: the Melt Value Calculator determines the material value on the basis of the fineness – regardless of the specific melting point of the alloy.

Relevance for authenticity testing

The melting point is an indirect security feature: tungsten counterfeits of gold bars are, in theory, exposed by tungsten's high melting point (3,422 °C), since tungsten remains solid at the melting temperature of gold. In practice, however, this is detected rather by density measurement, X-ray fluorescence analysis or ultrasonic testing, because an actual melt test would destroy the bar.

For everyday testing, non-destructive methods are recommended; the Coin Weight Checker helps verify coins for authenticity using weight and dimensions.

Melting point and recycling

In precious metal affinage and in the recycling of broken gold, dental gold and old jewellery, the melting point plays an important role in process planning. Higher melting temperatures mean:

• Higher energy input during melting
• Special alloys for crucibles and moulds required (e.g. graphite, ceramic)
• Longer cooling times

Gold and silver can be recycled particularly economically because of their comparatively low melting points – a factor that favours the recycling of precious metals over industrial metals with very high melting points.

In brief

The melting point is one of the most precise physical properties of a metal: for precious metals it lies between roughly 962 °C (silver) and almost 2,000 °C (rhodium), remains exactly constant for pure metals, and turns into a melting range for alloys. For practice in goldsmithing, refining and precious metal testing it is indispensable basic knowledge – from the Melt Value Calculator through alloy planning to counterfeit detection.