Melting Point

The melting point (also melting temperature) describes a fundamental change of state in 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 heat of fusion, not into further heating. This makes the melting point a substance-specific and highly precise characteristic value of central importance in analysis, metallurgy and precious metal processing.

Physical Background

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

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 values 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 direct implications for melting, alloying and processing:

The low melting point of silver compared to platinum explains why silversmiths since antiquity could manage with simpler furnaces, whereas the processing of platinum-group metals only became possible with modern high-temperature furnaces and electric arcs.

Significance for Alloys

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

For precious metal alloys:

• 585 gold (14 karat): contains silver and copper alongside gold; the melting range, depending on the alloy, lies at approximately 880–950 °C — well below gold's melting point.
• 750 gold (18 karat): melting range typically 880–960 °C.
• White gold with palladium: the addition of palladium raises the melting point (to 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 fineness — regardless of the specific melting point of the alloy.

Relevance for Authenticity Testing

The melting point is an indirect security feature: tungsten forgeries of gold bars are theoretically unmasked by tungsten's high melting point (3,422 °C), since tungsten remains solid at gold's melting temperature. In practice, however, this is detected more readily by density determination, X-ray fluorescence analysis or ultrasound testing, as a genuine melt test would destroy the bar.

For everyday testing, non-destructive methods are recommended; the coin weight checker helps verify coins for authenticity based on weight and dimensions.

Melting Point and Recycling

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

• Greater energy input for melting
• Specialist alloys required for crucibles and moulds (e.g. graphite, ceramics)
• Longer cooling times

Gold and silver can be recycled particularly economically thanks to their comparatively low melting points — a factor that favours precious metal recycling compared to industrial metals with very high melting points.

In Brief

The melting point is one of the most precise physical characteristics 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 shifts to 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 design to forgery detection.