The purity or fineness of silver alloys is now described using the millesimal system in most countries. This system uses a number to represent the purity of the alloy. The number described purity in parts per thousand.

Previous to the millesimal system, the fineness of silver was expressed in carats. While the fineness of silver alloys must be stamped or hallmarked into pieces, the millesimal value is generally compulsory and the carat value now optional.

Table 1. Some of the most common fineness denominations used.

Fineness	Common Name	Purity (wt.%)
999	Fine or pure silver	99.9
958	Brittania	95.8
925	Sterling silver	92.5
800	Jewellery silver	80

Pure silver is typically very soft and malleable, hence it is commonly alloyed to increase its hardness and durability for applications such as jewellery. It is typically alloyed with copper in this instance, with sterling silver being one of the most popular alloys, containing 7.5% copper. Copper is used as it is a hardening agent and does not discolour the silver.

This metal has been known since prehistoric times. Gold is a soft metal with a characteristic yellow colour. It is the most malleable and ductile of any element. It is unaffected by air, water, alkalis and acids, with the exception of “aqua regia”, HNO3/HCl. The fact that it is chemically unreactive means that it is often found in its natural state. It is a good thermal and electrical conductor and has excellent reflective properties to both light and infrared. It has an abundance in the earth’s crust of 0.0011 ppm. Most of the metal is retained for use as bullion reserves, but some is used within the electronics and jewellery industries, where it is frequently alloyed with other elements to improve the mechanical properties of the metal (e.g. copper and silver). Other uses for the metal are as a heat reflecting coating for glass as well as as a decorative medium.

Key Properties

Atomic Properties Atomic number 79 Atomic radius - Goldschmidt ( nm ) 0.144 Atomic weight ( amu ) 196.9665 Crystal structure Face centred cubic Electronic structure Xe 4f14 5d10 6s1 Photo-electric work function ( eV ) 4.8 Thermal neutron absorption cross-section ( Barns ) 98.8 Valences shown 1,3 Ionisation Potential No. eV 1 9.22 2 20.5 Natural Isotope Distribution Mass No. % 197 100 Electrical Properties Temperature coefficient ( K-1 ) 0.0040 @ 0-100 Electrical resistivity ( µOhm.cm ) 2.20 @ 20 Thermal emf against Pt (cold 0°C - hot 100°C) ( mV ) +0.74 Mechanical Properties Material condition Soft Hard Polycrystalline Bulk modulus ( GPa ) 171 Hardness - Vickers 20-30 60 Poisson's ratio 0.42 Tensile modulus ( GPa ) 78.5 Tensile strength ( MPa ) 130 220 Yield strength ( MPa ) 205 Physical Properties Boiling point (°C ) 3080 Density ( g.cm-3 ) 19.30 @ 20 Melting point (°C ) 1064.4 Thermal Properties Coefficient of thermal expansion ( x10-6 K-1 ) 14.1 @ 0-100 Latent heat of evaporation ( J.g-1 ) 1738 Latent heat of fusion ( J.g-1 ) 64.9 Specific heat ( J.K-1.kg-1 ) 129 @ 25 Thermal conductivity ( W.m-1.K-1 ) 318 @ 0-100

Platinum is a transition metal element. Mostly noted as a precious metal used in jewellery, its extremely low reactivity and thermal stability see it used in laboratory ware.

Properties

Property		Value
Atomic Number		78
Atomic Mass		195.09
Density		21.09g/cm3
Melting Point		1768˚C
Boiling Point		3825˚C
CAS Number		7440-06-4

Available Sizes

· 25x25mm

· 50x50mm

· 75x75mm

· 100x100mm

Open area: 62.7%; Width of opening: 0.015in

Platinum is a transition metal element. Mostly noted as a precious metal used in jewellery, its extremely low reactivity and thermal stability see it used in laboratory ware.

Properties

Property		Value
Atomic Number		78
Atomic Mass		195.09
Density		21.09g/cm3
Melting Point		1768˚C
Boiling Point		3825˚C
CAS Number		7440-06-4

Available Sizes

· 5cm

· 25cm

· 100cm

Approximately 16.8g/m

Dosilac is a new conductive silver spray paint from Ami Doduco. It combines speed, ease and economy for the application of metal coatings to non-conducting surfaces.

The purpose designed nozzle makes dosing easy and gives a uniform coating.

Spraying is economical compared to brushing as it is able to cover ten times the surface area with the same amount of material. Furthermore, the paint does not dry in the can meaning that there are lower losses and the material remains more consistent.

The silver spray paint provides a better alternative to traditional silver conductive paints that require application by brush. They are suited to applications including, but certainly not limited to:

· Dentistry

· Jewellery

· Amateur electronics

· Repairing printed circuit boards

· Electromagnetic shielding

· Rear windscreen heaters