A to Z

De-mystifying the terms used by antique dealers, auctioneers and specialists.
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Term Main definition
Aluminium Bronze

Copper-aluminium alloys with up to 13% of aluminium, usually also with other additions such as iron, manganese, nickel and/or silicon. These alloys are strong, hard and have excellent resistance to marine corrosion. They are therefore commonly used for making propellers, bearings, gears, valves, and pipe fittings for seawater use.

Aluminium Brass

High copper brass with aluminium added for improved corrosion resistance. This is often used for condenser tubes.


Al - Chemical symbol for Aluminium.

Element with atomic weight 26.98, atomic number 13, mp 660.37 ºC, specific gravity 2.69. It is the most abundant of the metallic elements but is very difficult to extract and was not properly known until 1827. 

Aluminium is an easy metal to polish. It is soft enough that even the roughest aluminium parts can be quickly polished to a bright shine.

Polished aluminium has a fault, it tarnishes quickly. Most factory polished aluminium parts are sprayed with a clear lacquer, acrylic or urethane to seal the part.

Like stainless steel, aluminium is relatively resistant to corrosion, but it is very susceptible to attack by strong acids and alkalis used in some cleaning products.

Alumina Silicate Glass

A special glass used for glass-to-metal seals, particularly suitable when operating temperatures of electrical components are high (up to 750°C). Alumina (aluminium oxide Al2O3) is added to the glass batch in the form of commonly found feldspars containing alkalis in order to help improve chemical resistance and mechanical strength, and to increase viscosity at lower temperatures.


Generic term for Nickel silver, also argentan.

Alpha Delta Eutectoid (in bronze)
A hard constituent normally present in the structure of cast bronze containing more than about 6% tin. (Delta phase intermetallic composition, Cu31Sn8).
Alpha Brass

An alloy of copper and zinc with no more than 38% zinc so that the beta phase is not formed. In antiquity, the cementation process for the manufacture of brass meant that only up to 28% zinc might be absorbed in the copper when the zinc ore was reduced in situ. Most ancient brasses do not contain over 28% zinc. 

Alpha Beta Brass
Brass containing over 36% of zinc or with other additions usually has two phases present in the crystal structure, alpha and beta. They are used for castings, extrusions and for hot stampings. A brass with sufficient zinc present to allow the development of the beta phase. The equilibrium range of the alpha-beta composition varies with temperature being 33.5 to 36.8% at the solidus temperature, and 35 to 46.6 % at room temperature. As the beta to alpha reaction is a diffusion controlled reaction, it is relatively slow, thus it is possible to control the relative proportion of alpha to beta phases by a combination of composition and heat treatment so that the combination of tensile strength to ductility can be optimised. 
Brass with the addition of nickel, that has a strong bleaching property, and is extremely easy to work and resistant to corrosion. It is known under such names as Alpaca, Alpacca, Albata, Argentan, Baitong, German Silver, Maillechort, New Silver, Nickel Brass, Nickel Silver, Pakfong, Paktong, etc. and is an alloy consisting of mostly copper and other metals as follows:

Copper 55% approx.

Nickel 20% approx.
Zinc 20% approx.
Tin 05% approx. 
Alpakka is a very durable metal that can be polished to a high lustre shine. Acid will attack and dissolve the zinc causing pitting corrosion, so avoid contact with citric fruits and products containing acid.
Alluvial Deposit
The local concentration of minerals in old river and stream deposits (Alluvium). These form when minerals weathered and transported from the original solid geology deposits are locally concentrated in the bed of the stream. These stream deposits may be buried to some considerable depth below subsequent quaternary gravels. Tin and gold in particular are concentrated in such deposits. Much of the medieval and earlier tin mined in Devon and Cornwall came from stream works working this type of deposit. 

A metallic mixture two or more elements. An alloy can be formed from a mixture of two or more metals e.g. copper and tin to form bronze, or by a mixture of a metallic and non-metallic element e.g. iron and carbon to form steel, or cast iron. 

It has been suggested that the term alloy should only be used when there is a suggestion that the mixing was deliberate. In the study of ancient metallurgy it is difficult to prove deliberate mixing in some cases, e.g. when the ‘alloy’ could have arisen by co-smelting e.g. Cu-As and Fe-C-P 1 alloys. So, an alternative use of the term would be - any metallic mixture of elements whose physical, mechanical, or metallurgical properties differed substantially from the constituent elements. 

In silver, the base metals are added for strength.

Allotropes of Iron

Iron as a solid exists in different allotropic crystalline forms. The most important are alpha iron (ferrite) and gamma iron (austenite). The crystal lattice arrangement of alpha iron is one which is body centred whereas that of gamma iron is a face-centred cubic arrangement. The iron-carbon equilibrium diagram (technically the iron-iron carbide meta-stable phase diagram) shows the temperature ranges in which each form of iron is most stable as well as the carbon solubility range for these allotropes or phases. 

The great importance of the two crystalline forms of iron lies in the difference of the solubility in solid solution of carbon between the two. Carbon is virtually insoluble in the body-centred ferrite form, the lattice structure of which will only accept a maximum of 0.04% of carbon. The face-centred cubic lattice of austenite will accept carbon atoms more readily and up to about 2.1% carbon is soluble in alpha iron. 


Certain substances can exist in more than one crystalline form; for example carbon can be found as graphite, diamond, or the recently discovered buckminster-fullerene. Pure iron has three main allotropes alpha (ferrite) , and gamma (austenite) and delta, which are stable at different temperatures. 

All Wood Furniture
Constructed of wooden components; includes solids, veneered and engineered woods.
Alkali-Borosilicate Glass
A special glass used for glass-to-metal seals, particularly suitable when electrical qualities are not important.