Award Winning Bronze, Silver & Fine Art Foundry

A Brief History of Bronze

A Brief History of Bronze

There are three accepted phases within the bronze age - early (2400-1600BC); middle (1600-1200BC; and, late (1200-600BC). Each is defined to an extent by the step changes in metal technology.

Thousands of copper, bronze and gold artefacts have been discovered by archeologists and serve to document the developments of this period.

Increasing organization of agriculture, the use of fire and the invention of the wheel all in their own ways supported the development from stone tools to copper tools and decorations. Our Bronze Age ancestors were far from primitive in their habits. As well as day-to-day practical tools they had tweezers, double-edged blades that could have been razors and other items which suggest a care about appearance.

Moulded Axes

Once metal-working skills were developed, crafts-people were soon producing bronze and gold pieces which even modern metal workers admire and envy. Axe heads have been found that were clearly moulded in a carved stone mould and stone moulds themselves have been uncovered.

The first metal-workers would probably have used copper which while it is maleable (it can be shaped by hammering) is soft. Copper itself cannot be cast in moulds very well. However, each source of copper came with its own impurities depending on the other metal ores mined with it. Early alloys would have been 'accidental' - the addition of other metals being in the form of these natural impurities. Iron, arsenic, antimony, lead, nickle and bismuth were all often found in early copper in varying degrees and proportions.

Poisonous Alloys

Copper containing arsenic, while harder than pure copper, would have produced gaseous arsenic compunds during smelting - this would have been seriously injurious to health and almsot certainly will have contributed to deaths of those working with it. Lead in reasonable quantities produces a softer alloy, whereas bismuth even in minute quantities produces a brittle copper alloy.

The first intentional alloy of copper was the copper-tin alloy. This is bronze. This alloy is harder than copper and less brittle than other alloys. Both metals were widely available and with the influence of the Phoenicians, bronze alloys were created more scientifically and consistently throughout Europe. Phoenician bronze was usually 10 per cent tin and 90 per cent copper.

Modern bronzes vary in the proportions of the constituent metals: 3 per cent tin is a 'mild' bronze, 25 per cent tin produces the harder ringing metal used for bells.

All copper-tin alloys with more than 78 per cent copper are called bronzes. Other metals can be added to determine the final characteristics of the metal - phosphor bronze, for example, contains a small proportion of phosphorus and is very hard, weather and shock-resistant.

It seems strange that combining two, three or even four inherently soft metals in the correct proportions can produce some of the hardest wearing and most beautiful metal alloys.

Practical to aesthetic

In modern times, the price of copper and tin is so high that bronze is used less for practical purposes than it is for artistic and architectural purposes. Although, there are a few engineering applications for which only specific grades of bronze are suitable.

Although founders still use a wide range of alloys depending on the application, modern casting teachniques allow the use of a more modern blend: an alloy of copper and silicon with carefully controlled trace amounts of other metals such as manganese and zinc. This alloy is especially suited to the ceramic shell casting technique. The molten copper-silicon alloy flows very freely allowing great details to be achieved in the finished bronze.

Patination

Bronze in its natural polished state is indistinguishable, to the eye, from brass - a golden yellow. However if left in the open in a relatively damp environment it develops a distinctive 'patina' or coating in shades of green - this is the copper oxide verdigris (literally: green-grey) coating which develops on exposure to the air. This coating is not only of great character but protects the remaining metal from further corrosion. Never polish a bronze piece if it is kept outside - you will be wearing away the coating and gradually the detail on the piece will erode.

Dinsdale Petch - Pouring the bronze