lecture 11: use of earth materials and energy from 6000-2000 years ago

porcellanite

a rare rock accounting for over half of the 16000 Irish stone axes examined by Mandal in 1997

when was porcellanite formed

60 million years ago

key developments in energy use c. 6000 BP

Boats and sailing boats (recorded pictorially in Kuwait) - revolutionised trade.

Domestication of oxen (Europe, Middle East) and water buffalo (India, SE Asia) as draft animals.

Invention of wooden scratch plough - more food.

Earliest potters' wheel, Sumeria - more and better pots

scratch ploughs - ard

Scratching furrows - ground preparation

Better germination, weeding, and prevention of seed eating

potter’s wheel

Turn wheel and table - transfer of momentum through spindle

key developments in material use 6000 BP

Lime mortar: first recorded as facing of Egyptian pyramids

Manufacture of arsenical copper in Greece: harder, more easily melted and cast, leading to better tools and weapons

But stone tools remain the norm: more widespread sources, easier to make, harder than all metals

breakthroughs in energy use by 5000 BP

Widespread use of charcoal to smelt copper in Balkans, Egypt and Sumeria by 5700 BP.

Wheeled vehicles date back to at least 5400 BP in Poland.

Domestication of horses ~5000 BP

use of lime cement in building

Temple-Palace, Mycenae Greece

Built around 3500 BP (Lee 1970)

glass

Smooth, hard but brittle; inert; can be produced in many colours.

Glass made by melting and controlled cooling of ingredients.

glass ingredients

• Pure quartz sand

• Natron (mainly sodium carbonate)

• Lime (calcium oxide)

Sometimes: 'vitreous materials'

later breakthroughs in glass technology

Moulded glass first developed in Middle east by 2500 BP

Clear, colourless glass eventually perfected by 2300 BP in Mesopotamia and Turkey.

alloys and bronze

An alloy is an atomic scale solid mixture of metals.

Up to ~14% tin can be added to copper without major change to atomic structure.

Tin atoms larger than copper atoms: bronze alloys harder than pure copper.

early bronze

Bronze = alloy of ~88% Cu and ~12% tin

Harder than copper; harder than arsenical Cu: better tools and non-toxic

Smelting temperature copper 1084 degrees C, with tin 950 degrees C.

Charcoal required for smelting Cu and tin ores to make bronze.

Oldest known artefacts ~4500 BP in Sumeria, less made ~4000 BP

discovery of tin

Tin unknown as metal when first used to make bronze

Tin ore, called cassiterite (SnO2), much less common than copper ore and more difficult to recognise

Sumerians’ local tin ore supply used up by 4,000 BP?

Tin not smelted alone until 4,000 BP

Irish bronze age copper mines

Expansion of Bronze Age sites in Ireland c. 2500 cal BC–1900 cal BC).

Coastal exposures of malachite in west Cork and Waterford probably first to be mined for copper

But no evidence, probably due to subsequent coastal erosion

ross island, Killarney

Bronze age copper mining, 4400-3800 BP

Mount Gabriel, Cork

Exploited after Ross Island, around 3,500 BP

• Lower grade ores

• Copper in malachite, not in sulphides as at Ross Island

• Less accessible

iron

Compared to bronze: harder; commoner ores

Earliest known smelting ~4,000 BP in Anatolia, widespread in Middle East 3,200 BP

Iron spread through Europe, reaching Ireland by 2,500 BP

smelting iron and the iron age

Iron itself not melted, must be physically removed from slag, then worked to make wrought iron

bloomery furnace

iron oxide ore heated in charcoal fire to remove oxygen