Class Notes on Early Metallurgy

 "The appearance of metals in everyday life coincided with the change from nomadic 
existence of hunting and food gathering to settlements in communities, the development 
of agriculture, domestication of animals, and craftwork.”

 What led early man to begin using metals in the first place? This was not to make
 better tools or weapons ("A man in search of food or a weapon is in no mood of 
discovery - he only exploits what is already known to exist"). He would have just 
improved the techniques of working with flint and obsidian.

 From about 8000 to 5000 BC the development of the crafts of spinning, weaving, and 
working with pottery came about. These crafts gave mankind time to think. "Liberation 
of the human imagination provided the springboard for almost all progress towards 
civilization as we know it today."

 Innovation and discovery arise out of curiosity. How did man first become aware of 
metals? It would have been a gradual process as they saw that this metal was pot like 
other rock, it seemed heavier, and did not crack when hammered. The first use for 
metals would have been for decoration or ornaments, rather than knives.

 These would have been native metals. These are metals not combined with other 
elements in mineral ores but existing in a pure state. They would have been lying 
on the ground or exposed to the surface. Examples are gold, copper, and iron.

 Gold had been known to the ancients for several reasons. It was soft, the same 
color as the sun, and it didn't tarnish or react with anything.

 The first sign of copper being used is about 6000 BC. It exist both as native and 
in a combined state (as malachite). Copper appears to have been much more common that 
gold or iron. All earliest known metal artifacts are of native copper.

 The earliest dated usage of iron appears around 4000 BC. This would have been 
meteoric iron. This special type of iron contains a high percentage of nickel which 
helps the iron to resist oxidation. Meteoric iron is clearly different from iron found 
on earth and all early iron products would have been from meteoric iron.

To get larger amounts of the metals the process of smelting the metals from ores 
containing the metals were developed. "The discovery of Neolithic man of how to smelt 
metals from ores (where they are chemically bonded to elements like sulfur, oxygen, 
and carbon) must stand as one of the greatest achievements in human history."  

Neolithic = near end of the Stone Age

 COPPER: Copper ore is called malachite. It is green with dark black bands and is 
made of copper, oxygen, and carbon. To smelt copper from malachite there must be two 
conditions met.
1)  must apply heat to 1084° C (melting point of pure copper)
2)  must do this in a reducing atmosphere (this atmosphere is rich in carbon but 
starved of oxygen - the process draws oxygen from the hot ore and 'reduces' the 
ore to molten metal)

These steps to smelting are difficult to perform. A camp fire built on outcrops of 
malachite or using malachite fire stones is usually not hot enough and the carbon 
monoxide in the air (providing the reducing atmosphere) is intermittent. However, 
pottery making and smelting had similar conditions.

  Pottery: Clay is soft and easily shaped when wet but dries in the sun. If clay 
is fired (heated in kiln by stacking pots on top of fuel and covering entire 
arrangement) to about 450° C it undergoes a chemical change and becomes hard and 
waterproof. If it is heated above 1400° C. it undergoes a second change and 
takes on a glass like structure.

The kiln could repetitively maintain a temperature in excess of 1000° C and 
the enclosed space creates a reducing atmosphere. Copper had been used as decoration 
on pottery. By this combination of events and circumstances we believe that copper 
was first smelted in conjunction with pottery making.

 To really improve the process of smelting copper:    
1) use a more enclosed space with more concentrated reducing gases
2) bring ore closer to source of heat by mixing it with burning charcoal
(charcoal = charred wood from fire in reducing atmosphere)
3) blow air into heart of furnace to raise temperature
4) other substances (like iron ore) are added as flux which assist the  
reduction process and improves  separation of molten copper from the melted ore 
called slag

  Problems with copper:
1) copper was attractive and easy to work with, it was good for ornament and small 
tools, but it was too soft to hold an edge
2) by repeated hammering and reheating (annealing) it could be hardened

The first metal added was arsenic - when copper with a bit of arsenic was
worked by hammering it was much harder than pure copper. The bad side effects  
would seem to have prevented it’s use but it was added to copper for many years.                                                                                                                                 
The best metal to add was TIN - why: the way atoms interlock together in metallic matrix                                         

1) the addition of tin lowered the temperature to melt copper (to 950° C)
2) the molten mixture flowed freely into mold
3) during the cooling process bubbles did not for
4) the new mixture of metals was much harder than pure copper

This new metal was called Bronze. By about 3000 BC fearful weapons made of
this new bronze helped create the Bronze Age.    

Bronze is an alloy.  This is a mixture of 2 or more metals melted together resulting in a new metal with new and different properties.  It can usually be separated can be separated back 
into its component metals by heating.

   Later turmoil in the civilized Western world destroyed  cultural and commercial centers. 
Trade routes were overrun and cut. This caused a collapse  of the Bronze Age due to a breakdown in the availability of supplies of tin.

IRON: "Iron has changed life away from agriculture toward industry due to 
plentiful tools and weapons." The main reason iron did not show up in use earlier 
in the Western world than about 1500 BC was that it could not be melted or cast due 
to its very high melting point of 1537° C.

Western approach to iron - the WROUGHT IRON METHOD: At the temperature of bellows' fires iron could be reduced  to a spongy mass mixed with slag called bloom. With repeated hammering the blacksmith could drive out the slag to get a bar of almost pure iron.   However, 
this iron had several bad properties:
1) it was softer than bronze
2) did not hold a good edge 
3) it rusted

There were two ways to improve the iron:
1) steeling: when working with bloom the charcoal and carbon monoxide produced by the
  fire will diffuse into the surface; it the content of the carbon goes to 0.3% it is 
  better than bronze, and it is excellent iron if the carbon content goes to 1.2%.

2) tempering: this involved two steps; a) quenching which is the sudden cooling of hot
 metal by plunging it into water which makes it harder but somewhat brittle, 
b) after quenching re-heat it to about 700° C and then cool it to remove some of the
 brittleness and hardness. "Because they could not heat the iron to its melting point 
and cast it this was to tie them to their anvils and frustrate mass production of iron
goods for a thousand years."

Eastern approach to iron; The Chinese used cast iron for 2000 years before it was used 
in the West. They could melt ' on with better furnaces due to:
1) achieved higher furnace temperatures due to 
    a) horizontal bellows and
    b) double acting box bellows. 
2) the burning of large amounts of high carbon fuel in relation to the amount of 
iron ore being smelted caused carbon monoxide to enter the iron and lower the 
melting point to about 1150° C.

These processes allowed the Chinese to CAST iron. In this process melted iron is 
poured into molds. Cast iron is more brittle and must be made malleable. To do this 
heat the cast iron object between 800 and 900° C in the presence of air. The oxygen 
removes some carbon from the surface which reduces some of the brittleness and forms 
a tough skin on the casting. Casting was found to be much easier to form original shapes.

Gold and lead also had great influences on early metallurgy.

Notes taken from "Out of the Fiery Furnace - The Impact of Metals on the History of 
Mankind" by Robert Raymond.  The Pennsylvania State University Press - 1984