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  • hbanziger

E - 72 : Did Charcoal fund Alexander?

Updated: May 3, 2021

In my previous blog I was writing about the silver mines of Laurion which made Athens wealthy and powerful. The mines were in operation from 550 to 350 BC and produced 20 tons of silver a year. They yielded 4’000 tons over their lifetime. No wonder some historians estimate that Athens’ Treasury held 3’000 tons of silver during the times of the Persian wars. Am sure the number is exaggerated but the war chest must have been impressive.

The well known "upper town" of Athens

Silver has a melting point of 961 C - close to bronze. For refining and smelting the Greeks used well known ancient technologies. The challenge though was to find the energy necessary for the smelting. Attica was already deforested in the 7th century BC.

Could not find a photo of ancient Greece silver ingots - these are Chinese

Anyway, wood is not ideal for smelting operations which require constant temperatures. When ignited, wood burns first at around 200 C until water evaporates. Dry wood contains up to three times its weight in water thus evaporation takes time. Once the water is gone, the fire reaches a temperature of around 300 C. Now the polymer molecules (lignin, cellulose) start breaking down and burn. Only then carbon starts reacting with oxygen. The fire now glows red-hot and becomes self-sustainable at 500 C. By making fire in a hole in a clay ground, it can reach temperatures of up to 800 C. But it won’t get much hotter. Not hot enough for smelting silver. That is a problem.

These bilingual Ancient Greek Vases showing Ajax and Achilles playing a board game are now in the Museum of Fine Art in Boston

Researching the making of silver got me into pottery – Athens became Greece’s leading pottery producer by the 5th century BC. The classical red black-figure pottery was burnt in three stages. First at 450 C, then a second time at 950 C with damp materials and minimal oxygen to bring the black figurines or background out and a third time below 800 C to re-oxidate the uncovered clay to obtain its red colour. During these three phases, temperature needed to be carefully controlled and maintained at the required level. Something that is impossible to do with wood. So, what did the Athenians do? They also had a silver problem.

The firing process for vases: stage one (raw), stage 2 (pre-burn), stage 3 (black), stage 4 (red)

They imported charcoal from Macedonia from where they also imported timber for their vessels and iron ore for their weapons. Charcoal naturally burns at 1’100 C. By using air bags and blowing oxygen into the kiln, the temperature increases to around 1’500 to 1’600 C. At this point, even iron melts. Controlling the flow of oxygen is thus the key to controlling temperature. Charcoal has another important advantage. Whilst it retains 60% of the volume of wood, its weight reduces by 75%. Compared to wood it is concentrated energy - far easier to transport. Charcoal is light - as we all know from when we buy our BBQ charcoal bags.

Traditional way of making charcoal at 300 C is still used in rural Africa today

Tried to quantify the amount of charcoal needed for smelting silver or firing pottery but got quickly to my limits. Could not find out how much energy it takes to melt one kilo of silver or burn a ceramic pot of 3 kilo. Nor does any of my friends hold a degree in thermo-dynamics. Also, the quantity of pottery produced in Athens eludes me. Does anyone know how to calculate this? Given my passion for cooking I know that you need one kilo of charcoal for barbecuing one kilogram of meat. The following assumptions are to be taken with caution, but I believe they give us some clues of the size of the charcoal trade.

Charcoal righr from the kiln after burning at 300 C

There were about 30’000 households in Athens - burning 1 kilo of charcoal per household and day for heating and cooking is probably a minimum . Makes 30 tons a day. Or 10’950 tons a year.

View of ancient Athens with the Acropolis and the harbour of Piraeus at the back

During my research I found a source that mentioned 40’000 vases a year were made in Athens. A number which would requir 200 family run workshops. Seems plausible. If the average weight of a vase was 3 kg, then annually 120 tons of pottery were produced. Assuming the burning of clay requires three times the amount of energy of food and adjusting for the 3 firing phases, we would get to 1’080 tons of charcoal – a small number compared to the household consumption.

Adding the silver production assuming smelting silver requires 10x as much energy as a BBQ, we would get to 200 tons – again a small number compared to the household needs.

A replica of the Kyrenia boat which was built in 400 BC and could transport 25 tons of cargo

Adding these numbers results in a charcoal consumption of 14’030 tons which would have required 560 Kyrenia vessels (E - 180 ) for transportation. Luckily, most commercial vessels could carry 3 to 4 times more. We are talking about 140 – 150 ships p.a. Whilst there are many assumptions in my calculations, the order of magnitude does not look out of place.

A town like Athens with 200’000 people consumed around 58’500 tons of barley – used the same numbers as for Imperial Rome. Attica produced relatively little grain thus had to import the bulk for its consumption. Piraeus, Athens' well known port, was a busy place and of high strategic importance. Every year, 800 grain vessels (75t cargo) would arrive from the Black Sea, Sicily, Southern Italy, or Egypt. It does not surprise me that Piraeus was heavily fortified and that long walls linked it to Athens' defences. Walls are expensive building projects - nobody builds them just for fun. They are build to protect something valuable.

King Philipp II from Macedonia, Ruler of Greece, Father of Alexander the Great

For centuries, Macedonia delivered timber, iron ore and charcoal to the Greek cities and got paid in silver. Whilst working for and trading with the Greek they learned about the culture and they way they fought. I guess that once Greece run out of silver to pay for its defence, the Macedonians took over – they had the soldiers, the silver, the iron, the timber and the energy. But this is a blog subject for 2022 when we sail from Athens to Istanbul.

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