Friday, December 15, 2017

A Technical Appendix to Postblogging, October, II, with Segue to the Early Iron Age Rebirth of the State: Axial Compressors, Smelting and Bullion

In October of 1947, the owners of one of the first industrial axial compressors ever built, donated it to the Science Museum, Kensington, London. After a long and honourable career smelting lead, beginning in 1909, it would have an afterlife enlightening museum visitors on, uhm, axial compressing. 

 This is another axial compressor application, the Bristol Olympus, as used in the Avro Vulcan V and the Aerospatiale Concorde :

CC BY-SA 3.0,
If, like me, you waste valuable morning writing hours dallying on the Internet, you may have encountered Stumbling and Mumbling's discussion of "technological regress," the opposite of technological progress. It uses the Concorde as one example of this regress. You may have also encountered the commentators arguing that it isn't really technological regress, since Concorde was expensive, and now flying is cheap. This, of course, would be a perfectly plausible argument were the Olympus and Concorde incapable of improvement. Which I guess they are! Certainly, we can't afford the R&D and capital investment effort to improve them, so we'll have to settle for being able to use our personal entertainment centre during our twenty hour flights to Asia.

At risk of indulging my worst habits of digression and irrelevance, I want to quote now from a forgettable space opera by the high-powered 50s duo of Frederick Pohl and Cyril Kornbluth, called Search the Sky. It's up at Project Gutenberg if you want to read the rest of it. 
Ross stood on the traders’ ramp, overlooking the Yards, and the word kept bobbing to the top of his mind.
. . . .
About all of Halsey’s Planet there was the imperceptible reek of decay. The clean, big, bustling, efficient spaceport only made the sensation stronger. From where he stood on the height of the Ramp, he could see the Yards, the spires of Halsey City ten kilometers away—and the tumble-down gray acres of Ghost Town between.
Ross wrinkled his nose. He wasn’t a man given to brooding, but the scent of decay had saturated his nostrils that morning. He had tossed and turned all the night, wrestling with a decision. And he had got up early, so early that the only thing that made sense was to walk to work.
And that meant walking through Ghost Town. He hadn’t done that in a long time, not since childhood. Ghost Town was a wonderful place to play. “Tag,” “Follow My Fuehrer,” “Senators and President”—all the ancient games took on new life when you could dodge and turn among crumbling ruins, dart down unmarked lanes, gallop through sagging shacks where you might stir out a screeching, unexpected recluse.
But it was clear that—in the fifteen years between childhood games and a troubled man’s walk to work—Ghost Town had grown.
2Everybody knew that! Ask the right specialists, and they’d tell you how much and how fast. An acre a year, a street a month, a block a week, the specialists would twinkle at you, convinced that the acre, street, block was under control, since they could measure it.
Ask the right specialists and they would tell you why it was happening. One answer per specialist, with an ironclad guarantee that there would be no overlapping of replies. “A purely psychological phenomenon, Mr. Ross. A vibration of the pendulum toward greater municipal compactness, a huddling, a mature recognition of the facts of interdependence, basically a step forward....”
“A purely biological phenomenon, Mr. Ross. Falling birth rate due to biochemical deficiency of trace elements processed out of our planetary diet. Fortunately the situation has been recognized in time and my bill before the Chamber will provide....”
“A purely technological problem, Mr. Ross. Maintenance of a sprawling city is inevitably less efficient than that of a compact unit. Inevitably there has been a drift back to the central areas and the convenience of air-conditioned walkways, winterized plazas....”
Yes. It was a purely psychological-biological-technological-educational-demographic problem, and it was basically a step forward.
Ross wondered how many Ghost Towns lay corpselike on the surface of Halsey’s Planet. Decay, he thought. Decay.
But it had nothing to do with his problem, the problem that had kept him awake all the night, the problem that blighted the view before him now
I have no idea where Pohl and Kornbluth stole the nightmare of the abandoned blocks of the Ghost Town of Halsey City from, although Fortune's big, wartime articles on "urban blight" come to mind, ahead of the expressways and housing projects that, as it turns out, made it all worse. It's the special miracle of juvenile readings that they stick with you for life, and I am often reminded of the glib specialists of Halsey's Planets when I read that:

 "Concorde was never the future. It was always the last gasp of an outdated conception of blue-riband travel reserved for the elite (which lives on in the space travel dreams of Branson and Musk). Progress in aviation has meant democratisation - more people being able to fly - which has required significant technological progress, just not the sort focused on raw speed or "elegance". 
(Although the rest of his points have merit.)

I am also reminded that there is nothing more normal than for an archaic state to fail. The extraordinary thing about the Late Bronze Age failure of the state and the /Early Iron Age revival, is that the state roared back with a vengeance, on the strength of a dazzling array of innovations. Until I am persuaded otherwise, I am taking iron, and the related/necessary exploitation of temperate, wet forestland, as the key innovation, but that is not the one I am talking about today!  

Archaic Corinthian stater, so old that it spells the city's name with a "Q," as they did back in the day. That is, key point, well before the electrum Lydian issue of Alyattes II that still gets pride of place as the "first" coinage.

Why silver and the rise of coinage? Because it seems like a brief but interesting topic. It has risen organically from my techblogging, and I have some interesting factoids to share. Ideal for posting on a short week. So, without further ado, factoid number one: Last week, I came across the extraordinary observation that silver is not known in Danish archaeological contexts before 100BC. 

What does this mean? Heck if I know. Denmark's "Silver Age" is special, because it begins with a very loud bang with the Gundestrup Cauldron. The art history of the cauldron has launched a thousand academic careers, in all directions (images of Celtic gods? Akkadian kings?). All I am going to say is that the absence of earlier Danish silver would seem to be pretty clear evidence that Something is Up.

Without further spoiling later posts, it seems a viable theory that that "something" is the quickening of military activity after 700. Hans van Wees argues that the Athenian state's extraordinary classical finance, which spent as much weight-of-silver per head of population as the Dutch Republic at its height, was driven by the need to raise a large navy. (It is estimated that the Classical Athenians extracted 30 tonnes of silver from the mines at Laurion, compared with the Roman empire-wide production of 200 tons, giving the Romans a circulating mass of 10,000 tonnes in the Third Century, ten times the amount circulating in Carolingian times. This has been factoid 2.) 

Timing and use suggests an Ideological Explanation for the claim that coins were first minted by the Lydian kings. On the one hand, the "Man of Lydia" has an outsized role in the early Greek imagination. How else does one explain the fact that when the Laconians set out to create a capital city, they gave it the same name [Sparta/Spardis] as the Lydian capital? Less speculative is the fairly obvious point that Herodotus tells us all about Croesus. On the other hand, many Classical writers thought that navies were dubious and subversive institutions and were reluctant to believe that Solon, that wise old lawgiver, was motivated largely by the need to provide for a nasty, democratic navy

Is van Wees right that these earliest authors minimised the sophistication of the earliest fiscal state for ideological reasons? It's worth considering. It's also worth considering that silver minting was popping up all over the Aegean world, at more-or-less the same time, around 700. With which key era I will leave that hanging and pass on to metallurgy and the technological appendix part of this discussion. 

Silver is a transition metal in the same block of elements as copper and gold. It is highly lustrous, ductile and soft; and traditionally is one of the "noble"metals, in that it does not oxidise, except in the presence of sulfides, which makes it a noble metal, but less noble than gold. It also makes "native" silver, that is, silver occurring as shiny nuggets, notably in placer deposits, much rarer than gold, although not unknown, and available to taunt our Neolithic ancestors with the possibilities of a world beyond stone --although not, of course, to anywhere the same extent as copper. 

Archaeology at Laurium, ancient Thorikos, has satisfactorily established that mines there were worked from Neolithic times, at which point terminological inexactitude becomes vexing. 

 There are a lot of ancient mines around in the deme for archaeologists to explore in search of science and headlines. For example, the recent discovery of a mine more accurately dated to 3200BC than most has inspired headlines about a "five thousand year old silver mine on the shores of the Aegean." This would seem to imply that we know that the mine was intended to produce silver, and, in fact, this is something that we can know (although the archaeology would have to be somewhat indirect, as it is unlikely that the silver would have been cupellated  in the mines, so you would have to associate it with a remote site with evidence of cupellation). There is, however, no evidence that we do know that. However, there is no reason that the mine could not have been aiming for copper or lead. 

Turning to literary sources, mainly because I have them, Benjamin Foster is very, very impressed with the "Age of Agade." 

It turns out that the Ishtar of Agade was so impressed with those manly biceps that she made Sargon I the first ruler of the Four Lands (both banks of both rivers) and the Four Quarters. Sargon, the goddess raised up from nothing, for he stands at the head of a curious, antiquarian list compiled by a later scribe of "kings who were not sons of kings." This may be a bit of a myth. Sargon never called himself "son of. . ." but none of the notables of his empire did. Normal subjects continued to be known by their father's names, so this is very much an official court style, and we should not draw the inference that the origin myth in the later Epic of Sargon is historically accurate. What we know is that Sargon was militarily and politically active and successful, that he exalted Agade/Akkad above all the cities in the world, and that he established a sovereign party (in Wikipedia's neutral phrase, since it turns out that "empire" is controversial), that, under his grandsons, became a self-confident, assertive, and wealthy cultural powerhouse. Akkadian imperial styles defined everything from royal titulature to calligraphy for as long as the cuneiform tradition survived, and perhaps beyond; and Akkadian imperial art and documents have been widely recovered from Iran to Syria. 

Thus Foster's argument that we can see an Akkadian Empire in the archaeological evidence, and that on its strength we should see a regime with a particular interest in worldwide trade relations, in particular. I'm not going to say that that is Foster's main concern, but it does lead me back from this digression to silver, first attested as a medium of exchange under the Akkadian rulers. It was rare and expensive: 1 shekel of silver (7 to 17g in general) was worth 195 shekels of copper in the pre-Akkadian period, rising to 1:240 at the height of the empire, although one could also formulate that as copper becoming cheaper. One document references an allocation of four tons of copper to smiths for production of tools, while totals in the range of one talent (15kg) are the largest sums of silver referred to, a princely sum used to buy and sell large tracts of land, with 300kg of silver representing "schoolboy fantasies of unlimited wealth." To put it in more concrete terms, in a year of normal harvests, a shekel of silver was worth 300 litres of barley. In summary, silver existed, in standardised weights, and was used for very large transactions; but very little has been recovered in Akkadian contexts. The numbers really do reflect its rarity.

To take other metallurgical evidence into account, the Akkadians were well aware of the existence of bronze, and made it; but the tools that have been recovered from numerous and ill-analysed Akkadian hoards are entirely of copper. Pure copper, or copper adventitiously mixed with minor alloying metals such as zinc and arsenic, represents the normal tool material of the empire. Tin is rare, and one Akkadian king celebrates the successful casting of a tin statue of himself. (It's almost as though the idea of technological progress wasn't invented last week!) We really are at the dawn of the Bronze Age, here.

This being the case, it is reasonable to ask how Akkadian silver was extracted, to the extent that it was not native metal entirely. The Wikipedia article on silver mining, for what it is worth, describes the production of silver by heating silver-rich sulfide minerals in salt, producing AgCl, which is then chemically reduced. This is a neat story (though higher above in the article prefers to produce silver oxides by exposing ores to alkalis, then precipitating out metallic silver. Either method, if truly distinct --I'm a little lost, here and haven't the time to sort it out-- bears interesting comparison with the Akkadian sources that assert that faience (glass) is produced in marshland cities and is therefore not worth very much --presumably because Akkadia, at the margin of the steppe, looked down on the production of the Sumerian cities of the southern alluvium, with their ready access to sodium-rich marshland , from which alkalis and salt can both be extracted.  

So far, then, chemical extraction from silver-rich ores would seem to suffice to bring silver into circulation in the earliest stages of metallurgy, in which refining copper and tin are the peak of practice. Turning to the evidence from Laurion, this had changed by 1500BC. Whatever the earlier use of the mines there, and I, personally, am betting on copper production, there is that indisputable chemical evidence for the extraction of silver (and lead) through "pyrochemistry."

What happens here is that the lead-containing mineral, normally galena, is introduced into a blast furnace along with a flux of limestone, iron and silica, and charcoal, as well as "caustic material," and exposed to an "oxidising environment." That is, it is blown and heated until the lead is separated from the mineral and fully oxidised. At this point, the air is cut off: the molten mass begins to produce carbon monoxide, which creates a reducing environment that draws off the oxide. The flux then carries the molten lead metal down through the furnace, where it is drawn off at the bottom. The resulting material separates into a dross-and-copper containing top layer, and a "lead bullion" of lead and (most of the) original silver, below. If you're after copper, the top layer is taken off to be smelted again, and the lead bullion left over is interesting primarily because, if the silver content is high enough, it has a lustrous, silvery finish that makes for interesting objets d'art.

If you're after silver, on the other hand, the bullion is now introduced into a crucible of characteristic  "cup" shape

George Bauer (Agricola)'s illustration from De re Metallica, which you will have seen if you followed the earlier link to the Wikipedia article on cupellation, shows an assay cupel being heated in a furnace. The furnace is lined with a "calcareous" material such as seashells, animal bones or wood ash, since the lead cannot be brought into contact with silicates at this stage. The lead in the bullion melts at 327 degrees, but forms an oxide and solidifies until the cupel reaches 888 degrees, at which point the the lead melts and begins to form lead monoxide. Capillary action draws it into the calciferous lining, and the silver is left to melt at 960 degrees, solidifying out on a bed of lead monoxide mixed with ashes and such, the "litharge." The litharge is now available for the production of red glaze for Attic pottery, while the and solidifies as a tiny little disc on a bed of litharge of characteristic shape that tells the archaeologist right away that cupellation is going on at the site. 

Apart from the wild-eyed speculation that the characteristic shape of the refined silver ingot might explain the adoption of coinage as well as anything --resmelting silver and shaping it can be quite dangerous if you don't know what you're doing, due to "sputtering"-- the obvious point to draw from this burden of knowledge, all too hastily and superficially gained, I concede, is that when we are talking about the Athenian silver mines of the Classical age specifically, there is every reason to shift from a "supply side" analysis to a "demand side." It is not that the Athenians chanced to discover a rich vein of silver and became rich enough to afford a fleet in 483BC as that they were looking for such a vein, and willing to invest in the refining effort needed to produce all of that silver. 

As far as justifying a blog post, that will have to do. Silver isn't like gold. You don't just find it by individual effort in a placer mine. (Well, you do, just not very much of it.) It has to be refined and extracted, and it requires a significant investment in industrial production before you get to the point of producing the silver to begin with. The industrial products --of forest and marsh-- are useful for other things, of course. It might be that these industries come first. Whether or not that is the case, the emergence and rapid spread of silver coinage on the shores of the Aegean at the dawning of the Early Iron Age is as much evidence that Something is Up here in 700 as the Gundestrup Cauldron is evidence for the same in the Denmark of 100BC. A spread-from-centre-to-periphery model will do  here, and it is mediated by the rise of money.  


  1. This is about coins, not money. Money began from tokens denoting transferable debt, and becomes more general (more transferable) and less personal as it evolves. So the earliest money is a clay token entitling the bearer to, say, 200 litres of barley and a sack of onions from the temple at Uruk. The current version is a letter of credit entitling the bearer to load 100,000 tons of iron ore, payment backed by the China Overseas Bank, verified by Royal Bank of Canada (or some such). These are the ordinary stuff of commerce. Silver (or gold) are by custom the standard by which all other debts are judged, as being the most widely accepted tokens and the least burdened by judgements about the issuers creditworthiness. Coins come in with mercenaries, who have no connection to local mercantile credit and want portable wealth (there is a centre-periphery flow here, as the mercenaries are mostly from the edges - Thracians, Scythians, Greeks, Celts...)

    The mines of Sunion allow Athens to issue more debt, and get better trade terms by being more creditworthy.