An Old Crock
The most famous collaboration between scientists and archaeologists concerns carbon-14 dating, the method by which organic materials such as wood, cloth, cereals or even charcoal, can be dated by measuring the level of radioactivity remaining in the sample. Unfortunately, although charcoal is a frequent find in digs, the most common find cannot be dated by this method - pottery is not organic!
Yet there is a crying need for a method of dating pottery. Although archaeologists talk glibly about "Middle Bronze Age pottery" dating to 1600 BC the plain fact is that all they have is a sequence. We know that Middle Bronze pottery came before Late Bronze pottery and after Early Bronze, but we are dependent upon other sources for the dates which we assign to those periods.
The big problem has been that Egypt, with its list of dynasties, is the sole source for dates for these early periods (in later periods the astronomical records of the Assyrians and Babylonians enable us to be precise and certain in our dates). Rohl, James and other scholars have cast doubt on the chronlogy of Egypt which, if correct, would require corrections in the chronology of Palestine.
In fact, virtually the whole of the Mediterranean would require correcting if the chronology of Egypt were to prove wrong, because everywhere, from Turkey to Greece to Italy and north Africa, relies on contacts with Egypt for dating. Unfortunately these contacts are not always reliable: if we find a scarab of Rameses II in a certain level in Cyprus, for example, we can be certain that the level in question did not date before Rameses, but whether it was contemporary with the great pharaoh or came a century or two after him depends on whether the scarab was kept for any length of time as an heirloom before being lost in a fire or buried in a tomb.
If only there could be some independent method of taking a potsherd or a baked brick or clay tablet, subjecting it to this dreamed-of test and being able to say, "That potsherd - or brick or tablet - is precisely X number of years old." Unlikely as it may seem, such a test has recently been developed and appears to be as accurate as archaeologists could wish.
Firing a clay object in a kiln requires a high temperature and any water in the clay is effectively evaporated by the heat. When it comes out of the kiln, the brick or pot is as dry as the literal bone. However it is no sooner out in the open than it starts to absorb water from the atmosphere - and I am not talking about merely a few dew drops running down the side of a water pot on a hot day. The water I am talking about is actually absorbed by the baked clay - the technical term is "recombined" - and incorporated into the chemical structure of the pottery.
The new discovery is that this process proceeds at a steady rate, governed not so much by the amount of water available as by the laws of chemistry. By measuring the amount of water that the pottery has absorbed, we have a very good guide to the age of the pot.
Fortunately it is very cheap and easy to make that sort of measurement. You simply weigh the potsherd, then heat it to 500°C and weigh it again. 500°C is sufficient to get rid of all the water and reduce the potsherd to its pristine state. The only requirement is for super-accurate scales, but compared with some scientific equipment, such scales are quite cheap and easily available.
A team of scientists from the universities of Edinburgh and Manchester, plus experts from the Museum of London, have been working on this method and over the last year or so have been applying it to range of objects whose age is known with a fair degree of precision - Roman, mediaeval and modern pottery.
For example, the team got hold of a piece of Roman brick known to be 2,000 years old. Their calculations gave it an age of 2001 years. Another brick whose age was believed to lie between 708 and 758 years was found to be 748 years old.
The smug smiles on the faces of Dr Moira Wilson and her team from Manchester University turned to dismay, however, when they tried the next sample - a piece of brick from Canterbury which was known to be mediaeval in date. They carefully weighed their sample, fired it and weighed it again, but when they did their sums the answer came up 66 years old. Accusations of carelessness hovered in the air while they frantically redid the maths and re-weighed it (of course, it was too late to weigh it for the first time or to re-fire it). When the answer was still 66 they looked elsewhere for the answer and discovered that the building from which the brick came had been seriously damaged during a fire caused by German incendiaries during the second World War. The heat from that fire had "reset" the clock, so to speak.
So far the team has tested objects up to 2,000 years old, but the scientists believe that with more careful weighing the method could be used on objects up to 10,000 years of age, which would put it on a par with carbon-14 dating. It will be interesting to see whether the method comes up with significantly different dates for the earlier periods.
Of course the main problem will be the process of correlation. As mentioned elsewhere on this site, when carbon-14 was being tested the scientists found it necessary to introduce a 600 year "correction" at a certain point. Their measurements of radio-carbon decay told them that the object was - say - 3,200 years old, but the archaeologists assured them that it was, in fact, 3,800 years old and the scientists, unaware of the problem of the "Dark Ages" exposed by Peter James and others, went along with the "experts".
If the pottery evaluations come up with a similar discrepancy, the pressure to re-date and reform Egyptian chronology will, I hope, become overwhelming. If it doesn't, then that will have other implications.
Watch this space!
© Kendall K. Down 2009
