06-09-2009, 03:32 PM
Quote:I am not a ceramics guy, but from my basic training I have some issues:
1) Ambient humidity - more water will probably be absorbed in wet sites than in dry sites? Much like dendrochronology, reference tables might have to be constructed for different locations...that applies to above-and below ground in equal measure.
2) Waterlogged ceramics - very common in archaeology - will often not survive re-firing, depending on how much moisture they have absorbed. There is a lot of badly fired ware out there as well...how will it be affected by refiring?
3) (out on a limb) Is there different kinds of moisture uptake in different kind of fired ware? It sounds reasonable, but I' m not sure.
Having read the paper through, I can see that none of these will/should make any difference to the measurement.
The uptake of water by the ceramic that is being measured here is ADsorbed water, i.e. chemically bound water, and not ABsorbed moisture (physically bound - wet water, if you like). The ceramic could have been dumped into a lake or river, or left in the desert and it wouldn't matter a jot. What is being measured is a rate constant which applies only to that sample. The re-adsorbtion of water apparently proceeds in two stages. The first is relatively rapid, while the second is very slow and proceeds over time indefinitely. It's this last that is being measured and it obeys a "fourth order rate law", precisely. Moreover, the measurement can be applied to a piece of brick that was made last week, or a sample of Roman brick that was fired 2,000 years ago. The paper's authors think that the technique could be applied to ceramic objects as old as 10,000 years - which would take us back to the very first cities!
I see your point about the second one but two things here: (a) the sample isn't being 're-fired', it's being heated to only 500 deg. C or so and (b) it doesn't matter if the object does fall apart, the measurement can still be made. OK, so you've lost the sample but (except in rare instances) there's plenty of ceramics out there.
Yes, there are different kinds of moisture uptake for different kinds of ceramic ware (depends on the precise mineral make-up of the original clay) - but it doesn't matter as each sample is treated separately.
The technique is self-monitoring in that each sample is treated uniquely - unlike radiocarbon dating where we are using an external standard (which may, or may not, be 'standard' at all). A colleague of mine mused that it might even be possible to date the bottom part of a ceramic altar (when it was made and fired) from the top part (where the sacrifice was carried out and the offering burned), thus showing for how long the altar was in use! Awesome!
Caratacus
(Mike Thomas)
visne scire quod credam? credo orbes volantes exstare.
