The lack of replies - other than Silas Hurry's helpful e-mail - over whether anyone's converted Harrington and Binford clay pipe approaches to metric measurements, leads me to strongly suspect that the answer is 'no, not really'. While Silas has very kindly agreed to get a copy of the relevant original GWS transcript to me when he has a spare moment, that still won't basically solve the problem that metric drill bits increase in different increments than their Imperial cousins. A straight metric conversion only becomes possible if we can convert 64th" / .4 or 128th" /.2mm increments to formulae that permit measurement in .5mm.
On that basis, I've put together a very preliminary rough draft metric Harrington pipe stem dating table. I stress that I have -not- tested it. Please consider this a hypothesis only.
The basic principle at work is the observation that the ratio between Imperial (or 'English' if Americans prefer) drill bit increments and metric drill bit increments is essentially 4:5: where Imperial drill bits increase by 0.016" / .4mm per increment, a .5mm increment increase in a metric drill bit equates to an increase of 0.020".
The different period increases on the Harrington table are 30 years, 30 years, 40 years, 30 years, and 50 years. Assuming a direct ratio translation, this gives us 37.5 years, 37.5 years, 50 years, 37.5 years, and 62.5 years on their metric equivalents. Taking the casual liberty to round up 37.5 to 40, and round down 62.5 to 60, this potentially gives us:
1590 - 1630 = 3.5mm
1630 - 1670 = 3mm
1670 - 1720 = 2.5mm
1720 - 1760 = 2mm
1760 - 1820 = 1.5mm
This is a bit crude, and won't be as 'accurate' as Harrington's figures (or the St. Mary's City GWS figures) because there are fewer increments, but it strikes me as at least a decent starting point for testing and to use as a preliminary rough training model in countries which use metric. I have a small late 17th- to early 18th-century assemblage in front of me from Norwich (UK) that I'll use as a preliminary test in the coming weeks. It looks like I can source 64th of an inch drill bits as well (there just weren't any in the office), so I should be able to generate 'control' figures based on the original formula to test against the new metric
On the basis of the above 4:5 core ratio, it's hypothetically possible to convert the Binford dating formula by replacing the latter's '38.26' with '47.825' (38.26 / 4 = 9.565 and 47.825 / 5 = 9.565). I'll try and test this with the Norwich pipes as well since I also have the control of being able to date the latter's dates from contextual and other data.
I thought I'd try and open this up to discussion and ask if anyone might have any thoughts on the above? Particularly, am I mad, or is this potentially useful and worth continuing with? (not that the two are necessarily mutually exclusive)
Alasdair
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