Monday 23 May 2016

pennyweight

The other day, I referred, quite casually and without explanation, to a 10d nail and a 16oz hammer. It's been a while since I wrote about weights [troy] and measures [temp] [tile], but it is fascinating how we have developed such diversity in describing commensurate things. The French put a bit of a kibosh on the romance of it by developing a system that dimensioned the whole world in multiples of 10. When I lived in Boston, I was intrigued to hear the gaffer ordering a packet of 10d [10-penny] nails for rough carpentry.  We didn't use that term on this side of The Pond: he was talking about 3in nails [that's 76mm to everyone else on the planet]. When it came to ordering the lumber [not timber] he asked for 2-by-4s [not 4-by-2s]. They make much of the fact that England and the US are two nations separated by a common language but this is greatly exaggerated - nobody is going to die if you use the wrong term here and no mistake can be made about what is meant.  The 16oz hammer? That would be one with a head weighing  [a nominal] 16 ounces = 450g.

Turn out that 10d nails are so called because in the 1300s that was the cost of a 'long hundred' [=120] of the article. Longer nails were naturally more expensive. In old accunt books you can find such entries as ffor ii c of vi peny nayle = xij This solidified into a convention that a 4d nail is 1.5 inches long and each additional quarter inch added a penny [d] to the cost.  Beyond 10d the relationship stops being linear.  Interestingly, the actual cost of 10d nails didn't change in a straightforward fashion: as inflation ate into the value of money, so the technology for making things like nails got more efficient. In medieval times, each nail had to be hand-forged but when machines replaced artisans, the real cost of making nails fell by 1400x [!!] in the 150 years between 1790 and 1940. When we look at the elegance of scarfed joints between baulks of timber in medieval churches, where the two lengths of wood are mortice-and-tenoned together and possibly held by a drilled hole and wooden peg we wonder at the skill and time required to achieve the engineering requirements. This solution was driven, at least in part, by the fact that nails were of astronomical price but time and wood were cheap. Apparently old buildings were burned to the ground <carbon-footprint frisson> to recover the nails.

There is certain machismo in being able to whack nails into boards with as few blows as possible. You can take part in nail-driving competitions in fairs around the country during the Summer. Only in Russia do they dispense with the hammer! I thought that was as daft as it gets but in Germany real men drive nails into the ceiling by juggling three hammers.