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Friday 20 December 2019

The Mynachlogddu bluestone quarrying experiment

Back in prehistory -- in the spring of 1986, to be precise -- I was paid a few quid by a Japanese TV company to conduct a scientific experiment into a quarrying technique that might have been employed at Carn Meini or somewhere else during the quest for bluestone monoliths.  This was the fire and water method  -- heating the rock with fire and suddenly cooling it with cold water.  (This all presumes that people wanted to QUARRY monoliths from the living rock rather then picking them up from the ground surface, where they lie in profusion -- but no matter.  Science is science, and a few quid always come in handy.....)

We brought in a huge pile of mature dried logs, built the funeral pyre, and placed the stone (which was as big as we could manage without a JCB) in the middle of it, and lit the fire.  Up it went in flames, and there were several loud cracks from the midst of the inferno.  It was several hours before the fire had died down into a pile of glowing embers and before we could approach close enough to throw bucketfuls of cold water onto the stone.  That was rather dangerous, and we were not sure whether splintered fragments of spotted dolerite might shoot off in all directions. In the event, nobody was injured, and when the scene of the experiment had cooled off enough, we recovered the stone and found that it had indeed been fractured in various (unpredicted) places by the heat of the fire -- and maybe by the water treatment as well.  Anyway, the Japanese TV crew went off reasonably happy -- the bonfire was very spectacular, anyway.......

Carn Meini (Carn Menyn), thought by Thomas and Atkinson to have been a major source for the spotted dolerites at Stonehenge.  It was suggested many times that fires against the rockface would have been set in order to "extract" suitable bluestone pillars........


1.  If this sort of method had been used in a "bluestone quarry" to break off monoliths from the rock face, the amount of timber required would have been phenomenal, and huge amounts of labour would have been needed as well.

2.  The fracturing of the stone was anything but predictable, and I doubt that the process would have been controlled enough to have extracted "marked pillars" with selected dimensions.

3.  Throwing cold water in large quantities onto the heated rock would also have been very difficult, given the residual heat of the fire and the dangers in getting too close too early. First, the water had to be carried in containers up to this difficult location.  A bucketful of water at a time is all that one could reasonably manage -- and throwing water into the glowing embers from above (from the clifftop) or from below would have involved great hazards. 

On balance, the logistics do not really make any sense -- especially since there are pillars and slabs of dolerite lying all over the place across the upland landscape.

That was one of my contributions to experimental archaeology...... actually it was quite good fun.......


Phil Morgan said...

In my old underground coal mining days on several occasions we had to deal with fires caused by spontaneous combustion in the waste areas where the coal had been removed.
The preferred method of extinguishing these fires involved stopping the supply of oxygen to the fire rather even though an excellent supply of water was available.
The use of water was avoided because of the risk of the formation of 'Water Gas' which can be highly explosive.

Phil Morgan said...

And the bit that I forgot ------
Perhaps the organisers were trying to get rid of Brian by blowing him up ��

Using clay, water and freezing temperatures is a far safer way of removing rocks from rock faces.