Early Methods for Breaking Rock Underground
In order to extract the tin ore, the hard rock had to be broken.
Before explosives were introduced, the breaking of the rock was done by hand using hammers, chisels, rock wedges, and poll picks. It was laborious and time-consuming.
At the beginning of the 18th century many mines were using a very old way of breaking rock called fire setting. The Roman’s even used this method! A wood fire would be built next to the rock and would be left to burn, so heating and expanding the rock. Once the fire went out, the rock would cool and shrink. Throwing cold water on the rock would help it cool quicker. This expansion and shrinking of the rock weakens it and eventually breaks it apart. This was very slow and also quite dangerous for the miners.
Gad and feathering
Another old method of breaking rock was by ‘Gad and feathering’. Early miners wedged the rocks apart with simple tools. Gad and feathering was one of the first methods used. A cone shaped rod of metal was driven between one or two thin metal wedges called ‘feathers’. These were placed inside a crack in the rock or a drilled hole. This would be hit with a hammer, forcing the rock to crack.
From the 17th Century techniques for drilling holes in rock were developed. In Cornwall a drill rod, or ‘boryer’ was used to create the hole using a hammer. The boryer was turned after each hit of the hammer, this would chip out a piece of rock. This would eventually create a round hole. The drilled hole was called a ‘shothole’. Gunpowder could be poured into the hole and ignited to blast the rock apart.
Drilling holes in the hard rock of Cornwall was laborious and time consuming. It could take many hours of strenuous effort to bore a 2ft (60cms) hole.
At Geevor, the lodes of tin ore are narrow, miners had to do single hand drilling. The miner held the drill rod with one hand and used the other hand to hammer. ‘Double handed drilling’ were one man held and turned the drill whilst it was struck by two men with hammers was faster and often practiced in the Camborne mines where the lodes are wider.