Carnglaze Slate Caverns

Today we visited the slate mine at Carnglaze.

 This is the only underground slate mine in Cornwall and has 3 large chambers.  The slate was mainly used for roofing.

In the 1700's miners wanted better quality slate so they started digging underground.  This also meant that they could work in all weathers. The slate mine was always about 10 degrees celcius which was a comfortable temperature all year round.

Instead of using ladders they used the rubble left from the mining to climb on and slowly dig the mine upwards.

The only light they had was candlelight.  The men worked in teams. There were 5 men in a team, 3 drillers, a splitter and a dresser.  One man would hold the drill bar and the others would hit it with sledgehammers. Doing this they could drill a hole about 1 foot deep in an hour.  One of the safety methods they used was that the man holding the drill bar would often be a young boy of about 14 years old and he would be related to the men with the hammer.  This was because the men with the hammer would be more careful with someone who was related to them.

These are the steps down into the chambers underground

The hole was packed with black powder which wasn't as dangerous as dynamite.  Each hole would blast about 1 metre cubed of rock.  This was done by lighting a safety fuse in the black powder which burnt at the rate of 1 foot a minute.  They lit the fuses at the end of the day as the men were leaving so the dust could settle before the next working day.

this is a pile of rubble that the miners would use to stand on to dig deeper into the ground

The next day the men would clear out the large blocks of slate and take then to the entrance of the cave where the splitter worked because he needed shelter and daylight. We saw a man demonstrating how to split slate when we visited the Llanberis slate museum in Wales.  He could split the slate into pieces only a few millimetres thick.  The other member of the team was the dresser and he had a knife called a zax so he could shape and trim the slate into the sizes they wanted.

The miners were paid by the piece and they were paid in tokens which they could only spend in the  mine shop. I think this system is horrid because if you got paid real money you could go to any shop and buy probably more than you could in the mine shop.

In the mine are 2 lakes.  One is called the baby pool and although the slate is waterproof water can still find ways through the gaps and cracks in between the rock to get into the mine.  The pool looks very shallow but it is actually 2 metres deep.  The water in the pool looks green but is actually isn't. The reason it looks this way is because there is a mineral in the rocks called mica which makes the water look this way.  This is why the sea in Cornwall always looks bluey green in the sun.  The water in the pool slowly runs underneath the mine floor and finally makes it way to the river below.

The other pool is called the Mother Pool and it is quite a lot larger.  It also looks shallow but is is 9.5m deep.

It was really interesting visiting the mine and learning about how they got the slate.  The pools were beautiful.