Dartmoor Tin Smelting

  IN PURSUIT OF ANCIENT DARTMOOR TINNERS' SKILLS

Ian Kirkpatrick 1985

                                   

A friend mentioned the whereabouts of some cassiterite (tin ore) left behind by the Dartmoor tinners' during the last century.

We set off for the location armed with the tools of the trade. We made our way into the depths of north Dartmoor. We collected a few heavy specimens of tin stone and returned home.

Crushing the stones turned out to be a muscle wrenching task. Unlike the ancient tinners’ I had no help from water driven stamping mills. A whole day was spent pounding rock until I was left with a biscuit tin full of flour-grade dust and an aching back.

We now had to simulate a tinners' buddle.

We used a miner’s pan in order to separate the heavier ore from the rock. At the beginning of each wash the water became very murky, however the continuous circular motion eventually revealed a dark brown sludge at the bottom of the pan. After washing the biscuit tin full of rock dust we were left with enough tin oxide to fill a container 2”x 2”x 1”. The weight was quite considerable.

An added complication was I had succeeded in clogging the drain!

Off to the library next, for a bit of swatting on how to produce the metal tin. These days Google would have provided the answers!

Tin sand (tin oxide) must be combined with a flux and then burnt. The flux has the properties of producing carbon monoxide, which combines with the cassiterite (SnO2) to relieve the mineral of its oxygen, thus leaving the metal tin.

All this is OK in theory.

Home again laden with various items of equipment for a chemical experiment – charcoal block, a methyalated spirit burner and a blow pipe.

The experiment starts – small quantities of flux and ore were seated in a small depression in the charcoal block and the flame from the burner was directed by means of an air stream from the blow pipe onto the mixture which in theory should have produced a bead of tin.

I tried and tried without success; all I managed to produce was a grey looking slag.

One evening however the family were visiting and I began to demonstrate the technique, with much blowing, blood, sweat & tears no result. The family unimpressed deserted the sinking ship.

Not to be beaten I continued, in time a reaction occurred, the hot mixture emulated a small volcano, immediately the family returned; suddenly a molten bead rolled off the charcoal block and disappeared like Halley’s Comet across the table and onto the floor, never to be seen again. I had many more hours trying to repeat the experiment without success. Doubts began to arise in my mind as to the quality of the tin ore so I telephoned Cambourne School of Mines who very kindly offered to analyse the sample. I duly packaged a sample and posted it off.

A week went by before the School of Mines contacted me wanting to know the exact location from where the tin came from. The original analysis had revealed gold fragments! Great excitement ensued until I confessed I had pounded the ore in a crucible once used to melt brass – oh dear! At least the ore sample was proved to be cassiterite.

Finally in desperation I decided that what was needed was a furnace, so off to the local dump to acquire some fire bricks which had been used in a storage heater.

A temporary furnace was constructed on a bench in the shed. The ore and flux were layered alternately with charcoal in the furnace and the whole thing ignited. Combustion was slow so I speed'ed things up a bit with the blow end of a vacuum cleaner. This resulted in the bench catching alight and clouds of dust being blown out of the chimney, filling the shed with smoke and fumes. Caroline my wife popped her head around the door and quickly departed, I was left alone with a black face and tin dust everywhere. Morale was distinctively low.

What had I achieved? Answer - a dirty shed, a dirty face and a pile of ash.

Decided the sensible thing to do was to repeat the experiment in the garden to avoid a visit from the fire brigade!

The furnace was reconstructed outside and stacked with layers of charcoal, flux and tin ore. A good burn was created. I was expecting molten tin to run out of the channel at the bottom of the furnace but nothing appeared!

Very disappointingly I began dismantling the furnace. I swept the residue from the fire into a pan and washed it, this left the heavier particles. Examining the residue I was very excited to find small medallions of soft white metal – tin, eureka – success! I collected all the samples and melted them together to form a good size ingot .75”x .25”x .19”.

                            

Statistics – 

Ore bearing rocks collected 62.6 kilograms

Total crushed ore 1.169 kilograms

Tin metal produced 205.54 grams

Look out the International Tin Council!

 

In conclusion I can honestly say that those ancient tinners' deserved every penny they earned. Needless to say the cost of the whole experiment will remain a secret, but all in all it was great fun!

Comments