Blue John – New Partnerships

In this post Derbyshire Museums Manager, Ros Westwood, introduces a new partnership with Treak Cliff Cavern and Buxton Artclubs Artbox, supporting Made in Derbyshire.

In one of my earliest conversations with my mother-in-law she told me how much she loved Blue John, the unique blue, purple, yellow and white stone from just two mines above Castleton in the Hope Valley.  So she is very envious that I look after the Buxton Museum collection. The ornaments which bring ‘oohs!’ and ‘aahs!’ from visitors, include the silver mounted milk pail – surely a sugar bowl? –  dated 1803, and the narrow window attributed to John Tym from the middle of the 19th century, as well as unworked specimens, some huge boulders and many small hand specimens (not all of which are pretty!)


Silver-mounted ‘milk pail’, made from Blue John, dated 1803

So if anything is ‘Made in Derbyshire’ it must be Blue John. Formed within the limestone, Blue John is a fluorite. It is not very hard (only 4 on Moh’s Scale of hardness).  The cubic crystals grow in veins through which the distinctive purple and blue layers alternate with white and yellow, providing zig- zag stripes of various intensities. This colour combination makes it attractive for ornaments and jewellery despite being quite a fragile material. There are many ideas of how the colour comes into the stone, whether this is impurities within the fluid, the introduction of hydrocarbons or the occurrence of radioactivity. None really satisfy the mineralogists, yet!

A piece of unworked Blue John from the museum collections

A piece of unworked Blue John from the museum collections

Recently, the museum was offered the opportunity to commission an artwork as part of the Made in Derbyshire campaign. What better suggestion then to explore a commission of worked Blue John to be included in the museum’s new displays.  I invited Vicky Harrison of Treak Cliff Cavern with Gary Ridley and Jack Mosley to discuss the possibilities while looking at the museum’s collection, particularly the unworked Blue John, and then artist Caroline Chouler -Tissier and I went over to Treak Cliff Cavern. It was one of those amazing autumn days and the view as we walked up to the cavern of the Hope Valley was spectacular, in the warm October sunshine.

The view from Treak Cliff Cavern

The view from Treak Cliff Cavern

The view from the workshop was equally captivating, but soon we were deeply interested in learning how Blue John is worked, taking a friable material and making it into artefacts as thin as glass.

In the workshop

In the workshop

Caroline and I were taken through the Cavern, and chanced to see the amazing Witch that flies through it as well as the newly discovered Ridley vein of Blue John, named for Gary Ridley. Meanwhile we discussed our ideas and plans.

To celebrate several events – Made in Derbyshire; Collections in the Landscape and even as an advance 125th birthday present for Buxton Museum (in 2018), the museum is commissioning two exciting new pieces of worked Blue John for the collections.  Importantly, much of the work will be made by people under 25, a chance to learn about geology, engineering, art, and something unique to Derbyshire, all at one time.

Jack has been asked to turn a new chalice for the museum, made from the Ridley vein.  Jack has been working Blue John for three years, and this exciting commission will mean his work will be in the museum collections for all to see. We hope to film him making of it.

Jack at work

Jack at work

Meanwhile we will work with members of Buxton Artbox Artclubs to make the first Blue John window for over 100 years, following in the creative imagination of John Tym.  The Artbox members will visit the cavern and help in the workshop to select material for slicing and polishing. Supported by their artist-in-residence, Caroline, they will suggest ideas of what the finished window may look like. Here at the museum we will look in the vaults at some of the specimens which outwardly look very dull which may find a new life in the window

This will be an exciting creative programme with lively input from many young people. Its early days yet, and everyone is very excited to get things on their way. We will keep you updated through the Collections in the Landscape blog as the work takes shape.  We may need your help to wet-and-dry the Blue John slices – Vicky tells us its takes a long time, but it could be good fun!


Minerals from Ecton Copper Mine

Minerals from Ecton Copper Mine

Azurite on Limonite, Deep Ecton Pipe vein (Buxton Museum).

Buxton Museum has a small collection of minerals from Ecton Copper Mine, including the three specimens shown here.

Aurichalcite, Clayton Adit, Ecton Mine (Buxton Museum)

Aurichalcite, Clayton Adit, Ecton Mine (Buxton Museum)

Chalcopyrite, Copper Pyrite crystals on Calcite (Buxton Museum).

Chalcopyrite, Copper Pyrite crystals on Calcite, Ecton Copper Mine (Buxton Museum).

A recent tour of Ecton Hill and Copper Mine run by National Trust volunteers gave a fascinating insight into where the Museum minerals came from. The mine itself is owned by the Ecton Mine Educational Trust, an independent charitable body. The National Trust have acquired the Engine House.

First we investigated the mine features on the surface and discovered some of the history of the mine. In the afternoon we explored the mine itself and its geology.

A bit of social history …

Copper has been mined where it outcrops on the hill at Ecton since the Bronze Age over 3,500 years ago. Ecton is one of only two known Bronze Age copper mines in England. In the early 1700s the Duke of Devonshire leased the mine out, but as it became obvious it was a rich resource, took back control and developed the mine. It became one of the richest in the world, employing 400 workers during peak production from 1765 to 1789. It is also huge – the mine is as deep as the Empire State building is high! The heyday of the mine was very short. The copper resources were finite and in June 1790 the Times reported the mine had failed and workers had been laid off. It never got back to its former production levels although work carried on for another 100 years. Copper from Ecton was used to protect the bottom of wooden naval vessels from the ravages of worms, and also for the first trans-atlantic telegraph cable.

The Engine House on Ecton Hill. On the skyline behind is a spoilheap from another mine. The bushed below mark an area of Bronze Age mining activity.

The Engine House on Ecton Hill. On the skyline to the right of the Engine House is a spoil heap from another mine. The scatter of bushes immediately below this were pointed out as an area of Bronze Age mining activity.

The dressing floor, where women and children broke the ore out of the rock wound up from the mine. Waste was tipped over the edge.

The stone wall at the back of the dressing floor was built much later, in the 1880s, and formed the back wall of a dressing shed.

The Powder House.

The Powder House.

A wooden lining was attached to the batons to prevent sparks.

A wooden lining was attached to the batons to prevent sparks.

From 1825 a number of companies succeeded each other in leasing the mine from the Duke. The Powder House (for the storage of gunpowder) was built relatively late, in 1884, by Ecton Co. Ltd (formed 1883, folded 1889), but it is likely there was a previous building for the same purpose. It was set away from other buildings for safety and was purposely built with strong walls and a weak roof to direct any blast upward.

In the first early days of the mine, we were told, though it really is hard to believe, that water was removed by a series of rags on ropes which were fed round on pulleys and wrung out. A vertical shaft, the Main Pipe, was excavated from the hilltop and Deep Ecton level was driven in horizontally to meet it. By 1750 the mine was down to the water table. Vertical shafts were taken off Deep Ecton level and ore was brought up and out of Deep Ecton in tubs.

In 1760 a single shaft was sunk the entire depth of the mine from the Engine House.  The shaft allowed air to flow through the mine from Deep Ecton. Pulleys to bring ore out up the Shaft were worked by horses turning a drum in the Gin circle. The circular wall for the winding drum can be seen next to the Engine House.

The Gin Circle.

The Gin Circle.

The Shaft drops ft below this exit!

The Shaft drops for hundreds of metres below this slab!

In 1788 the horses were replaced by a Boulton and Watt double acting steam engine (though the horse mechanism was kept as a back up). Boulton and Watt were the first company to make an engine which would turn something round, rather than up and down, so this was cutting edge stuff. It was the oldest steam-powered mine winding engine house in the world. Horses could move 30 tons per shift, but the engine could move 40 tons.

Gradually the seam became narrower as the miners dug further down and by the late 1790s, it was obvious it was running out. Efforts were made to improve efficiency in extracting the declining resources and in 1804 a new level, Salts level, was driven to bring the ore out at the dressing floor, instead of bringing it up from the outlet of the Deep Ecton level. In 1850 pumping was stopped and the mine finished in 1891.

And then a bit of geology …

Donning hard hats and lamps, we made our way into the hill.

The mine entrance.

The mine entrance, Salts level.

Our guide Pete Webb explained how the surrounding limestone was formed by the deposition of skeletal remains of marine organisms at the bottom of the sea which covered the area around 350 million years ago. At this time Derbyshire was actually very near the equator but has drifted slowly northwards to where we are now.

The horizontal ledge shows the sea floor at the time with 'wayboard' of volcanic ash above.

The horizontal ledge shows a bedding plane, which was the sea floor at the time it was made. A ‘wayboard’, or thin layer of volcanic ash lies immediately above this.

The seabed layer could be seen in the bedding plane at the side of the tunnel, with a layer of grey clay above it caused by volcanic ash. These layers are known as wayboards. Miners would gather mounds of the clay and use it to sit their candles in.

Pete explains the formation of the fault he is standing next to.

Pete explains the formation of the vertical rock fault above his head, and the changes in the angle of the bedding planes we were seeing.

Over millennia, the rock was fractured by large scale movement and volcanic activity. Water bearing dissolved minerals entered the fractures where the minerals crystallised out to form veins of mineral material. It’s estimated this mineralisation took place about 290 million years ago.

Calcite veins - an indicator that other minerals might be present.

White calcite veins – an indicator that other minerals, such as Copper, might be present.

White calcite veins in the rock were a sign that there might be a copper vein and the miners would open up side passages to investigate.

Standing in the fault, near the vertical Pipe shaft. Green malachite (copper (II) carbonate can be seen near the centre of the picture.

Standing in a fault looking up, near the vertical Pipe shaft. Green malachite, a copper ore, can be seen near the centre of the picture.

The Pipe - the original vertical shaft. In 1750 all the ore was taken out of the Pipe.

The Pipe – the original vertical shaft, its shape is very irregular compared to the later Shaft, made when technology had moved on.

Looking down the more regularly-shaped Shaft.

Looking down the more regularly-shaped Shaft.

Guide Pete Webb points out a deposit of malachite (copper carbonate hydroxide)

Guide Pete Webb points out another deposit of green malachite.

Galena, lead ore, can be seen in this crack.

Galena, lead ore, can be seen shining in the crack in the centre of the picture. Here tremendous forces  have moved the rocks so the layers are near-vertical. At one time, we were told, there was a water-powered blast furnace on the dressing floor, for the processing of lead.

To get the ore out, explosive black powder was placed in drill holes. The transition from hand-hewn triangular cross-section holes to cylindrical ones could be seen through the mine. The triangular ones were created by two men taking turns to strike the chisel which was turned between strokes by a third man. Progress was only 5 ft a week, By the 1860s compressed air was being used to drill cylindrical holes. This was generated by a steam engine in the tunnel fed with firewood. It really is hard to imagine what the working conditions were like.

Triangular cross-section hand-drilled hole.

Triangular cross-section hand-drilled hole.

Longer cylindrical drill hole.

Longer cylindrical drill hole.

Iron rails rested on stone sleepers along the sides of the tunnel. It is thought they were arranged like this rather than across the tunnel so that ponies pulling ore along the rails could walk down the middle of the tunnel.

Stone sleepers along the sides of the passage.

Stone sleepers along the sides of the passage, looking towards the exit of Salts level.

Slickenside formation.

Slickenside formation, Salts level.

Before we left the tunnel, there was time for one last amazing piece of geology – a rock at the side of the tunnel showing slickenside, where two sides of a rock fault slid across each other. The slickenside created on the other side of the fault could be seen a little further down the tunnel. The image of Apes Tor, Ecton, below really brings home the forces involved in folding these rocks into such convoluted shapes, which led to the rich mineral deposits being created.


The Beauty of Minerals

Last week I had the good fortune to share an office with Dr Noel Worley, president of the Yorkshire Geological Society, as he cast an expert eye over the Burgess Collection.

Noel and his expert eyes.

Noel and his expert eyes.

The collection includes the research papers, notes and 1966 thesis of A.S. Burgess: ‘The Geology of the Millers Dale Area with Special Reference to the Igneous Rocks’. In addition, the collection also includes 156 thin section microscope slides prepared from field samples by his father, H.W. Burgess. According to Noel, this is one of the most complete collections of Derbyshire Carboniferous igneous sections that exists anywhere.

Some of slides, prepared by H.W. Burgess from his son's field chippings.

Some of the mineral slides, prepared by H.W. Burgess from his son’s field chippings.

Preparing rocks and minerals to a thickness of 0.03mm allows them to be studied through a petrological microscope, such as the one Noel used to check and identify the samples. Having little background in geology or mineralogy, I was unfamiliar with this piece of equipment, and suitably amazed by its capabilities. This got me thinking about how Collections in the Landscape could also help explain the science behind the collections.

Highly amydaloidal basalt with centripetal succession of gret semctite and green chlorite (Crossed Polars)

Highly amydaloidal basalt with centripetal succession of grey semctite and green chlorite (Crossed Polars)

Stained Glass? No! This photomicrograph shows the vivid, striking images produced when viewing the interference colours of a section. As well as being visually stunning, viewing samples in this way can reveal a wealth of information including the composition of different minerals.A petrological microscope uses polarised light and a rotating stage to examine mineral sections. It uses two polaroid sheets, one of which, the analyser, can be moved in and out. Polarisation restricts the electromagnetic vibrations of light to single plane of movement. Confused? Here’s an amazingly simple example even I understood!

Noel's Petrological Microscope

When examined under plane polarised light (analyser out), mineral sections are seen in their natural colour and features such as crystal shape, transparency and fracture can be observed. The limestone section below is seen in this manner. Forgive the quality, it was taken down the microscope on my phone and is pretty terrible compared to Noel’s experienced snaps.

Limestone section viewed with the analyser out (plane polarised light)

Olivine Basalt section viewed with the analyser out (plane polarised light)

When the analyser is included (analyser in) the sections are seen in a cross polarised light. Instead of the natural colours we see the interference colours. As the rotating stage is turned, colours move between a maximum colour and extinction (where they show no colour i.e. black). The nature of these points allows certain minerals to be identified.

The picture below is the same sample as above, but with interference colours. Again, apologies for my awkward camera work!

Limestone section viewed with the analyser in (Cross polarised light)

Olivine Basalt section viewed with the analyser in (Cross polarised light)

I’m fascinated by the aesthetic beauty of these mineral samples, as well as the incredible amounts of information that be gleaned from them. I’d like to think Collections in the Landscape will be able to feature methods of scientific enquiry and give our collections better, richer scientific context.