Web
Analytics
Report - - The China Clay Industry in Cornwall and Devon | Industrial Sites | 28DaysLater.co.uk

Report - The China Clay Industry in Cornwall and Devon


Terminal Decline

28DL Regular User
Regular User
The history of china clay in Cornwall and Devon

China clay is decomposed granite where the feldspar had changed into a fine, white powder known as kaolin. Certain parts of the granite uplands, both in Cornwall and Devon process this substance. Today china clay is only mined in the Hensbarrow Moors north west of St. Austell and at Lee Moor- on Western Dartmoor, though in the past kaolin has been extracted on Bodmin Moor, West Penwith and Tregonning Hill, where it was first ‘discovered’ by William Cooksworthy in the 1740s.

In China kaolin had been used since AD700 to create a particularly fine type of pottery- porcelain but the Europeans were unable to discover its secrets. The Cornish kaolin was known to be exceptionally heat resistant and used in tin smelting, but it was Cooksworthy who discovered its potential for pottery manufacture.

The first clay pits were small, compared with today’s workings and tended to be very shallow to avoid the cost of pumping. The processing of the clay was particularly inefficient as clay was dried in the open, often taking several months. Artificial drying commenced in the 1840s, resulting in a great increase in production. Steam engines also began to appear at this time to pump the clay slurry, allowing pits to become much deeper. By 1914 there were 159 active clay works though many were small pits, controlled by independent companies but following the First World War, consolidation was needed to expand existing pits and modernise its production methods. In 1919 three of the largest companies amalgamated to form English China Clays Ltd (ECC). Many pits were closed in the Second World War when demand drastically fell and rationalisation was needed. Several of these pits are abandoned to this day, giving a good insight into historical methods of extraction and processing.

In 1999 ECC was acquired by the French company Imetal who subsequently changed their name to Imerys who have since closed several major pits and processing facilities as they move there operations abroad. In 2012 they bought the last independent clay company: Goonvean and Rostowrack China Clay Co, giving Imerys complete monopoly of the industry.

The Moors around St. Austell are now dominated by the huge mountains created from the waste rock and sand extracted from vast pits. Unlike the tin and copper mines, the china clay industry has received very little attention, mainly because this is still a major industry with many important sites left to decay. Much of the archaeology has been destroyed over time as pits expanded taking engine houses, dries, and houses with them. It is sad to see what has been lost since the Cornwall Archaeology Unit carried out an extensive survey in the early 90s. Major losses since then include the 1930s power station at Drinnick, Charlestown foundry, the house of last pumping engine to work in Cornwall at Greensplatt- it stopped working in 1959 and the engine was removed in the 70s and is now at the Poldark museum, the village of Greensplatt, and Goonvean engine house which still contained its engine until demolition when it was removed to Hayle in 2008. What is partially sad about its loss, together with the earlier engine house and splendid pan kilns is that when Imerys took over the company only a few years later, they abandoned the pit, making the obliteration a site of huge importance completely pointless.



Over the past two years I have visited and recorded a great number of the surviving remains and have decided to use my photos to show the process of clay extraction and what survives. I still need to explore the other areas of clay extraction in Cornwall and Devon, but this report virtually covers the whole process.



0.3 DSC_1610 2.jpg


English Clays Lovering Pochin logo on the wall of a concrete block works. ECC later merged with two other companies becoming ECLP before ECC acquired the rest of the shares in the 1950s


Pre-war china clay extraction process:

There is a great deal of remains from the traditional process of china clay extraction, though this is only a fraction of what there once was as pits enlarge, removing all traces of earlier workings.

0.1 IMG_20180907_195828.jpg


0.2 IMG_20180907_195841.jpg

Diagrams showing the typical arrangement of the pre-war refining and drying process



  • First the clay pit itself where clay was extracted from the rocks and dissolved in water
01 DSC_7946 2.jpg

A typical old clay pit seen from a tip. This was one of many which closed in 1942 and never reopened, showing the steep sides and a small tip as seen from the largest sky tip. Note the waterline halfway up the cliff face, a pit recently broke into the older workings though this now seems to have been abandoned in the early stages


02 DSC_0411 2.jpg

Rather than going down, this earlier pit was cut into the side of a valley. I took this photo looking back towards the entrance of what now appears to be a natural landscape


  • Next the waste material is transported to the tips
China clay extraction produces a vast quantity of waste rock and sand: for every ton of clay produced, 8 tons of waste have to be removed. In the early days this was simply done by tipping material in flat topped finger dumps, similar to those seen at a number of granite quarries but as the number of works increased, clay produces couldn't afford to waste so much land which lead to the birth of the sky tip. Waste was hauled from the pit via an incline and deposited at the top, extending the dump. These pyramids quickly led to this area becoming known as the 'Cornish Alps'. Sadly, many of these sky tips have been flattened in the wake of the Aberfan disaster to be replaced by strange stepped hills.

03 DSC_2298 2.jpg

One of the finest remaining sky tips, 60 years ago the whole area surrounding St. Austell was packed with dozens of white pyramids, but now the few which survive are often hidden in forests of rhododendrons

04 DSC_4772 2.jpg

Looking at the sky tip where I took the first photo from, seen from the other large tip

05 DSC_6207 2.jpg

A view of a more recent sky tip, in the foreground is part of the mechanism for raising the skips up the incline

  • Steam engines were often used to raise the skips and several engine houses survive, some with the remains of their steam engines and equipment
06 DBD_3301 2.jpg

The remains of a horizontal steam engine at the base of a tip

07 DBD_3312 2.jpg

The Cornish boiler also survives, though it now rests downhill from its original location

07.1 DSC_6512 2.jpg

The remains of a very similar winding engine survive in better condition, the boiler has been removed to Lelant engine house

08 DBD_3364 2.jpg

A rather complete winding drum sits on a concrete base the rest of the engine has been cut up for scrap but why they left the drum I don’t know. If only there were more places like this...

09 DBD_3413 2.jpg

10 DBD_7412 2.jpg

This is how it would have looked: the winder at the King Edward Museum

10.1 DSC_4026 2.jpg

A smaller winding drum seen from a path at the Wheal Martyn Museum

11 DBD_3382 2.jpg

Another Cornish boiler, note the sand in between the inner and outer sections, presumably to insulate it

  • The clay slurry was pumped to the processing area via a steam engine or water wheel from a shaft connected to the pit
Steam pumping engines

A single beam engine has thankfully been preserved near St. Dennis and is now the only complete steam engine surviving in its house of the dozens which were built in the area. I believe there are four other surviving beam engines from clay works which have been removed from their houses. This was a permission visit and the engine house is now in the middle of a modern clay plant.

11.1 DSC_4634 2.jpg

External view, showing the tall engine house with the beam on the left, the winder house in the foreground and the boiler house to the right of the engine house with the chimney hidden behind the trees.

11.2 DSC_4650 2.jpg

The top floor of the engine house, showing the beam built by Sandys Vivian & Co. Hayle in 1852. The engine first worked at a tin mine in St. Agnes before being taken here in 1912. As the tin and copper mines declined many of their steam engines found their way to various clay works. This was one of the last engines working in the area, in use until 1953

11.3 DSC_4585.jpg

The complete Lancashire boiler built by H. & T. Danks Ltd, Netherton, near Dudley

11.4 DSC_4618 2.jpg

The interior of the winder house

14 DSC_8862 2.jpg

This ruined beam engine house is fenced but the shaft is open and unfenced!

15 DSC_2730 2.jpg

This 1915 engine house still retains its original roof although the brick chimney and surrounding buildings have long gone. The engine was replaced by electric pumps in 1944 and put in store at the Science Museum

16 DBD_3836 2.jpg

Another more recent engine house with Cornwall's best-known sky tip behind. Between the two is vast, abandoned pit

12 DBD_3347 2.jpg

A shaft containing the rising main (iron pipe) and pump rod still in-situ, surrounded by a dodgy fence in dense undergrowth

13 DSC_0418 2.jpg

Another rising main, marking the location of a very blocked shaft


Waterwheels

Water wheels were once common on many clay works as a cheaper alternative to steam pumping engines. Waterwheels were especially common on the Bodmin Moor pits where there are only two recorded engine houses.

17 DSC_4344 2.jpg

The preserved 35ft waterwheel at Wheal Martyn was used to pump water from a pit some distance away by means of reciprocating iron rods known as flat rods, seen at the centre of the wheel. To the right of the wheel is a balance bob, used to reduce the reduce the work of the wheel. At the nearest end is the counterweight, filled with stones. There is also a preserved 15ft wheel, also used for pumping

18 DSC_4497 2.jpg

The wheel pit and support for the launder for a 50ft wheel used to pump from a pit one and a quarter miles via a system of flat rods over Bodmin Moor. This wasn’t particularly successful, so a generator house was later built to replace the rods. The wheel was removed in the 1960s to a mining museum in Wales, leaving the very deep pit.

18.1 DBD_4833 2.jpg

Part of a balance bob near the remains of a waterwheel. When I first visited I found the broken remains of the wheel buried under rocks but now a new track has buried it completely with the balance bob just below the dumped material

  • The clay slurry was pumped from the pit to be possessed, first by drags used to remove the mica using long, gently sloping channels to catch the solid waste at the bottom while the clay slowed down.
18.9 DSC_4408 2.jpg

Preserved mica drags at Wheal Martyn, to the right are a series of settling pits

19 DSC_4326 2.jpg

Mica drags in mature woodland in Bodmin Moor from a works which was abandoned over 100 years ago


more to come...
 
Last edited:

featherweight

28DL Full Member
28DL Full Member
really interesting write up td, do you think there will ever be any plans to remove those scree piles? used to live down in Cornwall and always knew I was almost home when I drove past those
 

Terminal Decline

28DL Regular User
Regular User
20 DSC_2615 2.jpg

Leaver used to regulate the water in a set of mica drags

  • The clay slurry was then deposited in circular settling pits, usually near the clay dry
This was the first stage of the dewatering process. The water would be run off, using button-launder where wooden bungs were removed as the clay settled and the water rose to the surface.

21 DBD_3827 2.jpg

Granite steps leading into an early settling pit with part of the sluice mechanism leaning against the wall

22 DBD_9086 2.jpg

One of the two very finely constructed settling pits survive in very good condition along with the sluice, leading to the settling tanks

23 DBD_3782 2.jpg

A very circular large settling pit disappearing into the vegetation- this works closed in 1942

24 DSC_4478 2.jpg

An inverted cone settling pit, begun in 1925 and taking two years to complete! and when constructed, regarded as the advanced and efficient refinery in the area


  • The clay was then released into the settling tanks before being dried in the pan-kiln
After processing to remove waste materials and the dewatering had begun the clay was taken to the pan kiln or dry, often located away from the pits near railway lines. This is basically a long barn-like structure with a furnace at one end and a chimney at the other. hot air from the furnace travelled through a series of flues beneath a tiles floor, echoing the Roman hypocausts. After the clay was dried, it was stored in the Linhay before being removed, often by rail. There are around 100 pan-kilns in the St. Austell area, in varying conditions with a few others around Bodmin Moor and Penwith.

Up to the 1840s, clay was dried in air dies using the natural circulation of air. This would take months and new methods were needed to dry the clay to increase production. The first pan-kilns constructed in 1845 at Greensplatt and Parkandillack following the design of the Staffordshire slip-kilns used to dry flint. The chimney and some walls of the Parkandillack kiln survived into the 70s before being obliterated to construct modern dries.

24.9 DSC_2807 2.jpg

The front of a late pan-kiln with an unusual square chimney dated 1929

25 DSC_5789 2.jpg

Settling tanks at the rear of a kiln, out of the photo on the left

26 DSC_0898 2.jpg

The settling tanks at Wenford dries, on Bodmin Moor with the kilns behind


The filter press house

The introduction of the filter press in 1911 reduced the water content even further by passing the slurry, under pressure through a series of fine cotton filters, forming ‘cakes’.

27 DSC_3084 2.jpg

A blockwork filter press attached to the rear of an older kiln in one of the settling tanks

28 DSC_9206 2.jpg

The filter press, this is one of a large number at the more modern dries at Par Docks though it is very similar to the older ones, though I haven’t found any complete examples


The furnace room

The furnace room usually contains 1 to 3 fire doors where coal was burned to heat the hypocaust style floor

29 DBD_8977 2.jpg

An early furnace room, the iron doors were cast by W. Visick & Sons, Devoran

30 DSC_4293 2.jpg
Looking into another early furnace beside the Camel Trail near Bodmin Moor

31 DSC_2535 2.jpg

The more recent 1920's furnace room of a now destroyed kiln near Par, showing a single intact (at the time) fire door


Some kilns were later converted to oil fired

32 DSC_8808 2.jpg

An oil-fired pan kiln near Par showing the feeding equipment

33 DBD_5131 2.jpg

Looking the other way in another oil-fired kiln


The pan
This was where the clay was dried on a heated floor

34 DSC_1127 2.jpg

Inside one of the more intact pan kilns at Wenford, the floor tiles have been removed, exposing the flues beneath. To the right is the linhay

35 DSC_3897 2.jpg

Brambles pouring into the pan

36 DSC_2732 2.jpg

Most pan-kilns were built on a slope to maximise the amount of clay which could be stored in the linhay. However, this kiln was built on flat ground, the flues and floor tiles have been removed



The travelling bridge

This was a common feature on the larger kilns and was mounted on rails, allowing it to travel the length of the kiln. It allowed carts, either straight from the settling tanks or loaded with pressed clay from a filter press to distribute their load anywhere along the kiln floor

36.9 DSC_4372 2.jpg

The travelling bridge in the pan kiln at Wheal Martyn. The doorway on the left leads to a settling tank and tracks would have been laid to allow workers to easily load the cart and distribute its load on the pan floor

37 DSC_0271 2.jpg

A travelling bridge, showing the rails for the cart and the wheels allowing the bridge to move


The linhay

After the clay was solidified, it was stored in the Linhay before being removed by road or rail. Most linhays were built at a lower level to the pan to increase storage capacity

38 DSC_1061 2.jpg

One of the linhays at Wenford dries which had its own railway sidings

39 DBD_4887 2.jpg

An unusual linhay, built in the 1920s as an independent structure. Note the gulley in the floor for a cart, wooden boards would have covered this over when the building was filled with clay. As the process of removal began, the dry clay was shovelled into the cart which was tipped out into the railway wagons and as the pile of clay receded, the wooden boards were removed.

40 DSC_2148 2.jpg

At this late pan kiln of mass concrete construction, wooden shoots were used to tip the clay into the railway wagons from an unusually great height. This was the most intact shoot, with only the iron ties remaining of the others. Very similar shoots were used at Charlestown to load clay directly into the hold of ships and one of these remains.

41 DSC_1123 2.jpg

Railway tracks hidden in vegetation at the front of a dry

42 DSC_2723 2.jpg

The finest surviving pan-kiln chimney in the St. Austell area. Dating from the 1870s, it had a cut granite base (two thirds of the height) with a brick cap. Many chimneys have been reduced in height over the years making this stack all the more important.



Brickworks

There were once seven brickworks in the St. Austell area and a much larger works at Lee Moor. Bricks made from china clay were exceptionally heat-resistant and therefore were widely used in the mining industry. With the birth of the pan-kiln, a further demand was created as tiles were needed for the heated floor.

43 DSC_3444 2.jpg

The most intact of the three preserved beehive brick kilns at Carbis Brickworks together with the square chimney

44 DSC_3258 2.jpg

A chimney engulfed by waste material and lost in the trees at the last working brickworks in the area. The area was largely buried in sand in the 1990s

45 DSC_3280 2.jpg

Part of one of the two square chimneys at the same brickworks


China Stone

China stone is granite which has only been partly affected by kaolinization process and once crushed, was used as a glaze or could be mixed with china clay to produce high grade porcelain. China stone was quarried like any other rock and then crushed before being ground to a fine powder in china stone mills

46 DSC_5482 2.jpg

A china stone quarry near Nanpean. The last quarries closed in the 1990s and are now being filled with waste material

The china stone mill

Most china stone mills were built with a central waterwheel, flanked by a mill building on either side. Horizontal shafts, driven by the wheel run through tunnels under the floor and bevel gears were used to convert the power into a vertical motion which would drive the iron arms in the grinding pans, turning the crushed stone to powder.

46.9 IMG_20180907_195911.jpg

Plan of a china stone mill
 
Last edited:

Terminal Decline

28DL Regular User
Regular User
47 DBD_3674 2.jpg

A china stone mill showing the waterwheel in the center and mill buildings on either side

48 DBD_3587 2.jpg

Bevel gears below the grinding pans in a china stone mill

49 DBD_3555 2.jpg

Granite grinding pans, held together with iron straps, containing the iron arms used to break up the stone



Post-war china clay extraction process:


Mechanisation began following the Second World War due to the rising costs of coal and a need to streamline production, now effectively in the hands of a single company. Production was concentrated to fewer but much larger pits, swallowing everything in their path. Since Imerys has controlled the industry, many works have been closed and earlier machinery replaced by new methods of drying the clay.

The process I have shown here is not a complete account of the newer methods as many sites have been destroyed before I got the chance to visit them and methods are much more complex, so I’ll just give an overview.


  • The clay pit
50 DSC_1437 2.jpg

Looking down into a vast modern pit on an unusually calm day. It is very hard to show the scale of this working but the top of the access road in the centre is around 800m away!

  • Pumping the clay slurry
51 DBD_3846 2.jpg

A rail mounted pump house on a steep incline at the side of a pit

  • Removal of waste
Conveyors leading to dumps far away from the pit, off the clay ground replaced the sky tip and incline

52 DSC_5943 2.jpg

Looking down a conveyor, leading down into a pit

52.1 DSC_4731 2.jpg

A modern in-use waste tip. In the distance the tip is being covered by soil before being planted to give it a ‘natural’ appearance


  • Refining tanks
53 DSC_6562 2.jpg

The radiating arms at the bottom of the tank push the settled clay to an outlet in the center of the tanks

  • Hydroclones
Hydroclones are used to remove fine mica. The clay slurry enters the top of the cones and coarse particles are discharged to the bottom while finer clay particles overflow at the very top

54 DBD_4758 2.jpg

Hydroclones inside a refinery

  • The centrifuge
This is used to separate fine clays, used in the manufacture of paper. Clay is pumped into a circular, tapered bowl and rotated at high speed and the coarser particles move to the edge as they are more effected by centrifugal forces.

55 DBD_4781 2.jpg

Centrifuges with their casing removed, exposing the rotating bowl inside a clay refinery

  • Filter presses
These can either be square-plate as used in the pan-kilns or the more modern circular-plate

56 DBD_5349 2.jpg

A group of square-plate filter presses at Par Docks. After pressing the clay was discharged from the presses by hand and dropped below to the conveyors, leading to the dryer


  • The Rotary dryer
Rotary dries were the first mechanical drier to be used in the industry and is very similar to the kilns still in use at cement work. A number of these were installed in pan-kilns, making use of the filter presses and linhay. As far as I am aware no complete rotary dries survive at any clay works

57 DSC_7077 2.jpg

A building once containing two rotary dryers. The holes in the floor would have once been taken up by filer presses

58 DSC_6885 2.jpg

Another view of the same building. The dried clay would have been discharged at the very far end of the building and taken to the linhays via the conveyor belt shown


  • The Buell dryer
This was another method of drying the clay which consists of a stack of trays, rotated in a current of hot air inside a circular tower. The clay is fed in the top of the dryer and as a tray completes a revolution, it is pushed off onto the tray below.

59 DSC_4469 2.jpg

An early brick-built buell dryer, one of two intact at Marsh Mills in Plymouth

60 DBD_1210 2.jpg

Looking up at the trays inside a buell dryer at Marsh Mills


  • The linhay
Modern linhays are huge structures where clay is taken by conveyor belt to the top of the roof before being discharged.

61 DBD_1118 2.jpg

A partition inside a modern linhay at Marsh Mills

62 DSC_7259 2.jpg

Silos used to store the clay, one accessed by a conveyor. These were not successful as clay wouldn’t flow freely through them




I have tried to describe the process of extracting and refining as simply as possible while trying to include all the steps taken before the clay is ready to be used in a wide range of products. I still need to visit several other sites, but I feel this report has shown virtually all the traditional processing and a good deal of the more modern methods which I will try and describe further in later reports on individual places. This report has taken me ages to produce and I have used a few diagrams from Cornwall’s china clay heritage which gives a good history of the evolution of clay extraction. I have also included several my photos from Wheal Martyn Museum near St. Austell where a clay works has been very well preserved.


Thanks for looking

61 DBD_1118 2.jpg
 
Last edited:

Terminal Decline

28DL Regular User
Regular User
really interesting write up td, do you think there will ever be any plans to remove those scree piles? used to live down in Cornwall and always knew I was almost home when I drove past those
I'd say most of the remaining sky tips are safe for now as they tend to be around the old disused workings.
There are still a huge number of pristine tips out there in other countries, especially at the coal mines around Donetsk in eastern Ukraine- they are EVERYWHERE! I've put a link below to Google Maps where I've spent way too long looking at the hundreds of collieries in the area which I'd love to try and get to visit one day...
https://www.google.com/maps/@47.9596103,37.5970904,2032m/data=!3m1!1e3

then there is this brilliant website which has some cracking photos of the mines
https://www.viktormacha.com/galerie/donetsk-coal-basin-donbass-270/
 

Jane Doe

28DL Full Member
28DL Full Member
ive always struggled trying to understand how things work but your report is brilliant and with the photos i think i can understand it now :thumb
 

Similar threads


Top