Jesse Shirley’s Bone and Flint Mill
During the first part of the 18th century the beneficial use of ground flint and bone was discovered. Flint (i.e. silica, up to 50% of the total) can be added to clay to produce earthenware products, it gives the ware strength, whiteness and prevents shrinkage during firing to make a hard cream product. The problem with grinding flint using the technology of the day was that it produced clouds of dust; the workers quickly died of “Potters Rot” (silicosis of the lungs) and would not undertake the work. Consequently, the wet pan grinding method was developed to reduce harmful dust; this is illustrated at Jesse Shirley’s Bone and Flint Mill.
Cattle bones were found to be the most suitable for adding to clay (again up to 50% of the total) to produce bone china. It is the bone which gives the ware its characteristic translucent quality, it is whiter than other ware and its high strength allows it to be finer.
About 1747 it was discovered that Cornish stone (a partly weathered granite) mixed with china clay would form a porcelain body. Small quantities of Cornish stone were also processed on site.
The two processes for bone and flint were similar and the ground products revolutionised the ceramics industry; existing water powered corn mills were converted and new water mills were built. Wind could not supply the continuous high power required, but steam power was an obvious application as steam engines became more powerful and reliable. Thus building of the steam powered Jesse Shirley’s Mill was commenced in 1856 at the Junction of the Trent and Mersey Canal and the Caldon Canal as canals offered cheap transport of these heavy raw materials.
Flints occur in bands within Cretaceous Chalk beds, they are an unlikely ceramic raw material as they are hard and black in their natural state. However, if they are calcined (roasted) above 1000 degrees centigrade crystalline water is driven off to leave a softer, lighter and whiter product. The calcining kiln consists of two chambers with a hovel built above them to create a draught to aid combustion. Flints would be built up in layers with slack coal, it would be allowed to combust for 8 to 16 hours (depending on the fuel and climatic conditions) and then left to cool before being withdrawn through draw holes at the bottom.
Bone was treated in a similar way after first being boiled to remove tissue, this would produce glue; a saleable by-product. Wood was used as the fuel as bone is prone to contamination from iron pyrites in the coal. Less fuel was required than for flint and combustion was quicker. Again calcined bone is softer and whiter than in its natural state.
This is now entered down steps, but originally the floor was level with the canal wharf outside. Mining subsidence has lowered the whole area by about 6 feet (2 metres) and the canal wharf has had to be raised to maintain the canal level (see the blocked up lower part of the windows in the Gear Room).
Here are the two draw holes for the kiln.
The crusher is of the oscillating jaw type. It is belt driven by a small horizontal steam engine of unknown manufacture and date and was used to crush oversize flints and Cornish stone.
In the middle of the floor is a circular iron turntable plate sitting on rollers, carts wheeled in from outside were turned on here to be pushed into the gear room.
Steam is generated in a ‘Cornish’ boiler built at the nearby Cliffe Vale Boiler Works in 1903. It is hand fired with coal and contains about 2,500 gallons (11,000 litres) of water, the water level is indicated in two water gauge frames and the steam pressure by a Bourdon gauge. The dead weight safety valve releases pressure at 60 pounds per square inch (4.1 bar), although the boiler is operated at less than half that pressure. It is important to maintain the water level in the boiler and new water from a large cast iron tank in the roof was originally pumped in, against boiler pressure, by two Weir steam pumps, examples can be seen against the side wall. Today electric pumps are used.
The ‘Cornish’ boiler was transported from Tunstall Swimming Baths and installed in 1990, the original ‘Lancashire’ boiler (a much larger boiler with two fire tubes compared to the ‘Cornish’ boiler’s one) had been scrapped and the flue to the brick chimney cut off; so a smaller steel chimney was installed. Steam is taken off from the top of the boiler to be brought through a large diameter pipe to the engine room next door.
“Princess” is a double acting condensing rotative beam engine to the design of James Watt. She was installed when the mill was built in 1856, but was second hand, her previous history is unknown, but she was thought to have been built by Bateman and Sherratt of Salford about 1820.
Steam enters the single large vertical cylinder through a main steam valve, steam pressure is directed to either end of the cylinder via valves which are operated by a rocking shaft beneath the floor which is, in turn, operated by an eccentric from the flywheel axle. Exhaust steam is condensed in a condenser beneath the floor, this creates a vacuum which is connected to the cylinder again via the valves, thus the pressure difference between steam pressure on one side and vacuum on the other moves a piston within the cylinder.
The two gauges on the wall show the strength of the vacuum and steam pressure. For the engine to be double acting (i.e. to be able to pull and push); the piston is connected to a rod which emerges from the cylinder head through a ‘metallic’ gland packing, The piston rod must travel in a vertical straight line, but power is transmitted through an overhead beam, as it rocks the end transcribes an arc which would pull the rod backwards and forwards. James Watt overcame this problem with his parallel motion; a trapezoidal connection. At the other end of the beam is the sweep rod which connects via a crank to the axle which carries a flywheel of 20 feet (6.1 metres) in diameter and 10 tons (10.18 tonnes) in weight. The flywheel’s momentum carries the engine over top dead centre and bottom dead centre when the piston is at the end of its stroke and is not providing any power. The axle extends through the wall into the gear room.
Also in the Engine House is an inverted rotative ‘Cameron’ style steam pump, often called a ‘banjo’ pump because of the unusual connecting rod to crank connection which produces an oscillating motion. This was used to pump water out of the flywheel pit, flooding becoming a problem as the building subsided. A modern electric pump now keeps this clear of water.
Power is transmitted via the flywheel axle through a ratchet which enables the engine to be barred backwards by hand if, for example, it has stopped on a dead centre and will not start, without moving any of the machinery backwards. Rim gears transmit the power to long line shafts which run the length of the room (one shaft is currently driven, the other is disconnected). Along each line shaft are five bevel gears which drive vertical shafts taking the power up to the pan room above.
Particles in the ground mix tend to coagulate and must be separated. Thus the mix is brought from the Pan Room through wooden launders to wash tubs. There are three of these and rotating paddles stir the mix, it then ‘blunges’ through the vertical bars of the paddles (or ‘gate’), to separate the particles. A line shaft driven piston pump was used to pump the mix around the system.
Also in this room are two rectangular settling arks, these are small and were for special products, much larger arks holding 25 tons (26.2 tonnes) of liquid were beyond the gear room wall and have been lost during development of the site. As the solid particles settle; wooden bungs in a vertical plank are knocked out to run clear water off. This leaves a thickened slop which could be put into barrels and sold or pumped to drying beds (which have also been lost) where water was evaporated off and the solid product sold as blocks. Above the arks is a ‘Pulsometer’ steam pump. It has two chambers, steam pressure empties one side whilst the vacuum from condensed steam draws fresh liquid into the other side. A steel ball then rocks over a knife edge to allow the process to be repeated on the other side.
Material to be ground was hoisted through a hatchway in the floor from the Gear Room below. The slack chain hoist was driven from the extended vertical shaft of the small end pan. The material was then tipped into one of ten pans and water was added, the pan floor is composed of chert blocks with the gaps filled with ‘pitcher’ (broken biscuit ware). Power from the floor below rotates sweep arms which push large chert blocks or ‘runners’ around the pan. The material is pushed and tumbled around the pan and is ground in the process.
The larger diameter pans contain larger runners of up to one ton in weight and a hand crane at one end of the room was used to lift these into the pans. After about 8 hours for flint, less for bone, the material was ground and could be run out of the pan to the floor below for further processing.
In June 1978 Jim Kelly, then the Keeper of Social History at the City Museum, called for volunteers to restore the Mill and machinery. It had been in continuous use from 1857 until work stopped when modern machinery on site had been commissioned to replace it in 1972. During that time it had seen little alteration, it had become neglected during its latter days, but was essentially as it had been built well over a century before. The first working party took place on 22nd October 1978 and voluntary work has continued to the present day, some of the original volunteers are still on the team over 32 years later.
The site’s historical significance was recognised in 1975 with it being designated a Scheduled Ancient Monument. A replacement boiler was installed in 1990 to provide steam for the engine and the site was officially opened to the public by Fred Dibnah on 6th April, 1991.
The present operator of the company, i.e. Mike Shirley, is actually Jesse Crawford Michael Shirley, the sixth generation of the Shirley family to be involved in the affairs of the Hanley district and the fifth to be directly involved in the Jesse Shirley Company. Every generation has named one son, usually the eldest, “Jesse ……. Shirley”.
Joseph Shirley married Mary, giving birth to Jesse (1) in 1791. In 1811 he married Jane Knight who gave birth to Joseph in 1813 and Jesse (2) in 1819. But Jesse (1) died in 1828 and his widow Jane married John Bourne (1795 to 1852) in 1834 (Jesse (2) referred to John Bourne as his “father”, but strictly meant his step-father or perhaps refers to a close bond between them). Jesse (2) married Sarah Lovatt in 1843 having four sons including Jesse (3) in 1848. His son Jesse Wilfred (4) was born in 1883, he married Annie Crawford who gave birth to Jesse Wilfred Crawford (5) in 1922. He married Margaret Crawford who gave birth to Jesse Crawford Michael (6) in 1954.
Jesse born in 1834 was employed by his step-father John Bourne at his firm of Bourne and Hudson Bone Works originally as a writing clerk. When John Bourne died he left the business to his two step-sons Joseph and Jesse Shirley (2). It was the latter who had the present Mill constructed in 1856/1857.
The road access to the site was poor, but the location was no doubt chosen because of the proximity to the canal.
Bone would originally have been sourced locally, Hanley Meat Market was suggested as a source. But when anthrax became a concern; bone was sourced from overseas with the deglutinisation being carried out there and the risk thus being removed. Latterly bone came in from Southern Ireland, Argentina, Holland, Sweden, Pakistan, India, Egypt and even China. Flint occurs in bands within Cretaceous Chalk strata. These outcrop on the Isle of Wight and south coast and run up to the coast of Lincolnshire and south Yorkshire. As the cliffs are eroded; flints are washed onto the beaches of Norfolk. More recently flints have been obtained from chalk pits in southern England and, when demand was high, from beaches in Belgium and northern France. The ‘chalk’ flints, with their calcium carbonate crusts, were regarded as inferior, with respect to grinding, to the ‘pebble’ flints found on the beaches which have had their crust and rough corners eroded away. However, the ‘chalk’ flints, because of their knobbly nature allowed a better draught in the kiln, were quicker to calcine.
As indicated above, the raw materials were brought to the Mill via the canal network, some of the product went to the potters via horse and cart, but most went along the canal.
Filling the kiln was a very skilled job requiring layering of fuel and either bone or flint. Coal was used to calcine flint, although cheap slack coal could be used for the top layers. About one hundredweight of coal was used per ton of flint. It is said that bone would use wood as the fuel, latterly railway sleepers, as it was easily contaminated by iron pyrites in the coal, and because of its organic nature; bone required little fuel once combustion had commenced.
The time taken to calcine flint would depend on the type of flint, quality of the fuel and climatic conditions, but would take 8 to 16 hours. Bone would be quicker. The calcined product must also be allowed to cool before manual handling; so 24 hours would typically be allowed from cold to cold. The production of ground flint is said to have ceased at the Mill in the 1930s and certainly would have been impossible in the 1960s due to the Health and Safety Regulations which were introduced.
Around the site there would be 12 to 14 men employed. Whilst the work would be arduous, dusty and very smelly; it is apparent that employees might spend most of their working lives there, so it must have been regarded as a good place to work.
Originally the major pottery manufacturers such as Wedgwood and Spode had their own steam engines and grinding pans, the Mill would then have supplied the many hundreds of smaller manufacturers. By the 1960s/1970s the company was supplying most of the bone china factories such as Coalport, Crown Staffordshire, Hammersley China, Royal Stafford, Hall Bros., Regent Works, Taylor and Kent, Rosina China, Aynsley, Royal Doulton and Wedgwood.
At its peak the Mill was producing 80 to 100 tons of product per week. Latterly there were problems with the roof beams dropping below the working arc of the crane which prevented the larger pans being used and production had dropped to about 30 tons per week. A ton of bone would make about 2,500 bone china 10 inch plates or 5,000 cups.
The Mill was decommissioned because of the problems noted in 10, over 10 tons of coal a day was being purchased, mainly for the boiler, and environmental pressures. Also, an expenditure of £20,000 on the latest ball mill technology could produce 30 tons of ground bone per week with just an electricity cost and a workforce just working days as opposed to 24 hours. The mill ceased working in 1972 with the workforce walking out and into the new grinding facility, this left partly ground material in the pans which caused some problems in removing it when restoration commenced in 1978.
The importance of the Mill was recognised by it being designated a Scheduled Ancient Monument in 1975.