A long history of kiln firing

Clay Technology magazine
,
18 Aug 2017

Adrian Blundell looks back at the history of the ceramic tile manufacturer, Craven Dunnill Jackfield.

Since Craven Dunnill & Co’s formation, the company has continually invested in new approaches to production by embracing new technology. This was fundamental in the decision to develop its own purpose-built tile factory at Jackfield in Ironbridge Gorge, Shropshire, UK.

This Victorian tile factory, completed in 1874, employed new linear production processes, with new raw materials such as clay, coal, china clay and glaze colours, soon making their way through the factory’s gates. They passed through a series of production process buildings – clay arcs, blunging rooms, clay grinding mills, cake drying floors, colour mills and pressrooms – before the finished product left the site to be sold and distributed worldwide. 

The company invested in new approaches in material handling and processing, spearheaded by Henry Powell Dunnill, who called on the expertise of the architect Charles Lynam, known for designing three of the largest purpose-built Victorian tile factories in the UK – Minton Hollins, Craven Dunnill & Co and Maw & Co – the latter two both at Jackfield. 

Lynam’s early designs for hospitals were largely based upon the idea of segregation of use, with ideas originating from the anti-pauper system for workhouse building design. The same concepts were evident in his later work designing tile factories, in which he established coherent links between use, movement and isolation. These are fundamental to material handling in clay production. The Jackfield site had been associated with ceramic production since 1545, and by 1872 it was long and narrow in layout, confined by coal mines and clay adits on one side and vital transport links of rail, road and the River Severn, on the other. Lynam created the first continuous production line. Buildings and process were linked with few out-of-sight, dead spaces, which led to greater control of workers, materials and product. 

Bottle updraft kilns 

Between 1872–74, the company installed three bottle top updraft biscuit kilns and a larger updraft glost (glaze) kiln, where loading and unloading was via a door, which was bricked during firing. These four kilns were located side-by-side, each within a square structure. A long narrow passage lay along the full length of the kilns, where saggars were loaded and unloaded. Beyond this was another larger area where pressed tiles, biscuit and glazed tiles were sorted prior to progressing onto the next process.   

Although this was the most recent tile-making technology, the kiln design produced wide variations in firing temperatures across the kiln, as the heat passed up and out through the top of the kiln, affecting both the finished colour and size of wares. A typical biscuit temperature is around 1,100°C and glost at 1,000°C, with the whole firing process typically taking two weeks from cold to cold.

By 1895, the original updraught kilns were replaced because of improvements in kiln technology with the latest downdraught kilns, producing an even, efficient and consistent firing condition while reducing production time. The main improvement was that heat from the stoking pits, situated evenly around the circular firing chamber, travelled to the firing chamber’s apex and was then drawn back down through the ware. The heat then exited the kiln through vents and connecting flues in the floor, which led outside of the kiln chamber to a tall square chimney, situated next to the kiln, providing the draw for the hot gases. The airflow through the kilns was controlled using hand-operated paddles known as metal dampers. The base of the external chimney is still in-situ at Jackfield and some of the downdraught kiln hearths can still be seen today.

Prior to the First World War, business at Craven Dunnill was booming, as was the economy. Like other prominent industrialists of the time, Henry Dunnill was known for his liberal and philanthropic thinking. However, this golden period was cut short by the war. Tiles lost their uniqueness and became utilitarian and cheap, while the introduction of gas and electricity transformed production. The Craven Dunnill works became outdated and required new investment.

Improving speed  

In 1930, a coal gas-fired tunnel kiln was purchased from Gibbons Brothers of Dudley after the 1930s Coal Mines Act, which rationalised collieries and regulated coal production. It comprised two large stoking pits and a furnace, located some three metres below ground level. Coal gas is a gaseous mixture, comprising mainly hydrogen, methane and carbon monoxide and formed by the destructive distillation (heating in the absence of air) of bituminous coal and used as a fuel. The yield of gas could be increased by the addition of steam to the hot coke.

The kiln was designed to separate the contaminating combusting coal gases from the ware. This was done using a double skin wall construction, allowing combustion to happen around the inner firing chamber containing the ware, without coming into direct contact with it. Heat radiated through the inner wall, firing the ware to its precise temperature, allowing it to be fired without the use of protective saggars. The process improved the speed and consistency of fired products, while the kiln was controlled using dampers to either decrease or increase airflow through the combustion chamber.

Despite the new technology, the tunnel kiln was taken out of service within a decade, following the ‘Great Slump’ and severe economic downturn. Production finally ceased at the Jackfield factory in the 1950s, and Craven Dunnill moved into tile distribution, working out of premises at Bridgnorth. However, in 2000, after a production break of 50 years, Craven Dunnill once again started manufacturing, at the original factory site.

Current tiling trends

The company continues to use new purpose-built gas and electric intermittent kilns, fabricated in the latest metal, fibre and brick construction. The new kilns have halved the firing times and reduced power consumption. Today, Craven Dunnill Jackfield specialises in the production of historically accurate tiles for restoration projects − both wall and floor tiles for internal and external locations. The role call of prestigious projects completed in recent years is extensive. Public restoration projects are numerous, from The Palace of Westminster and London Underground, which are ongoing, to Oldham Town Hall, Kew Gardens, Leeds Library and several churches, cathedrals and theatres.

The Leeds Library required more than 15,000 handmade tiles in 46 different designs and varieties of colour for the renovation of its Victorian reading room in fitting with its 1950s heritage. New moulds for each pattern were carved, blocks made and tiles cast in special clay bodies, followed by hand-dipping in glazes to reflect the myriad of hues the original tiles had taken on over time. 

A recent trend for designers is featuring faïence tiled walls in hospitality venues, which has led to projects for restaurants and bars in London. The Blues Kitchen in Brixton features a 10m-long handmade faïence tiled bar using five different designs of tiles, dating back to the 1880s. The tiles were made onsite at Craven Dunnill Jackfield using hand carved plaster moulds and decorated using metal oxide glazes, which craze upon firing to create an authentic-aged effect. The tile makers then moulded external corner fittings to allow the highly decorative and ornate patterning to fit around the external corner of the bar front. Mural work also includes the development of two vast, contemporary-based murals for the 2012 London Olympics, which are located in the Queen Elizabeth Olympic Park. 

Today, more than 143 years since it was first established, Craven Dunnill Jackfield continues to make history, winning awards and acclaim for its unique ceramic expertise and bespoke tile manufacturing.

Adrian Blundell is Production Director of Craven Dunnill Jackfield & Co Ltd, a tile manufacturer, formerly known in 1863 as Hawes & Co, in 1867 Hargreaves & Craven and then Craven Dunnill Jackfield & Co in 1870, which was formed on 9 February 1872, by Henry Powell Dunnill.