Ornamental Cast Iron

David Mitchell

Iron ore was traditionally smelted in a blast furnace, originally using charcoal then later coke and coal, although peat was used on a limited basis in some areas. Limestone was added as a flux to reduce the temperature at which the ore melted, and to assist the removal of impurities in the form of slag. The resulting iron was run from the base of the furnace or ‘tapped’ and run into open indentations in the ground known as pig beds for their fanciful resemblance to suckling pigs. The pig iron was manageable by hand and could be re-melted in a small cupola furnace* to make castings.

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The castings were originally made in open sand moulds in the ground (sometimes directly from the blast furnace) but, as the industry developed, specialist moulding boxes and moulding sands were introduced. The last remaining architectural iron founders in operation today largely use the same processes as in the 18th and 19th centuries.

The moulder prepared the ‘green sand’, so called because it was used in its raw or ‘green’ state. High quality moulding sand was highly prized, and was largely recycled in the foundry, actually becoming better with use. It contained clay particles among the quartz grains, which were hydrophilic, making it slightly sticky when damp. Fine coal dust was also added throughout the sand, which burned out as the molten metal came into contact with it, helping to take the gases away from the casting and preventing the formation of gas bubbles in the finished product.

A pattern*, usually made of wood, but sometimes of cast iron, lead or plaster, was placed on a board with a box around it, or used as a ‘loose’ pattern (not on a board but resembling the finished casting). The facing sand was finished in plumbago* which was ‘rammed’ or pressed up against the pattern, followed by successive layers of rammed sand. The pattern would then be carefully removed and the process repeated in the other half of the moulding box. When complete, the two sides of the box would be brought together and the molten cast iron taken from the cupola furnace and poured into the mould through pre-formed gates* and risers*. Once cooled, the box would be opened and the casting removed. The excess metal left by the gates and risers would be removed and the casting cleaned up.

Most architectural cast ironwork uses grey iron* for manufacture. Cast irons have varying degrees of ductility*, but all are fairly brittle. Impact resistance is minimal, although the material is excellent in compression and therefore ideal for columns.

THE ORIGINS OF ARCHITECTURAL CAST IRONWORK

Decorative ironwork was largely undertaken in wrought iron until the latter half of the 18th century, when cast iron became increasingly and the demand for mass-production. The evolution of architectural cast ironwork in the 19th century has its stylistic roots firmly embedded in earlier wrought iron forms, and the significant wrought ironwork of smiths such as Jean Tijou in the 17th century had a lasting influence into the 20th century.

During the first decades of the 18th century, cast iron was increasingly used in component form within wrought iron assemblies, as is the case at Chirk Castle near Llangollen, where the entrance gates and piers by the Roberts brothers erected in utilised cast iron in the gate pier bases and pediments alone. However, its use as a standalone medium in railings in particular became increasingly important. The earliest significant example of this is generally considered to be the cast iron railings installed around St Paul’s Cathedral in . Cast at Lamberhurst in Kent, the castings weighed 200 tons.

While Sir Christopher Wren disapproved of the use of cast iron to bound his building, the Arts and Crafts architect William Lethaby later praised them highly: ‘I do not see how the railings could have been better. They are heavy and rather blunt as befits the situation and the material of which they are made’. Some of these railings were removed and sold at auction in , but much of the work still survives, and it is a testament to both the design and the material that they remain in excellent condition. As Lethaby suggested, the design and execution of the ironwork at St Paul’s reflects an advanced understanding and appreciation of the material. The construction is massive, perhaps too much so, but the ironwork is assembled and jointed like carpentry; the joints are tight and neat throughout. James Gibbs used cast iron railings of a similar design for the Senate House in Cambridge in around , but unlike those at St Paul’s, here he utilised wrought iron bars inserted between the railings.

Isaac Ware’s architectural treatise A Complete Body of Architecture published in contains several plates illustrating ironwork in the form of gates and railings. Ware makes comment on the architectural use of cast iron in a decorative context: 'Cast iron is very serviceable to the builder and a vast expense is saved in many cases by using it; in rails and balusters it makes a rich and massy appearance when it has cost very little and when wrought iron, much less substantial, would cost a vast sum'. Indeed, the comparatively low production costs of cast iron compared to the labour intensive costs of wrought iron manufacture are pivotal to the rise of the material in a decorative function.

COALBROOKDALE AND CARRON

Early castings, which were relatively plain and easier to mould and cast, were replaced by increasingly ornamental and stylised designs as the potential of cast iron was realised at Coalbrookdale and then at Carron, through increasingly fine design and pattern work. This would also have required a development in pattern-making and moulding skills, as exemplified by the work of the Haworth brothers at Carron, brought from London to Scotland by the architects Robert and James Adam.

The rise of the Adam brothers was inextricably linked to the rise of the Carron company and of the Scottish ironfounding trade. Early examples of their work used wrought iron often in conjunction with other metals such as copper and brass, but the influence of cast iron gradually appears in their work towards the end of the 18th century. Details such as decorative cast iron finials, usually to classical motifs, were introduced and used in conjunction with wrought iron railings.

A Scottish example of this can be found at the tomb of James Bruce in Larbert Old Church, where remnants of the original railings enclosing the burial site survive. Erected in around , these railings were delicately forged in wrought iron, intersected by a more substantial wrought iron newel post, and topped with a decorative cast iron urn. They are now badly corroding and delaminating, nevertheless, they provide an excellent illustration of the transition period between wrought and cast iron, as the Adam brothers started to use the mass production benefits of cast iron in the finial detail, while retaining delicacy and craftsmanship in the forged bars and cope rails.

The monument to James Bruce was a large cast iron obelisk, which is itself an early Scottish example of the potential of cast iron as a decorative medium for a striking feature. Unfortunately, it has been moved from its original location adjacent to the graveyard where it sat on a masonry plinth where the family remains lie. It can now be found in the church car park, a less than dignified location for such an important monument.

The Adam family became inextricably linked with Carron in the early s when they became shareholders, with John Adam the most prominent in the affairs of the company. The elegance of their designs was carried over to railings and other architectural work.

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The execution of the iron bridge at Coalbrookdale by Abraham Darby and the Coalbrookdale Company in was a significant datum in the use of cast iron as a construction material and as a decorative medium. However, the decorative work that Coalbrookdale was later to become famous for is not particularly evident on the iron bridge. The central panel was cast in an open mould (there is evidence of porosity in the panel and generally across the bridge components). The iron bridge is important less as a decorative expression in architectural ironwork, than as a pivotal statement in the versatility and use of the material.

THE GOLDEN AGE

Significant advances in the technology of smelting and working iron were intertwined with the rise of the material for decorative purposes, its potential so clearly demonstrated by the Adam brothers and Carron in Scotland. The technological advances and natural resources realised in Scotland in the late 17th and early 18th centuries were to create strong foundations for the significant architectural ironfounding industry which was to follow. World-famous names like Walter MacFarlane & Co, Lion Foundry, McDowall Steven & Co and the Sun Foundry of George Smith were established within a 30 mile radius of Glasgow. Coalbrookdale excelled in quality but never matched the range and output of those north of the border.

British firms pre-fabricated cast iron palaces, fountains, bandstands, railway stations and bridges, shipping them to the far reaches of the globe. Specifiers in India or Brazil could order from a stock pattern book, selecting a weathervane or rainwater gutter, a clock tower or urinal. The national output peaked around , although it had really started to accelerate with the drive to improve sanitary facilities starting in the s. While catalogues showed high quality ornamental work, most firms relied on the manufacture of sanitary ware to build their business.

AFTER THE VICTORIANS

The taste for ornamental cast ironwork shifted in the Edwardian period, with most firms responding with more subtle art nouveau stylings. The advent of both wars impacted heavily on the industry, with a loss of customers and skilled labour as foundries shifted towards war work.

The post-war housing boom provided a temporary respite in the manufacture of sanitary ware and baths in particular, but this too was short lived as pressure from overseas imports started to bite. A handful of firms embraced the shift to using cast iron as a constructional medium in building facades, and wonderful examples remain largely unknown in our towns and cities. Selfridges (Oxford Street, London) and Unilever House (Victoria Embankment, London) used large amounts of cast iron, and Burtons the tailors used cast iron extensively in its shop fronts in the post-war period.

After a series of often acrimonious amalgamations and takeovers alongside a general decline saw the sad demise of a once formidable industry. Some smaller firms did survive and, ironically, saw a resurgence of conservation and restoration work in the s re-instating ironwork removed for the war effort or repairing the profusion of Victorian cast ironwork in our public parks. The resurgence was principally driven by the Heritage Lottery Fund Urban Parks Programme. The handful of surviving firms remains under increasing pressure on various fronts. To retain them we need to use them, and to understand and appreciate the high quality that ornamental cast ironwork can achieve.

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Glossary*

Cupola furnace Furnace shaped like a smoke stack Ductility A metal’s ability to retain its strength when its shape is changed Gate The point at which the molten metal enters the mould Grey iron Common type of cast iron in which a high proportion of the carbon is in the form of graphite flakes Pattern ‘Positive’ original used to produce the desired ‘negative’ cavity form inside the mould into which molten metal will be poured Plumbago Powdered graphite Riser Channel in the mould allowing formation of a reservoir of molten metal to compensate for shrinkage as the molten metal solidifies

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Introduction:

In the realm of metalworking, two materials have long held sway for their strength, versatility, and aesthetic appeal: wrought iron and cast iron. While both are revered for their durability and timeless charm, they possess distinct characteristics that set them apart. In this comprehensive blog, we delve into the differences between wrought iron and cast iron, exploring their unique properties, manufacturing processes, and the myriad benefits they offer for various applications.

Understanding Wrought Iron:

Wrought iron, prized for its superior strength and malleability, has been a cornerstone of metalworking for centuries. Unlike cast iron, which is formed by melting and pouring molten metal into molds, wrought iron is forged through a labor-intensive process involving repeated heating, hammering, and shaping. This method of production aligns the iron’s crystalline structure, imparting exceptional tensile strength and ductility. As a result, wrought iron exhibits remarkable resilience and resistance to bending, making it ideal for applications that require both structural integrity and intricate detailing.

The Benefits of Wrought Iron:

Wrought iron’s inherent strength and versatility make it a preferred choice for a wide range of architectural and decorative elements. From ornate gates and fences to elegant stair railings and furniture, wrought iron adds a touch of sophistication and timeless elegance to any setting. Its ability to withstand the elements with minimal maintenance makes it particularly well-suited for outdoor applications, such as garden trellises, balcony railings, and pergolas. Additionally, wrought iron’s adaptability in design allows for endless customization, enabling artisans to create intricate patterns and elaborate motifs that enhance the beauty and character of any space.

Exploring Cast Iron:

Cast iron, renowned for its durability and heat retention properties, has found myriad applications in both industrial and domestic settings. Unlike wrought iron, which is forged from solid metal bars, cast iron is produced by melting pig iron and other scrap metals in a furnace, then pouring the molten metal into molds to form the desired shapes. This casting process results in a material that is dense, rigid, and highly resistant to wear and deformation. Cast iron’s ability to hold intricate details and its uniform composition make it ideal for manufacturing a wide range of products, including cookware, machinery parts, and architectural components.

The Advantages of Cast Iron:

Cast iron’s unique properties make it indispensable for numerous applications where strength, durability, and heat resistance are paramount. In the kitchen, cast iron cookware is prized for its exceptional heat retention and even cooking properties, making it ideal for searing, frying, and baking. In industrial settings, cast iron’s ability to withstand high temperatures and heavy loads makes it an essential material for engine blocks, pipe fittings, and machine bases. Additionally, cast iron’s smooth surface finish and corrosion resistance make it a popular choice for architectural elements such as columns, balusters, and ornamental plaques.

Choosing the Right Material:

When deciding between wrought iron and cast iron for a particular application, several factors must be considered, including the desired aesthetic, functional requirements, and budget constraints. Wrought iron’s unparalleled strength, flexibility, and ornamental appeal make it an excellent choice for decorative elements and structural components where intricate detailing is desired. Cast iron, on the other hand, excels in applications where durability, heat resistance, and uniformity of shape are critical, such as cookware, machinery parts, and industrial fixtures.

Conclusion:

In the timeless debate of wrought iron vs. cast iron, both materials offer unique advantages and charm that have captivated artisans and craftsmen for centuries. Whether adorning a historic mansion, enhancing a modern kitchen, or fortifying an industrial machine, wrought iron and cast iron continue to stand as enduring symbols of craftsmanship, resilience, and timeless elegance. By understanding the differences and benefits of these two venerable materials, designers, architects, and homeowners can make informed decisions that elevate the beauty and functionality of their projects for generations to come.

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