34 CONTEXT 177 : SEPTEMBER 2023 production. The use of iron in the construction of glass frames had been advocated earlier by the French botanist Michel Adanson in his Familles des Plantes (1763), for the slenderness of structural iron members in relation to their relative strength when compared, for example, with timber. Rather than wrought by hand on a forge, Loudon conceived of a glazing bar manufactured in a single piece by means of passing hot malleable wrought-iron through rollers. The first examples were produced with the expertise and skill of a foundry in London, W and D Bailey of 272 Holborn. Loudon soon afterwards passed the rights of the invention to William Bailey, who entered a patent in 1818 entitled ‘Windows & C’, No 4277, for the wrought-iron glazing bar. In a letter read to a meeting of the Horticultural Society of London in 1815 ‘On the Form which the Glass of a Forcing-house ought to have’, Sir George Mackenzie proposed the adoption of a quarter sphere as the optimum form for the glass roof of a hothouse, a portion of which sometime throughout the day would be perpendicular to the rays of the sun. Loudon and others, recognised that the strength of the sun’s rays was limited during the early and late hours of the day and throughout much of the day during winter months, They therefore suggested that principles published by the Dutch botanist Herman Boerhaave in 1732 in Elementa chemiae should be adjusted to account for the strength and heat of the sun’s rays at different times of the day and in different seasons of the year, and that consideration should be given to the proximity of plants being cultivated to the surface of the glass itself. Loudon preferred an elliptical or the segment of an elliptical form, where the sun’s rays would be perpendicular to the glass surface during the middle hours of the day in the spring and summer months when the sun was strongest. Following the production of the wrought-iron glazing bar, several early examples were erected by the Baileys of Holborn and others. At the same time patents for ‘metallic’ hothouses with glazing bars made of copper were developed by specialist manufacturers in Birmingham, an important centre for metal trades. Urgent repairs to the greenhouse at Felton Park were undertaken by previous owners of Felton Park in the 1990s, with the support of the north-east region of English Heritage. In 2008 the greenhouse at Felton Park was included in the region’s buildings at risk register, and in 2013 the archaeologist Harry Beamish was commissioned by English Heritage to write a report identifying the significance of the greenhouse that established its rarity and importance.² At the same time English Heritage published a technical report by Vanessa Castagnino on the chemical analysis of the greenhouse glass.³ In 2014 trial repairs to the greenhouse were undertaken to learn more about the condition of the structure, determining the best methods to adopt for its full repair. The following year an extensive repair programme of the greenhouse, and of the bothy standing behind it, was undertaken by the owner Tim Maxwell and led by Robin Dower of Spence Dower Architects, with the aid and support of English Heritage, the Heritage Lottery Fund, the Country Houses Foundation and Northumberland County Council. Tim Maxwell commissioned Alan Fentiman to make a film about the restoration of the greenhouse and has created a website explaining the project.⁴ The conservation repair is the subject of a detailed illustrated report by Robin Dower.⁵ Calibre Metalwork was the main contractor and metalwork specialist, and Cheshire Stained Glass was the glazier. Edward Diestelkamp teaches for NYU London in the MA programme historical and sustainable architecture. The vertical sashes seen from the interior ² Beamish, H (2016) The nineteenth-century, curvilinear lean-to glasshouse range at Felton Park, Felton, Northumberland. ³ Castagnino, V (2013) ‘Felton Park Hall Greenhouse, Felton, Northumberland, Chemical Analysis of Window Glass, Technology Report’, English Heritage Research Report Series, No 5-2013. ⁴ Fentiman, A ‘Felton Park Greenhouse Restoration’ video at www. feltonparkgreenhouse. org ⁵ Dower, R (2017) ‘Conservation of a rare nineteenthcentury iron-framed curvilinear glasshouse’, Journal of Architectural Conservation, March.
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