The Building Conservation Directory 2020

154 T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 0 C AT H E D R A L C O MM U N I C AT I O N S ALL THAT GLITTERS… ALEXANDRA MILLER O UR LOVE affair with gold and other shiny things has been a long and interesting one. In 2009, the Staffordshire Hoard, the largest discovery of Anglo-Saxon gold ever found in the UK, captured the attention of the international press. It was such an important find, not just because of the quantity of gold found, but because it showed that immensely technical and hugely complex methods had been used to extract inferior metals from recycled gold alloys. When this took place in the 6th century, this extraordinary task would have represented an immense expenditure of precious resources for an end product with no great practical use or value – apart, of course, for the unrivalled symbolism of power and success. Alongside its use as currency, gold has always been used to adorn the most important religious and royal art, palaces and stately homes, places of worship, mausolea of the rich and powerful, aristocratic attire and fine jewellery. Its preparation from ore to decorative gold leaf and solid bar is such an ancient technique that there is no exact record of when it began, although we know the act of working gold into thin sheets is recorded as far back as ancient Egypt. The use of gold to honour and serve only the very highest of institutions stayed unchallenged until the advent of electroplating in early 19th century Britain. Originally discovered during the relatively mundane investigations into materials to improve the conductivity of electrical cables, gold plating was put to immediate commercial use. WHY GOLD? Chemically speaking, gold is an extraordinary element with many desirable properties. It never tarnishes due to the difficulty oxygen has bonding to its only electron in its outer 6th shell, making any possible chemical bond too weak. This property makes it eternally perfect and is one of the defining reasons it is so highly prized for decoration. It is also highly conductive, even occurring as trace elements in our blood where it helps with conductivity of our heart’s electrical impulses. Gold is non-toxic, which if you know much about the history of most other decorative materials is quite remarkable, and with a melting point of approximately 1,000°C, it has ensured that this material could only be worked by experienced and established goldsmiths, usually with very rich and determined patrons: thus protecting its exclusivity and rarity. Unfortunately, gold is also incredibly rare. It has been estimated that “all the gold ever mined in the history of the human race would fit into a cube about 60ft on edge” (Theodore Gray, The elements, a visual exploration of every known atom in the universe. p181). These attributes have led to highly refined craftsmanship, resulting in the use of the thinnest leaves of gold to cover surfaces and maximise coverage. This technology, which dates back thousands of years to the ancient civilisations in Egypt and China, involves melting the gold or gold alloy and pouring it into flat sheets. When cool and hardened, these sheets would then be cut into small squares and hand beaten to flatten out. Because of gold’s density, the resulting ‘leaves’ of gold still retain their structural integrity at approximately 0.1 micron thick (1/1,000 the thickness of standard printer paper) and can cover a vast area. There is very little physical material in a leaf of gold – most of its value is in the crafting of the leaf. For example, in 1983 just 4.5kg of gold was used to gild the whole roof and all the clock faces of Big Ben (the Elizabeth Tower), an overall surface area of around 18,000 sq ft. Very little can go a very long way. HOW IS GOLD APPLIED? The techniques used by gilders to apply gold leaf to surfaces are, in very basic terms, defined primarily by the type of glue needed to stick the gold to a substrate. The two main types are water based and oil based, known individually as water gilding or oil size gilding (there are many other variations). Where gold is to be used in powder form, various synthetic oil varnishes, resins or natural protein based liquids, such as egg white are used to hold the particles of real gold in suspension, forming genuine gold paint. Regardless of technique, the first step is to apply a waterproof coloured substrate upon which to apply the gold. This is to ensure that the final layer of gold has a solid and even appearance. WATER GILDING Simply put, water gilding is the painting on of water mixed with a little gelatin and alcohol, over a carefully prepared ground of gesso (typically chalk bound with animal skin glue) coated with pigmented clay mixed with rabbit skin glue called ‘bole’. The gilding water activates the glue in this substrate to create a sticky layer which the gold leaf will stick to. Once laid, the gold leaf can be burnished to a high shine using an agate stone. Water-soluble adhesives are generally unsuitable for exterior decoration as the gold leaf is easily damaged by moisture. Water gilding is also not usually found in British interior decoration as it is a very labour intensive process and the high shine would have been found too garish for the prevailing aesthetic of most British decorative periods. However, the technique was widely used on the Continent for furniture and picture frames or as highlights on architectural features such as column capitals, and it may be found in Renaissance and Rococo interiors such as The Palace of Versailles. A close up of plasterwork at the London Coliseum: the metallic finish of the shields is indicative of gold leaf, and is easily distinguished from the brassier colour of the entablature above, which is almost certainly bronze paint. (Photo: Alexandra Miller)