Late antiquity and Byzantine era Sometime after the Parthenon was converted to a Christian church in the 6th-century CE, the metopes of the north, west and east facades of the Parthenon were defaced by Christians in order to remove images of pagan deities. The damage was so extensive that the images on the affected metopes often can't be confidently identified.
Venetians The Venetian bombardment of the Parthenon in 1687 seriously damaged the majority of sculptures, including some of those later removed by Elgin. Further damage to the Parthenon's artwork occurred when the Venetian general
Francesco Morosini attempted to remove some of the larger sculptures. During the operation, a sculpture of Poseidon and two horses of
Athena's chariot fell and broke into pieces. Several sculptures and fragments were removed by the Venetians.
Elgin Elgin consulted with Italian sculptor
Antonio Canova in 1803 about how best to restore the marbles. Canova was considered by some to be the world's best sculptural restorer of the time; Elgin wrote that Canova declined to work on the marbles for fear of damaging them further. One shipload of marbles on board the British brig
Mentor was caught in a storm off
Cape Matapan in southern Greece and sank near
Kythera, but was salvaged at the Earl's personal expense; it took two years to bring them to the surface.
British Museum The artefacts held in London suffered from 19th-century pollution which persisted until the mid-20th century and have suffered irreparable damage by previous cleaning methods employed by British Museum staff. As early as 1838, scientist
Michael Faraday was asked to provide a solution to the problem of the deteriorating surface of the marbles. The outcome is described in the following excerpt from the letter he sent to Henry Milman, a commissioner for the
National Gallery. The marbles generally were very dirty ... from a deposit of dust and soot. ... I found the body of the marble beneath the surface white. ... The application of water, applied by a sponge or soft cloth, removed the coarsest dirt. ... The use of fine, gritty powder, with the water and rubbing, though it more quickly removed the upper dirt, left much embedded in the cellular surface of the marble. I then applied alkalies, both carbonated and caustic; these quickened the loosening of the surface dirt ... but they fell far short of restoring the marble surface to its proper hue and state of cleanliness. I finally used dilute nitric acid, and even this failed. ... The examination has made me despair of the possibility of presenting the marbles in the British Museum in that state of purity and whiteness which they originally possessed. A further effort to clean the marbles ensued in 1858.
Richard Westmacott, who was appointed superintendent of the "moving and cleaning the sculptures" in 1857, in a letter approved by the British Museum Standing Committee on 13 March 1858 concluded I think it my duty to say that some of the works are much damaged by ignorant or careless moulding – with oil and lard – and by restorations in wax and resin. These mistakes have caused discolouration. I shall endeavour to remedy this without, however, having recourse to any composition that can injure the surface of the marble. Yet another
effort to clean the marbles occurred in 1937–1938. This time the incentive was provided by the construction of a new Gallery to house the collection. The Pentelic marble mined from
Mount Pentelicus north of Athens, from which the sculptures are made, naturally acquires a tan colour similar to honey when exposed to air; this colouring is often known as the marble's "patina" but
Lord Duveen, who financed the whole undertaking, acting under the misconception that the marbles were originally white probably arranged for the team of masons working in the project to remove discolouration from some of the sculptures. The tools used were seven scrapers, one chisel and a piece of
carborundum stone. They are now deposited in the British Museum's Department of Preservation. The cleaning process scraped away some of the detailed tone of many carvings. According to
Harold Plenderleith, the surface removed in some places may have been as much as . On another occasion, it was said that "the damage had been exaggerated for political reasons" and that "the Greeks were guilty of excessive cleaning of the marbles before they were brought to Britain." In a newspaper article, American archaeologist
Dorothy King wrote that techniques similar to those used in 1937–1938 were applied by Greeks as well in more recent decades than the British, and maintained that Italians still find them acceptable. The British Museum said that a similar cleaning of the
Temple of Hephaestus in the
Athenian Agora was carried out by the conservation team of the
American School of Classical Studies at Athens in 1953 using steel chisels and brass wire. Studies of the surface of the sculptures with archaeometric techniques, including Visible-Induced Luminescence (VIL), have revealed multiple traces of ancient polychromy on the sculptures, corroborating the idea that the cleaning damage was less extensive than previously thought. Documents released by the British Museum under the
Freedom of Information Act revealed that a series of minor accidents, thefts and acts of vandalism by visitors have inflicted further damage to the sculptures. This includes an incident in 1961 when two schoolboys knocked off a part of a
centaur's leg, and in 1966 four shallow lines were scratched on the back of one of the figures by vandals. In 1970, letters were scratched on to the upper right thigh of another figure. Four years later, the dowel hole in a centaur's hoof was damaged by thieves trying to extract pieces of lead. In June 1981, a west pediment figure was slightly chipped by a falling glass skylight. ==Return controversy==