Regularly reaching seven figure sums, the 'Strads' are the pinnacle of the stringed instrument world. This 1721 'Lady Blunt' Stradivarius violin was sold by the Nippon Music Foundation, which used the proceeds to aid victims of Japan's 2011 earthquake and tsunami. In 2011, a Stradivarius violin sold for a record $15.9 million (£11.8 million). The instruments are extremely valuable and can often sell for millions of pounds. It was once claimed that Stradivari used wood from old churches to make his famous violins. They said the resultant colder winters and cooler summers slowed tree growth, which in turn led to denser wood with superior acoustical properties. In 2003, US researchers claimed that reduced solar activity in the 17th Century may be the reason for the Stradivarius sound. He was commissioned to make instruments by King James II and King Charles III of Spain. Stradivari is estimated to have produced 1,116 instruments, of which 960 were violins, with around 500 violins surviving to the present day. The violins were made by Stradivari and his family during the 17th and 18th centuries. Violins built by Antonio Stradivari are considered some of the best acoustic instruments ever made. 'Both Stradivari and Guarneri would have wanted to treat their violins to prevent worms from eating away the wood because worm infestations were very widespread at that time.' 'The presence of these chemicals all points to collaboration between the violin makers and the local drugstore and druggist at the time. One chemical used, Borax, 'has a long history as a preservative, going back to the ancient Egyptians, who used it in mummification and later as an insecticide. This treatment, he continued - thought to have been a necessary measure to combat a worm problem at the time - 'had a direct role in creating the great sound of the Stradivari and the Guarneri.' 'All of my research over many years has been based on the assumption that the wood of the great masters underwent an aggressive chemical treatment, Professor Nagyvary explained. Involved in the study was biochemist and violin maker Joseph Nagyvary of Texas A&M University, who first argued that the quality of the Stradivari family's violins - and those of some others - had, for the largest part, a chemical origin. The exceptional sounds of Stradivari violins (like that pictured) come from how the instruments were treated with alum, borax, copper, lime water and zinc to fight worms