It is when faced with similarity that we most notice the differences. And rarely does the difference - and, for that matter, the similarities - matter as much as in the case of a Stradivarius violin. Oxford’s Ashmolean Museum has united a remarkable collection of some of them for a two-month exhibition. There, arrayed across a room in cabinets, delicately suspended on wire and supported on small stands, are some of the most brilliant (and valuable) instruments in the world. At a distance, or when comparing mere measurements, they are the familiar form of the violin: so we must look, and most importantly perhaps must listen, more closely.

"It’s as if the tonal world goes from black and white to colour," writes violinist James Ehnes in the exhibition catalogue of playing a Stradivarius. But how, and why, is a source of speculation and of theories both fantastical and prosaic. The mystery is in the wood, in the varnish... But why? The mystery is in the man, it’s as simple as that. Nobody asks where lies the secret behind Michelangelo’s sculptural forms, whether rendered in marble or on paper, limbs looking poised to flex and reach out at any moment. The mystery is in the chisel, the charcoal...absurd of course. It’s perhaps appropriate that the other exhibition of the summer is of 'Master Drawings', including works by such artists as Raphael, Rubens and Michelangelo. Perhaps this should encourage us to ponder such comparisons.  

And yet an instrument is also, maybe most of all, a functional object: in the case of a Strad, a functional object par excellence, one whose form was perfected in the hands of a unsurpassed master. Collect an audio guide on entrance to the exhibition and while admiring the craftsmanship and, in some cases, intricate ornamentation, you can also listen to many of the instruments being played, some of them by their current guardians, whose intimacy with their idiosyncrasies enables each to sing with greatest beauty.

One exception is the ‘Le Messie’ - Messiah - Strad, so called not because of any particular God-like qualities, but because its owner Tarisio was told, after often boasting of his immaculate but rarely-viewed instrument, ‘Your violin is like the Messiah. He is always expected and never seen’. In the best condition of all Strads, it was bequeathed to the Ashmolean on the understanding it is never played, so that at least one Strad reaches future generations in an approximation of original condition (like all Strads, it too has been altered over the years to reflect more modern playing styles). "It is not a good reason for not playing a Strad. But it is a good reason for not playing this one," says exhibition curator Dr Jon Whiteley. It is, after all, one of about 600, and Dr Whiteley’s aim here has been to gather together some of the finest examples - more than 20, including a few instruments other than violins - but also a representation of how Stradivari’s instruments developed throughout his career. 

You can also see some of Stradivari’s tools, wooden moulds and paper patterns, reunited after many centuries with the instruments they created. A complete Stradivarius violin-making kit then, everything you need to create a new one. Except for the master craftsman himself: the mystery is indeed in the man. 

Stradivarius is at the Ashmolean Musuem, Oxford until August 11. For more details, including about events related to the exhibition, visit the Ashmolean website.