Tests being carried out on some of Caravaggios most famous paintings have revealed unexpected secrets regarding the artists materials and techniques. XRF (florescent X-ray) analyses of St. Matthew and the Angel in the Contarelli Chapel in the Church of San Luigi degli Francesi, Rome, have shown that Michaelangelo Merisi (to give him his true name) used ground malachite to create an emerald green background for the altar piece instead of his usual earth brown. This is the only known case to date where the artist used this precious material.

The tests, carried out by the Istituto Centrale per il Restauro (Central Institute of Restoration) and sponsored by the National Caravaggio Committee and the Italian Ministry of Cultural Heritage, are part of the preparations for the celebration of the 4 th Centenary of Merisis death in 2010. The St. Matthew in the Contarelli Chapel is the second version the artist made of the same theme. His first version, which depicted the evangelist as a rough peasant with dirty feet, was turned down by his patrons because it was considered too crude and realistic.  

The painting is flanked by two of the artist other famous masterpieces The Martyrdom of St. Matthew and The Vocation of St. Matthew.