Bruxelles, Bibliothèque Royale, Ms. 5557
This mass is doubtfully ascribed to “Ockam” in the source. In Vatican, Capella Sistina Ms. 51 there is an ascription to “Cornelius Heyns” who does not appear in any other musical source. Apart from the shaky ascriptions this mass is quite outstanding. Stylistic features place it around 1460. It is an early example of a mass based on a secular tenor which is treated in the most remarkable technical ways, augmented, reversed, mirrored…. More importantly, the mass has its unique treatment of harmonies and treats these not as accidental to the counterpoint but as a feature of its own right.
The theme of the chanson on whose tenor the mass is constructed is that of bad fortune and labour. But the labour is fun! This might be a hint to the “labours” of the tenor.