How did they paint the Très Riches Heures?

The Limbourgs used a wide variety of colours obtained from minerals, plants or chemicals and mixed with either arabic or tragacinth gum to provide a binder for the paint. Amongst the more unusual colours they used were vert de flambe, a green obtained from crushed flowers mixed with massicot, and azur d'outreme, an ultramarine made from crushed Middle Eastern lapis-lazuli, used to paint the brilliant blues. (This was, of course, extremely expensive!)

The extremely fine detail which was the characteristic feature of the Limbourgs needed extremely fine brushes and, almost certainly, lenses. Later additions to the Très Riches Heures carried out by the late 15th-century artist Jean Colombe were carried out in a rather less delicate way. The calendars, however, were mostly painted by the Limbourgs; only November includes a substantial amount of Colombe's work.