The air-drying mechanism of a conventional soya alkyd and of a linseed oil has been investigated by a new technique -- time-lapse infrared spectroscopy. This technique is capable of assessing not only the reactions taking place during polymer cure but when and in which order they occur. Each of these materials was found to follow a similar though different oxidation route. Both are initiated by oxygen via hydroperoxide formation; however, their generation/ decomposition rates and their oxidation and crosslinking paths differed markedly. The observed reactions are compared with some previously reported drying mechanisms. -- AATA