Data is recovered from a write-once optical disk having data written on it. The disk is composed of a substrate and a dye layer. The data was originally written to the dye layer as patterns of pits and lands, but the dye layer is subject to corruption due to ageing so that the data cannot be read by a conventional read process. The data is recovered by exposing the surface of the substrate, measuring deformations to that layer caused by the write process, and extracting the data from the measured deformations by classifying the measured deformations into deformations typical of predetermined patterns of pits and lands.