An apparatus for etching a workpiece in which a first abrasive particulate material, for example aluminium oxide, and a second particulate material, for example glass dust, are entrained together in a stream of gas. The apparatus recycles exhaust particulate material by introducing it into said gas stream, the exhaust particulate material including particulate material removed from the workpiece by the action of the gas stream with entrained particulate material. The apparatus is particularly suited for etching toughened glass.