<p>Surface processing in which the area to be processed is restricted to a predetermined pattern, can be achieved by: (a) providing a layer of a first reagent over a region of the surface to be processed which at least covers an area of the predetermined pattern; (b) providing one or more further reagents which are further reagents required for the processing of the surface; and (c) applying at least one of the further reagents over the region to be processed according to the predetermined pattern; such that the first reagent acts with the one or more of the further reagents to process the surface only in the area of the predetermined pattern. The process is particularly applicable to etching where an etchant having two or more components is used. In that case at least a first etchant component is applied over the surface and at least one further etchant component is applied in the predetermined pattern.</p>
