A method of forming a weld between workpieces (1, 2) over a joint region (3). The method comprises: exposing the joint region (3) to incident radiation (4) having a wavelength outside the visible range so as to cause melting of the surface of one or both workpieces at the joint region, and allowing the melted material to cool thereby welding the workpieces together. A radiation absorbing material is provided at the joint region (3) in one of the workpieces (1,2) or between the workpieces which has an absorption band matched to the wavelength of the incident radiation so as to absorb the incident radiation and generate heat for the melting process. The absorption band lies outside the visible range so that the material does not affect the appearance of the joint region (3) or the workpieces (1, 2) in visible light.