A substrate (33) is clamped into a fixture (32) and material is deposited thereon to form a complex article (40). The article (40) produced is packed, using ceramic inserts (42) and a coating (41). The packing (42) ensures that the article (40) maintains its true shape and allows for expansion during the subsequent heat treatment process. The packed article (40), mounted on the fixture (32), is then placed in a box (44), encased in a granular material (43) and heated. It is heated to a temperature sufficient to relieve stresses and is maintained at this temperature for a time period such that the stresses in the article (40) are relieved.