(57) In a hot isostatic pressing process or hot uniaxial pressing process for producing a net or near net shape product, a diffusion filter comprising boron nitride is provided between a graphite former and metal powder to be pressed there against. The diffusion filter allows a controlled amount of carbon to diffuse into the surface of the pressed component. The boron nitride is conveniently applied as an aqueous slurry by spraying. In order to obtain adherence between the coating and the surfaces of the former, one or more thin ghost coat layers of slurry are applied to the surface of the graphite former before one or more layers of normal strength slurry are applied. Each layer of coating is allowed to dry before the next layer is applied, and the former may be heated to dry each layer. Pressed components of length greater than 2m can be processed, relative contraction of the component and former during cooling of the component being accommodated by the boron nitride coating on the former. The thickness of the coating can be determined by trials to achieve a controlled diffusion of carbon into the surface of the pressed component, and the dimensions of the former chosen to accommodate that thickness of coating.