Hot ‘isostatic presses’ having all of the following, and specially designed components and accessories therefor: (a) A controlled thermal environment within the closed cavity and a chamber cavity with an inside diameter of 406 mm or more; and (b) Having any of the following: 1. A maximum working pressure exceeding 207 MPa; 2. A controlled thermal environment exceeding 1 773 K (1 500 °C); or 3. A facility for hydrocarbon impregnation and removal of resultant gaseous degradation products.