A furnace within a pressure vessel capable of withstanding 0-1 MPa and temperatures up to 600°C is described. The furnace allows the pyrolysis of injection moulded ceramics to take place at higher heating rates than is possible at atmospheric pressure without defects caused by bloating or cracking. The effectiveness of the method is described for a commercial injection-moulding composition pyrolysed in nitrogen. The various effects of gas pressure on the process are listed and the main beneficial effect is considered to be the increase in boiling point of the polymer-degradation product solution which forms the continuous phase. In the early stages of heat treatment, this allows more rapid mass transport both by diffusion and fluid flow.