or crucible 6 which receives a mold 2 having an upper cavity of suitable configuration for receiving a preform 3 a heating unit 5 surrounds the crucible 6 in the space between the case 1 and the crucible 6 the preform 3 is made of a suitable reinforcement material selected from the group consisting of silicon carbide particles aluminum nitride particles silicon nitride particles boron carbide carbon fibers and ceramic fibers the mold 2 can be made of a porous material to absorb gas escaping from the preform 3 at metal infiltration during the pressure treatment suitable materials for the mold 2 include graphite or porous ceramics alternatively the mold 2 may also be made of steel or of gastight ceramics e g aluminum titanate in vicinity of the lid 7 the interior space of the case 1 is connected to a pressure source 10 for supply of a pressure fluid opposing the preform 3 and resting upon the rim of the mold 2 is a block of feeder material 4 of fusible metal which upon heating melts and infiltrates into the preform 3 suitable examples for infiltration metal include aluminum magnesium copper silicon iron and alloys thereof the method according to the present invention is carried out as follows after placing the preform 3 into the cavity of the mold 2 the case 1 is closed by the lid 7 the heating unit 5 is started and the interior space of the case 1 is pressurized via the pressure source 10 thus the block 4 of fusible metal melts and is pressed by the prevailing pressure inside the interior space onto the preform 3 to infiltrate or permeate into the preform 3 after.