i e during indiffusion of the reaction products formed by the crystallisation inhibitors as for example in the case of the oxygen donors of a boron suboxide and incorporation thereof into the crystal layer structures of the boron nitride fig6 shows a tem picture at an extreme enlargement of 250 000 fold of amorphous boron nitride abn 2 prepared according to example 2 many small spherical centres forming in the boron nitride material itself in which centres the dissolution of the hexagonal boron nitride structure i e of the crystal lattice layer structure is initiated in fig7 the microstructure of abn 2 obtained according to the process according to the invention using potassium permanganate as a crystallisation inhibitor according to example 2 is illustrated in an optical microscope picture shown in phase contrast in 500 fold enlargement fig6 and 7 in particular show the absence of any symmetric elements such as edges angles holo hedra which are after all typical of crystalline substances of boron nitride fig6 shows the microstructure type which may be ideal for example for use in tools and which proves that even at high enlargements none of the features typical for crystal nuclei as mentioned above are present fig8 1 8 2 8 3 8 4 and 8 5 show various mounting geometries for the starting materials for the synthesis of ultrahard amorphous boron nitride according to the process according to the invention for the reaction chamber of a high pressure insert according to fig5 in these figures the dotted regions show the disposition of crystallisation inhibitors optionally in conjunction with catalysts.