potassium hydroxide solution in proportion to the ammonium in a quantity of between about 0 1 to 10 times the crystallization products which are obtained are then ammonium potassium paratungstate mixed crystals akpw of the type wherein x is between 0 and 10 and n is between 4 and 10 or mathematically 0 lt x lt 10 4 u2266 n u2266 10 preferably x is between 1 1 and 6 8 the coefficient x can be termed a 34 portion factor 34 reduction of these akpw crystals in pure hydrogen leads to the formation of tungsten blue oxide portion factor x corresponding to the selected relationship between ammonium and potassium determines the composition of the tungsten blue oxide the resulting tungsten blue oxide will have a phase mixture of the following composition range i corresponding to portion factor 0 u2266 x u2266 0 6 85 to 95 crystalline portions 50 to 80 hexagonal ammonium potassium tungsten bronze of the composition m y wo 3 wherein m is at least one of nh 4 and k and y u2266 0 22 5 to 15 x ray amorphous portions range ii corresponding to a portion factor 0 6 lt x lt 1 6 a mixture of hexagonal ammonium potassium tungsten bronze tungsten oxide and hexagonal potassium polytungstate small presence of x ray amorphous portions range iii.