| http://www.w3.org/ns/prov#value | - In a particular embodiment of variant (a) of process (1) according to the invention, the azulmic acid is reacted with 0.2 to 80% strength phosphoric acid or phosphorous acid in the presence of naturally occurring hydrolytically degradable substances, such as, for example, celluloses, hemicelluloses, sugars, lignin, polymeric quinones, wood powder, vegetable material, polypeptides, such as gelatins
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