The commission's other findings suggested that the dust in the craquelure was too homogeneous to be of natural origin. The matter found in the craquelure appeared to come from India ink, which had accumulated even in areas that natural dirt or dust would never have reached. The paint had become so hard that alcohol, strong acids, and bases did not attack the surface, a clear indication that the surface had not been formed in a natural manner. The craquelure on the surface did not always match that in the ground layer, which would certainly have been the case with a natural craquelure. Thus, the test results obtained by the commission appeared to confirm that the works were forgeries created by Van Meegeren, but their authenticity continued to be debated by some of the experts until 1967 and 1977, when new investigative techniques were used to analyze the paintings (see below).