A detailed and critical review of the literature pertaining to Maya Blue led to the conclusion that the presence of indigo as an integral component of the pigment has not, as yet, been established by acceptable scientific criteria. A Maya Blue was prepared from indigo and attapulgite which had all the observed properties of the authentic pigment. Although the experiments performed in the present study can hardly be called scientific proof of the composition of the prehistoric material, they strongly suggest that the colorant was indigo, at least in one type of Maya Blue.
The strong emphasis usually placed upon the identification of attapulgite as the base mineral of Maya Blue seems to be an exercise in the use of identification equipment. The question of whether attapulgite, a clay of variable composition and available from widely separated sources, is the base of Maya Blue is immaterial. It appears that any clay containing palygorskite, sepiolite, montmorillonite, or possibly other minerals free of plate-like crystal structures can be converted to a Maya Blue pigment with all the observed chemical and physical properties of the authentic material.
The present experimental work and some reported observations regarding variations in shade and color of Maya Blue specimens suggest there may be more than one pigment so designated and that a blue mont-morillonite is one of the alternatives to an indigo-colored clay for post-firing decoration of pottery and mural painting.
The technical studies which form the basis for some of the conclusions reached will be found in the appendix to this report.