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Blue minerals and gems have always been subjects of fascination to man. In particular lapislazuli is and was highly esteemed and also used as a precious stone and as a pigment. The host compound is the zeolite-type sodalite and the colour centres are S 2 2 and S 3 2 , whose amount ratio determines the specific hue, varying from violet blue to blue to green. But Se 2 2 can also be substituted into the sodalite cages in high percentages, giving the pigment a brilliant red colour. It is even possible to incorporate the rather voluminous radical species Te 2 and Te 2 2 into the sodalite matrix. Because the otherwise unstable colour centres are completely screened from the atmosphere and isolated from each other in the cages, they can be fully characterised by various spectroscopic techniques.

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It is shown by optical spectroscopy that indigo molecules, most likely incorporated into the channels of the palygorskite host structure, are the solely colour centres in the ancient Maya Blue pigment Ϫ in use during the Maya cultural period in Yucatan and Guatemala. This study also shows that the blue colour of solid indigo shifts toward turquoise and greenish hues when fastened to the host; it is suggested that the corresponding spectral modifications originate from the energy when single indigo molecules undergo hydrogen bonding with the hydroxy-groups in the channels (or in the open channels on the surface). Indeed artefacts from the Maya culture exhibit rather greenish than pure blue colours. Die Natur der Farbzentren im 'Maya-Blau' ؊ der Einbau organischer Farbstoffmoleküle in das Palygorskit-Gitter Inhaltsübersicht. Es läßt sich mit Hilfe der optischen Spektroskopie zeigen, daß Indigomoleküle Ϫ die vornehmlich in die Kanäle des Palygorskit-Wirtsgitters eingebaut sind Ϫ die einzigen Farbzentren des Maya-Blau sind Ϫ eines Pigments, das in der Maya-Kultur in Yucatan und Guatemala in Gebrauch war. Das Blau des festen Indigo ändert sich zu grün-blauen Farbtönen, wenn das Pigment-Molekül mit dem Palygorksit-Wirt 'reagiert'. Die entsprechenden spektralen Veränderungen sind sehr wahrscheinlich durch energetische Veränderungen verursacht, wenn isolierte Farbstoffmoleküle Wasserstoffbrücken-Bindungen mit den Hydroxylgruppen in den 97Similarly a tetrachloro-derivative of thioindigo forms hydrogen bonds with palygorskite, as evidenced by an again distinct colour change from red-violet to blueish-violet. Bulkier pigment molecules bearing hydroxy-groups, such as anthrachinon derivatives, seem to directly react with the host surface, but without producing very significant colour shifts.