Synthesis and Acid Resistance of Maya Blue Pigment*

Abstract

Maya blue is an organo‐clay artificial pigment composed of indigo and palygorskite. It was invented and frequently used in Mesoamerica in ancient times (eighth to 16th centuries). We analyse in this paper one of the characteristics of Maya blue that has attracted the attention of scientists since its rediscovery in 1931: its high stability against chemical aggression (acids, alkalis, solvents, etc.) and biodegradation, which has permitted the survival of many works of art for centuries in hostile environments, such as the tropical forest. We have reproduced the different methods proposed to produce a synthetic pigment with the characteristics of the ancient Maya blue. The stability of the pigments produced using either palygorskite or sepiolite has been analysed by performing acid attacks of different intensities. The results are analysed in terms of pigment decolouration and destruction of the clay lattice, revealed by X‐ray diffraction. Palygorskite pigments are much more resistant than sepiolite pigments. It is shown that indigo does not protect the clay lattice against acid aggression. We show that Maya blue is an extremely resistant pigment, but it can be destroyed using very intense acid treatment under reflux.

A combined synchrotron powder diffraction and vibrational study of the thermal treatment of palygorskite–indigo to produce Maya blue

“…Palygorskite (formerly attapulgite, name still in use for industrial applications) comes from Ticul, Yucatan, Mexico. This palygorskite has been studied in several works [8,13,24,34]. The particular sample employed in this study is mostly dioctahedral (y = 0.07) and exhibits a low level of Fe ll for Al substitution (x = 0.12), estimated from its NIR spectrum as in Ref.…”

“…He pointed out that (i) the channel structure of the clay is essential to obtain the acid stability (he failed to obtain stable pigments using plate clays), (ii) the necessity of heating to activate the interaction, and (iii) the effect of the particle size. Although Van Olphen and other authors state that MB (or analogous pigments) can also be made with indigo combined with sepiolite, the pigments made with sepiolite are much less resistant than those of made with palygorskite [8]. Van Olphen suggested a first structural mechanism of complex formation, by the positioning of the indigo molecules along the surface grooves of the clay.…”

“…Yet, a long lasting debate concerns the structural and chemical aspects of this organo-c1ay pig ment. The combination of an organic molecule (indigo) with a specific clay mineral (palygorskite) under moderate heating induce some transformations and interactions [5][6][7][8] in the indigo molecule that improve the color properties of the resulting complex with respect to bare indigo or the lll1heated mixture. In this formation process, the color changes from dark blue (indigo) to a more clear turquoise blue, characteristic of the Mesoarnerican blue artworks.…”

Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels

“…In the 60s, the composition of this pigment was elucidated and the durability of Maya Blue was imparted to the association of indigo heat-treated with fibrous clays (palygorskite and sepiolite) 7 . The exceptional chemical stability of Maya Blue is shown by the persistence of the blue colour in acid and oxidising conditions 8,9 . Maya Blue is now considered as one of the first ever artificial organic-inorganic hybrid 10 , and its exceptional stability is a source of inspiration in the design of new hybrid material 11,12,13,14,15 .…”

Nanocompósitos de poli(álcool vinílico) contendo materiais híbridos mimetizando o pigmento Azul Maya

“…Além de várias artigos reportando a interação de outros corantes na paligorsquita [10][11][12][13] , testes também foram realizados com o análogo da paligorsquita, a sepiolita, a qual demonstrou uma menor estabilidade química devido à sua pronunciada fragilidade estrutural [14] . Outras matrizes lamelares sintéticas como os hidróxidos duplos lamelares (HDL) e os hidroxissais lamelares (HSL) também foram intercaladas com corantes aniônicos azo e os materiais dispersos em polímeros, porém estudos de estabilidade química em longo prazo não foram reportados [15][16][17][18] .…”