Sepiolite is a fibrous clay mineral and consists of 2:1 silicate blocks connected at the corners and separated by tunnels (channels on external surfaces) that extend in the direction of fiber length. The tunnels, 3.7 Å × 610.6 Å in cross-section, are responsible for the incorporation of organic and inorganic compounds. The present study aimed to examine the capacity of twelve different organic molecules, such as pyridine, indigo, methylene blue, and quaternary amines, to gain access to the tunnels of sepiolite using quantum chemistry techniques. The interaction energy computations performed at the B97-D/TZVP level showed that all of the considered organic molecules tend to access the tunnels of sepiolite if external water molecules are absent. This finding is in agreement with experimental studies that included pyridine, indigo, 2,2-bipyridyl, and methylene blue. Interestingly, 2,6-dimethyl pyridine preferred to remain in a tunnel rather than an external channel of the sepiolite.

Palygorskite-indigo and sepiolite-indigo adducts (2 wt.% indigo) were prepared by crushing the two compounds together in a mortar and heating the resulting mixtures at 150 and 120°C, respectively, for 20 h. The samples were tested chemically to ensure that they displayed the characteristic properties of Maya Blue. Textural analysis revealed that no apparent changes in microporosity occurred in sepiolite or palygorskite after thermal treatment at 120°C (sepiolite) and 150°C (palygorskite) for 20 h. Micropore measurements showed a loss of microporosity in both sepiolite and palygorskite after reaction with indigo. The TGA-DTG curves of the sepiolite-indigo and palygorskite-indigo adducts were similar to their pure clay mineral counterparts except for an additional weight loss at ∼360°C due to indigo.

The 29Si CP/MAS-NMR spectrum of the heated sepiolite-indigo adduct is very reminiscent of the spectrum of dehydrated sepiolite. Crushing indigo and sepiolite together initiates a complexation, clearly seen in the 13C CP/MAS-NMR spectrum, which can be driven to completion by heat application. In contrast to the broad peaks of the pure indigo 13C CP/MAS-NMR spectrum, the sepiolite-indigo adduct spectrum consists of a well-defined series of six narrow peaks in the 120.0–125.0 ppm range. In addition, the sepiolite-indigo spectrum has two narrow, shifted peaks corresponding to the carbonyl group and the C-7 (C-16) of indigo. A model is proposed in which indigo molecules are rigidly fixed to the clay mineral surface through hydrogen bonds with edge silanol groups, and these molecules act to block the nano-tunnel entrances.

The Shahnamah (RAS 239) copied for the Timurid prince, Muhammad Juki (1402–1445) in Herat, has long been considered one of the finest surviving, illustrated Timurid manuscripts. It was presented to the RAS in 1834 by Lieutenant Colonel Doyle (1787–1848), but attracted little scholarly attention until Barbara Brend published her monograph in 2010. The manuscript contains 31 exquisite miniature paintings, two of which (fol. 430v and fol. 531r) were added later during the Mughal period (1526–1761). This article will examine the sumptuous, jewel-like colours employed to depict scenes from the epic and the metals, pigments, and dyes from which they were derived. Precious metals and organic colours made from plants such as indigo and lac extracted from female insects are examined in detail: the methods of their production and extraction, the techniques used for their application, their commercial value, and the prestige they afforded their patrons all contribute to an understanding of what constituted the miniature painters' palette in the Timurid period.

Pigments similar to the famous Maya Blue were prepared by entrapment of indigo inside the channels of natural zeolites such as clinoptilolite and mordenite. The zeolites were mixed and ground with indigo and then heated at 150°C. Surplus (unbound) dye was removed by solvent extraction or by vacuum sublimation. As is the case when synthetic zeolites are used as matrices, the colouration of the resulting pigments could be modified by the previous cation exchange of the zeolite.

The use of nonallergic, nontoxic, and eco-friendly natural dyes has become a matter of significant importance due to increased environmental awareness on the need to avoid hazardous synthetic dyes. This study was to determine the staining properties of the dye extract of Lonchocarpus cyanescens on histomorphology of the testis. Freshly cut leaves of L. cyanescens obtained from Akpan Ifia Inan village in Ikono local government area of Akwa Ibom state (latitude 5° 10′ 12″ N; longitude 7° 48′ 0″ E) were put into a plastic jar and boiling water was poured to cover the leaves. It was covered and left for an hour. The liquid was strained and potassium hydroxide was added to the dye water mixture to reach a pH of 9. A whisk was used to mix air into the liquid, and the mixuture was then allowed to sit until the blue indigo had settled to the bottom of the container. The dye was diluted with 70% ethanol to a concentration of 0.1 g/mL and was used to stain sections of testes. Its potential for use as a counterstain was also investigated. The testes sections were stained in shades of blue. The dye overshadowed the colors of haematoxylin and eosin. Preliminary phytochemical screening of L. cyanescens revealed that it contains alkaloids, saponins, flavonoids, and tannins.

Woad (Isatis tinctoria L.) was the most important source of natural blue indigo, a pigment used mainly for dyestuff until the beginning of the 20th century, when the increased use of synthetic dyes by the industry lead to a decrease in the interest of natural dyes and to the abandonment of dye crops. The aim of this study was to characterize, according to morphological and agronomical traits, 11 woad accessions from different countries and to quantify the indigo precursor content by high-performance liquid chromatograph-diode array detection (HPLC-DAD). Qualitative traits revealed a low variability and a great variation was observed in quantitative traits. Principal component analysis (PCA) diagrams divided the accessions into four groups, primarily according to their geographic origin. The first three components of the PCA accounted for 76.8% of the total variation. Reciprocal interactions between indigo precursors and fresh leaf weight were compared through genetic diversity, with significant differences in isatan B (0.5–5.1 g/kg), indoxyl (0.3–2.0 g/kg) and residual indigo (0.3–0.5 g/kg). This information, together with genetic data, can be used to assist local farmers to re-introduce Isatis species in the European agricultural system, not only indicating the higher indigo yielding genotypes, but also the most suitable harvest time.

Maya Blue is a colour that is more than a pigment; it had roles in status, ritual and performance, being daubed onto pots and people before sacrifice. Here researchers use experimental and historical evidence to discover how it was made, including direct scientific analysis of Maya Blue on a pot thrown into the sacred well at Chichén Itzá. The results indicate that the formation of the colour was actually part of the ritual.