Robert Wróblewski

Over the past six months, I have continued to experiment with indigo dyes. A major focus of this work has been the investigation of Maya Blue.

Maya Blue, an ancient pigment used by the Mayas and other Mesoamerican peoples in pre-Columbian times, can be seen as a precursor to a variety of inorganic-organic hybrid materials. The pigment is fascinating due to its remarkable stability, luminosity, and variety of colors, which has led to my continued interest. Yet the production of the pigment remains a mystery, as there are no historical records describing the Mayan production process.

Indigo is a vegetable dye obtained from Indigofera tinctoria or a similar plant species. Attapulgite is a fibrous magnesium aluminum silicate with high absorption capacity. Due to its needle-like structure and large surface area, it can bind and stabilize organic molecules. Pure attapulgite contains three types of water molecules: physically adsorbed water on the surface of the clay crystals, weakly bound water in the channels (zeolitic water,) and firmly bound water coordinated with the Mg2+ and Al3+ cations (structural water.) From a production point of view, there is general agreement that the preparation involves heating indigo (about 1 wt%) and attapulgite mixtures to more than 100 °C to promote the (more or less extensive) loss of water that is weakly bound to the clay channels. Normally indigo/attapulgite hybrids are made using this “dry” method, but the Maya may have used “wet” methods.

When experimenting with the dry method, these steps must be carried out carefully: Mixing attapulgite with indigo, heating the mixture, sedimentation, drying, and finally, grinding. It is best to mix attapulgite and indigo in a container with small porcelain balls. The container must be shaken for several minutes so that the indigo is well distributed with the attapulgite. Varying quantities of indigo (0.1g –0.4g) are added to a fixed quantity of attapulgite (10 g). Heating takes place at 110-180 °C for 2 hours in a heating cabinet. Below 110 °C the process is very slow, while at temperatures above 180 °C the indigo can be broken down or its chemical structure changed. The color of the mixture turns grey.

Sedimentation is carried out with cold water. First a little water is added to the mixture and then about 500ml of water is added to 10g of the indigo/attapulgite mixture. An Erlenmeyer flask is best suited for this. Depending on the mixing ratio, temperature, and time, some of the indigo may not remain combined with the attapulgite. A few minutes after the mixture has been stirred with water, the unbound indigo settles on the edge of the container and can be removed. The process is repeated until no more indigo pigment is visible at the edge.

The heavy particles must then be removed. After vigorous shaking, the heavy particles quickly settle to the bottom of the container. After pouring over the liquid mixture, a gray slime remains, which must also be removed. This gives the mixture a purer blue color. The consistency of the pigment also changes. When applying the color with a brush, the surface becomes less sticky and the color distribution on the paper becomes more even. Light particles that remain suspended for a long time are usually colorless. These can also be easily removed by sedimentation. The result is a more intense and less opaque color.

In addition to variations in the mixing ratios and different temperatures, I am planning further experiments in which attapulgite is mixed with indigo in different particle sizes. In addition, copal resin will be included as an additive in the production of Maya Blue, as it could further improve the stability and luminosity of the pigment.

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