Baking Pot Codex Restoration Project, Belize

Paint Layer Composition

Paints are typically composed of a combination of colorants, bulk additives, liquid carrier and binder. The analyzed paint layers contained colorant minerals in combination with significant quantities of various calcitic minerals; clay minerals and quartz (likely naturally occurring impurities) were also prevalent.

The colorants represent a diverse palette, sometimes mixed to produce different hues. Pseudomalachite [Cu₅(PO₄)₂(OH)₄] and malachite [Cu₂CO₃(OH)₂] formed the basis for all greens, and occurred with azurite [Cu₃(CO₃)₂(OH)₂] in the blue. Goethite [Fe³+O(OH)] was added to modify the olive green, and was the basis for the yellow and cream paints. Cinnabar [HgS] was the colorant for the most common red (salmon); the brick red was hematite [Fe₂O₃], and a mixture was present in the bright red, which occurred only as a small splotch on one fragment. The black was carbon-based, probably a plant charcoal.

All of the mineral constituents were generally finely crushed, with grain size of less than 15µm; this is considered microcrystalline, i.e., having a texture between 10-200µm [Bates and Jackson 1980:396]. The paint preparation of colors was coarser when used in monochromatic applications (on brown and red-flecked white grounds), than in polychromatic ones. A significant component of all paints, however, was "cryptocrystalline calcite" – areas in which crystals or grains are too small to be recognized as separate grains using ordinary magnification, i.e., less than 1µm [Bates and Jackson 1980:183]. Cryptocrystalline calcite is usually a good indication of a lime plaster technique, in which calcium carbonate raw materials have been processed with heat (calcining) and slaked (combined with water) [Shepard 1946; Hansen 2000].

Distinct calcium carbonate grains were also found, indicative of either impurities or additives. The presence in the white paint of aragonite, the least stable of the calcium carbonate minerals [Boynton 1980:29], suggests deliberate addition, either as a bulking material or colorant, possibly originating from ground shell.

The role of the binder in a paint mixture is to cohere the paint components, enhance working properties, and adhere the paint film to the substrate [Hansen et al. 1993: xv]. Binding media are often naturally occurring organic substances, such as exudates from bark or plants [Littmann 1960]; for example, such materials were identified in mural paintings from Bonampak [Magaloni et al. 1995a]. Analysis by FTIR detected no organic binder in the paint layers, but should be considered inconclusive; even if present, organic binding media may occur at levels below the technique’s detection limits. It is more likely that slaked lime served to bind the paint components and impart permanence, as Shepard [1946:273] concluded in her study of paints from various objects at Kaminaljuyu, including perishable objects; with such use, organic binders might be unnecessary [Fletcher 2002].

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