Ultramarine – Not Just a Pigment of Traditional Folk Architecture Plasters

Ultramarine is a synthetic analogue of lazurite, so called lapis lazuli. It was applied first of all as a pigment of lime- and gypsum-based plasters of folk architecture. Ultramarine is still used as a pigment of building materials, and, it may act as a non-traditional pozzolanic material as well. The paper describes a laboratory synthesis procedure of blue ultramarine that is derived from historic formulas. Structural, and optical properties and phase composition of laboratory-produced samples were compared to the samples of folk houses plasters and to unused, contemporary and historic industrially-produced ultramarines. The means of powder X-ray diffraction, Raman spectroscopy, and polarizing optical microscopy were used. The properties of the laboratory-prepared samples were very close to the industrial ones. In the market, the commercially available ultramarines are blue, pink and purple. However, based on published data, it should be possible to produce green ultramarine by the modification of the production process. These colors were not reached during the laboratory experiments, even when the published formulas were precisely followed.