A tangka is a portable religious painting on cloth. In western Tibet, they are usually painted on coarse cotton weave that has been sized with a mixture of animal glue, chalk, and water. In paintings wider than eighteen inches, there is quite often a vertical seam joining two pieces of cloth because the local looms did not produce wider pieces. Pigments are either mineral or organic, producing rich colors compared to the garish modern chemical paints used in present-day tangka painting. The painting is then set in cloth borders, which are supplied with rods at the top and bottom so that the painting may be either hung or rolled up for storage or transport. The western Tibetan paintings in the Koelz collection quite often have only a plain dark-blue cloth at the top and at the bottom of the painting.
Not all the tangkas in the Koelz Collection were originally from western Tibet. Many of the other Tibetan paintings have borders, often of brocade, on all four sides. The borders on central Tibetan paintings have an iconography of their own that surrounds the subjects of the painting. In essence, the painting, along with its borders, encompasses the entire universe; the painting rises from its source as if on a lotus pedestal and is symbolically surrounded by the earth below, the sky above, and the Buddhist teachings on either side.