Gum Tragacanth

Gum Tragacanth is an exudate of the Astragalus genus of plants in the Leguminosae family. Found in areas of Asia Minor, the gum is exuded through breaks or wounds in the bark of the shrub. Upon hardening, the Ribbon (the best commercial grade) and Flake grades are hand-picked, sorted, and further processed to their powder form.

Gum Tragacanth absorbs water to become a gel, which can be made into a paste. The significant fractions are known as tragacanthin, highly water-soluble as a mucilaginous colloid, and the chemically related bassorin, which is far less soluble but swells in water to form a gel.

An adhesive paste is formed when water is added to Gum Tragacanth, typically at a 2–4% concentration. This paste accounts for many of its uses in the food and pharmaceutical industries and art. While Gum Tragacanth solutions are slightly acidic with a pH of 5–6, they can be neutralized by adding small amounts of chalk or alkali. Tragacanth is relatively stable in a wide range of pH from 10 to extremely acid conditions of 2.5. Gum Tragacanth has good thickening, emulsification, and suspending properties.

Uses in Art

Gum Tragacanth makes watercolor megilp—a gel-like waterborne medium used by 19th- and early 20th-century watercolorists like John Singer Sargent. Gum Tragacanth is the traditional binder used in making artists’ pastels, as it does not adhere to itself the same way other gums (such as gum arabic) do when dry.* Gum Tragacanth is also used to make a paste used in floral sugarcraft to create lifelike flowers on wires used as decorations for cakes, which air-dries brittle and can take colorings. It enables users to get an excellent, delicate finish to their work. In the Middle East, particularly in Turkey, Gum Tragacanth is used in paper marbling to make the size upon which pigments float and form shapes, just as carrageenan is used in the West.

Directions

To prepare Gum Tragacanth solution for watercolor painting and artists’ pastels and crayons, add one teaspoon of Gum Tragacanth to 8 ounces of tap or distilled (preferred) water. Stir until completely dissolved. Store in a closed bottle in a refrigerator to avoid spoilage.

Further Reading

Please see the article on Historical Watercolor Mediums for more information about the use of Gum Tragacanth in watercolor painting.

* Mayer, Ralph (1991) The Artist’s Handbook of Materials and Techniques (5th ed.). Viking. p. 427. Quote: “chief use among artists’ materials is as a binder for pastel and chalk crayons.”