Sand-cast (Tufa) — Navajo Casting in Volcanic Stone
Sand-cast (Tufa) — Navajo Casting in Volcanic Stone
A southwestern American Indigenous casting tradition that uses carved volcanic tufa as a one-off mould
Tufa casting, often called sand casting in the Navajo and broader southwestern American Indigenous silversmithing tradition, is a casting technique in which molten silver is poured into a mould carved from tufa — a soft, porous volcanic ash deposit. The technique has been practised by Navajo silversmiths since approximately the late nineteenth century, when silverwork as a Navajo craft tradition first emerged following the introduction of metalworking technology and silver coin stock to the Diné people. Tufa casting produces a distinctive matte, slightly textured surface and supports one-off design work in ways that more elaborate casting techniques do not, with the result that the technique remains a hallmark of contemporary Navajo silverwork alongside other Diné traditions including stamp work, repoussé, and lapidary integration.
The material
Tufa is a sedimentary deposit of volcanic ash that has been compacted but not lithified into hard rock. It occurs in the volcanic regions of the American Southwest, particularly in northern New Mexico, where ancient volcanic activity produced ash deposits that have weathered into the soft, workable stone the silversmiths use. Tufa stone is light in weight, can be cut and shaped with simple hand tools — knives, files, gravers, dental tools — and crucially has a high enough silica content to withstand the temperatures of molten silver without disintegrating. The porosity allows gases generated during casting to escape through the stone, which is essential for sound castings without bubble defects.
Tufa for silversmithing is sourced principally from the volcanic regions of New Mexico, with traditional sources including locations near Acoma, Shiprock, and Albuquerque. Smiths typically reuse tufa stones across multiple castings, with each casting limited to one use of any specific carved mould before the stone is reshaped or discarded. The constraint that each mould produces only one casting is fundamental to the technique and gives tufa-cast pieces their unique-object character.
The technique
The smith begins by selecting a piece of tufa large enough to accommodate the design plus pouring channels and risers. The stone is split into two halves with flat mating surfaces — typically by sawing or controlled splitting along a planned plane. The design is then carved into one or both halves of the tufa, with attention to the depth and undercut of the design and to the arrangement of pouring channels (sprues) that will admit the molten metal and risers that will allow gases to escape and provide reservoirs of molten metal to feed shrinkage during cooling.
The two halves of the tufa are clamped together — traditionally by hand-binding with leather or wire — and the molten silver poured through the sprue. After cooling, the halves are separated, the casting removed, and the tufa typically reused for one further design before disposal or reshaping. The casting itself is then cleaned of sprues and casting flash, finished by filing and abrading, and integrated with stones, stamp work, or further fabrication as the design requires.
Aesthetic and design
Tufa-cast surfaces have a distinctive matte texture that arises from the granular structure of the tufa stone — the surface of a tufa cast carries the impression of the tufa's own micro-texture and reads as soft, organic, and warm in a way that polished sheet metal does not. This texture is a defining aesthetic of Navajo silverwork and is highlighted by selective polishing that lightens the high points while leaving the recesses dark, producing a pronounced visual contrast.
The design vocabulary of Navajo tufa casting is broad, ranging from the geometric and stamped patterns characteristic of nineteenth-century Diné silver to the more sculptural, organic forms developed by twentieth- and twenty-first-century smiths. Notable contemporary Navajo silversmiths working in tufa casting include Cody Sanderson, Kee Yazzie, and a generation of younger smiths who have extended the tradition into contemporary jewellery and into sculptural object work. Pieces are typically signed or hallmarked with the smith's mark and Navajo Nation hallmarks, and authentication relies on knowledge of the maker's marks and provenance to recognised dealers.
Stones and integration
Navajo tufa-cast jewellery commonly integrates turquoise, coral, jet, mother-of-pearl, and other stones characteristic of the southwestern silverwork tradition. The stones are typically set after the casting is complete, using bezel or shadowbox settings that integrate with the cast form. The combination of cast silver and set stones produces the characteristic Diné jewellery aesthetic that has been the defining vocabulary of Navajo silverwork for more than a century.
In the trade
For dealers handling estate or contemporary Native American work, tufa-cast pieces are recognisable by the matte casting texture and by the unique-object character of each piece. Authentication relies on maker's marks, provenance documentation, and consistency with known design vocabularies. The Indian Arts and Crafts Act of 1990 (United States federal law) imposes specific representation requirements for Native American-made jewellery, and dealers should observe those requirements in describing tufa-cast Diné silver.