Lasittumista

Lasittumista is the Finnish term used to describe the process of glazing in ceramics. Derived from lasittaa, to glaze, it refers to forming a vitreous coating on ceramic surfaces through the application of a glaze frit and subsequent firing.

In practice, lasittumista involves preparing the ware, applying glaze by dipping, brushing, pouring, or spraying, letting the glaze dry, and firing in a kiln at temperatures appropriate for the glaze system. During firing, the glaze melts and bonds to the ceramic body, creating a glassy surface that adds color, sheen, water resistance, and durability. The composition typically includes silica, fluxes, and metal oxides for color.

Glazes are categorized by transparency and texture, including transparent, opaque, matte, and crystalline varieties. Tin-glazed and lead-containing glazes have historical significance in various ceramic traditions; contemporary practice often uses lead-free formulations for safety. The glazing process can also produce decorative effects through layering, engobes under the glaze, or salt and ash techniques.

Common defects include pinholes, crawling, crazing (network of cracks), and devitrification, all of which reflect issues with glaze chemistry, firing temperature, or application thickness. Proper fit between glaze and body, including a compatible coefficient of thermal expansion, is essential to avoid cracking.

In Finnish craft and education contexts, lasittumista is a standard term and skill taught in pottery studios and courses. See also glaze (ceramics), firing, and vitreous enamel.