Black Liquid Underglaze is a deep, obsidian black that is dark and smooth at cone 05/06, fluxes into a soft glaze-like surface at cone 5/6, and maintains a deep black tone with a soft sheen at cone 10. Though the underglaze does become glaze-like, a clear gloss glaze can give Black a smooth finish with relatively good color, though it can some transparency.
Tableware producers must test all finished ware to establish dinnerware status, due to possible variations in firing temperature and contamination.