Inert granular material such as sand or gravel which is mixed with cement to make concrete or mortar, or with a binder to make some other solid compound. Sand is the most common aggregate. An aggregate might be added to a mixture to add strength, hardness, softness, color, texture, or economy. For instance, to make plaster easier to carve, one can add an aggregate of vermiculite or perlite (both available at gardening stores.)Related resource: Chalkboard has a section about manipulating a painting's surface with aggregates, modeling, impasto, and glazes. Chalkboard is produced by Ralph Larmann, a member of the art faculty at the University of Evansville, IN. Also see adobe, clay, filler, and manipulate.