A type of chromatography that employs a thin layer on a flat glass support (often a glass plate with a silica gel layer). First, the substance being tested is applied to one end of the plate. Then, one end of the plate is placed in a solvent (known as the "mobile phase") and over time that solvent rises up the thin layer by capillary action. This process carries the substances being tested with it. As each different substance is drawn up at a different rate, separation occurs and analysis is possible.