Thin-layer chromatography sheets are an integral part of the the TLC chromatography technique used to separate non-volatile mixtures into their component compounds or elements. TLC plates are usually made of glass, plastic, or aluminum foil coated with a thin layer of silica gel, aluminum oxide, or cellulose. This particular type of TLC plate is glass, 20 cm x 20 cm. In size, and has a fluorescent indicator for examination under exposure to UV light. High quality glass plates ensure that there is little to no UV cutoff factor to consider, and allows for close analysis free of distortion. The TLC technique is often used to monitor the ongoing progress of a reaction under study, ID and separate the various compounds present in a mixture, and measure the purity of any substances identified. The most common tests conducted using TLC are the analysis of ceramides and fatty acids, detecting pesticides and insecticide levels in food and water, and analyzing the dye composition of fibers in forensics.