Cuvette

A cuvette is a small tube of circular or square cross section, sealed at one end, made of plastic, glass, or fused quartz (for UV light) and designed to hold samples for spectroscopic experiments. The best cuvettes are as clear as possible, without impurities that might affect a spectroscopic reading. Like a test tube, a cuvette may be open to the atmosphere on top or have a cap to seal it shut. Parafilm can also be used to seal it.