Cuvettes are a small plastic or glass tubes of circular or square cross section, usually sealed at one end. They are used to hold samples for spectroscopic analysis. Cuvettes may be open to the atmosphere at the top or have an additional cap to seal them shut.
In schools, disposable cuvettes are more common than the more expensive glass types. They are available in different material forms which match the range of spectra being studied.
Some cuvettes will be transparent only on opposite sides, so that they pass a single beam of light through the sample. Often the unclear sides have ridges or are rough to allow easy handling and to help place the cuvette in the correct position.
If your spectrometer uses glass cuvettes which are intended to be reused, when cleaning, ensure you do not use abrasive cloths or agents that may affect the opacity of the surfaces. This is a good reason for using disposable cuvettes which are commonly stocked by the main suppliers and fairly inexpensive.
Below are common types of cuvettes, the materials they are made from and their usable wavelength.