Caps are used for the purpose of closing or sealing a container. They are extremely common objects used on a daily basis, and even in the laboratory they perform an important function. Used by humans for thousands of years, caps have evolved to adapt to different types of containers and perform more complex tasks. This is why there are simple models and more sophisticated ones.
Caps are produced in different materials, depending on their container and the substance they are meant to seal. Like laboratory containers, they come into contact with acids and high temperatures. For this reason, they must be made of materials that do not deteriorate in contact with such substances. Common materials include rubber or neoprene, which are characterised by high chemical resistance, but also glass, silicone and polytetrafluoroethylene (PTFE).
Rubber plugs are generally produced in conical form and in about 16 different sizes, one for each standard container type. The size of the cap is essential in order not to allow leakage of the container, which could also be dangerous in some cases. As previously mentioned, rubber caps are commonly used during laboratory experiments due to the high chemical resistance of the material. They are also used for fermenting food or for applying high temperatures. Rubber models can be filled or perforated, i.e. with one or more holes in the centre of the instrument. This allows tubes to be inserted after the cap has already been applied and the container closed.
Glass stoppers are used with laboratory glassware, for example a flask or condenser. Compared to rubber or cork models, they have greater chemical and high temperature resistance. The outer edges that seal the container are ground to ensure a perfect fit. There are also screw-on glass models, unfrosted and with a straight edge.
There are various accessories used in the application of stoppers in the laboratory. For example, gaskets, which can be made of silicone or PTFE. These are used with perforated GL caps, usually made of polybutylene terephthalate (PBT). An additional accessory used with a cap is the corkscrew, made of polished brass. This is used to drill holes in rubber, neoprene or silicone caps to allow tubes to be inserted. It has a butterfly handle with a fixed grip. A corkscrew sharpener is used to sharpen it. This tool has a tempered steel blade and a rounded wooden handle.