Grey

Grey (often spelled gray in the U.S., see spelling differences) describes the colours ranging from black to white. These, including white and black, are known as achromatic colours or neutral colours.

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Tube

A tube is a soft squeezable container which can be used for thick liquids such as glue and toothpaste. Basically, a tube is a cylindrical, hollow piece with a round or oval profile, made of plastic, paperboard, or aluminum. Both ends of this tube are treated differently during the manufacturing process and filling. In general, on one end of the tube body there is a round orifice, which can be closed by different caps and closures. The orifice can be shaped in many different ways. Plastic nozzles in various styles and lengths are just one good example.

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Ceramic

A ceramic is an inorganic, non-metallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous (e.g., a glass). Because most common ceramics are crystalline, the definition of ceramic is often restricted to inorganic crystalline materials, as opposed to the non-crystalline glasses.

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Metal

https://de.wikipedia.org/wiki/Metalle

In 3D printing, ABS or PLA is usually used as the base material, to which a mixture of metal powder (copper, stainless steel, iron, bronze or brass) has been added. The squeezed out objects look and feel like metal.