They manufacture scientific apparatus according to the specifications of the scientist requiring the apparatus, or according to standard specifications. Other specifications are usually given in the form of a sketch. Sometimes glass instrument makers design the instruments themselves. The work of glass instrument makers involves the bending and forming of glass tubes, the blowing of reactor valves and the forming of gas waste-pipes, the partial machining of basic glass components and taps, as well as the mounting of such components by melting them together to form a complete apparatus. They make use of various techniques in the formation of glass components.