Plasma emission spectra for different configurations and with the Swan bands. The basic configuration is a support made of aluminium that holds the pencil lead and a surrounding which is air. Only one parameter is changed in each experiment: the material of the support becomes wood or the gas inserted in the microwave oven which can be nitrogen or argon. As a reference, the spectrum without plasma and with the microwave oven on is also given. The Swan band are situated respectively at wavelength 437 nm, 470 nm, 505 nm, 550 nm, 600 nm and 660 nm.