Plasma emission spectra for different configurations and with the N₂ First Positive System emission. 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 N₂ FPS are situated respectively at wavelength 632 nm, 639 nm, 647 nm, 654 nm, 662 nm, 670 nm, 679 nm, 687 nm, 716 nm.