The invention relates to a glass having SiO2, Na2O and CaO as main components, which comprises two amorphous phases having different compositions, one of the two phases being in the form of inclusions dispersed in the volume of the other phase and comprising crystalline particles. An example contacting instrument includes a switch, a tone generator and a conductive mesh. The frame includes a rear swing frame pivotally connected to a front frame. The device can also include an interstitial electrode located between collector electrodes, an enhanced collector electrode with an integrally formed trailing end, and an enhanced emitter electrode with an enhanced length in order to increase emissivity.