The article presents the results of the physico-chemical tests concerning the properties of various slags formed after welding with low-hydrogen and rutile electrodes as well as flux-cored wires. The slags tested were analysed for their phase compositions using X-ray diffractometry (XRD) X-ray fluorescence (XRF). The behaviour of slags at temperatures elevated to 1400°C was examined using a high-temperature microscope. The analysis of the high-temperature tests enabled the determination of slag characteristic temperatures, i.e. softening and melting points. The results obtained demonstrated various properties of slags, with the lowest characteristic temperatures for low-hydrogen slags and the highest characteristic temperatures for flux-cored wire slags. In addition, on the basis of different characteristic temperatures slags were classified in relation to their solidification rates.