Fundamental to investigating the coexistence of superconductivity and magnetic ordering in GdSr2RuCu2Oy(Gd1212) is the fabrication of macroscopic crystallographically oriented samples. To achieve this, we need to identify the conditions in which Gd1212 incongruent melting reaction, producing solid GdSr2RuO6(Gd1210) in Cu-rich liquid, dominates over decomposition due to RuO2sublimation. Only in these conditions is it possible, indeed, to grow oriented samples by any melting and resolidifying technique. Moreover, the optimal mixture of Gd1212 and its melting products has to be identified to perform melt-textured or flux-flow growth. By means of thermogravimetric and differential thermal analysis (TG–DTA) we analyzed, up to 1200 °C in air, several mixtures of Gd1212 with Gd1210 or CuO, performing a scan of the entire CuO–Gd1212–Gd1210 coexistence line of the Gd–Sr–Ru–Cu–O phase diagram …