The phase diagram of the stable tetrahedron NaCl – KCl – PbCl2 – PbWO4 of the quaternary reciprocal system Na, K, Pb // Cl, WO4 was first studied using methods of differential thermal analysis. Its phase diagram was triangulated and stable triangulating internal sections of NaCl – PbWO4 – KCl.2PbCl2, NaCl – PbWO4–2KCl. PbCl2 and obtained tetrahedra NaCl – PbCl2 – PbWO4 – KCl.2PbCl2, NaCl – KCl – PbWP4, and NaCl – KCl – PbWP4. There are coordinates of three quadruple invariant points revealed.

There is a topology of the four-component reciprocal system Li, K, Pb ǁ Cl, WO4, its phase diagram was triangulated and stable tetrahedra revealed, the dominant chemical reactions of mutual exchange and complexation were determined. There are chemical synthesis of lead tungstate and lead oxide tungsten bronzes in ionic melts of the Li, K, Pb ǁ Cl, WO4 system carried out. A synthesis technology for lead tungstate in ionic melts is proposed based on the results.