The thermal oxidation resistance of compounds of types RCo, R3Ni and RCu, where R is a rare earth element, has been tested by an isochronal method. It is found that the ratioTp/Tm of the oxidation parameter to the melting point decreases from about 0.75 to 0.6 with increasing atomic number, indicating a relaxation of chemical binding, and displays ‘saw-tooth’ variability as we pass from a compound of one element to another. This variability may be due either to weaknesses from valency-induced changes with elements such as terbium, or to deep-seated changes between odd- and even-Z elements. In a further development of the work, contours forTp/Tm of 0.6 and 0.7 have been charted on synoptic diagrams characterized by a constant row of 4f/5d elements on one ordinate and a variable 3d element (V to aluminium) on the other. We note that the largest area of high ground is found for cobalt compounds, followed by nickel, then copper; and that with copper only elements from barium to gadolinium contribute, in contrast with cobalt and nickel (lanthanum to at least thulium). Evidently a strong transition metal contribution to bonding in cobalt compounds has weakened in the copper counterparts, and s-d resonance/attenuation across the composite divide from the 4f element into the copper d-shell is only possible for the lighter rare earths.