This work was part of a COST 50 project aimed at ways to make revert IN 100 less prone to soundness defects and associated property degradations. It was based on carrots cast from 5 master distinct master melts, which were evaluated through metallography and Differential Thermal Analysis. Recycling was shown to affect grain size and morphology, carbide precipitation features, eutectic pool distribution and above all, microporosity level. The experimental evidence strongly suggests that, in revert master melts, carbides grow onto pre—existent nuclei made of TiN. This in turn reduces total heat of solidification, thus making the residual liquid substantially less fluid and consequently less capable of coxnpensating for solidification shrinkage in a dendrite structure which is more “tortuous”, because of its lower maturation rates. The effects of recycling can therefore be better accounted for in terms of bound nitrogen rather than of gas content as such.