<p>Porosity remains a persistent defect in cast iron components, posing challenges in quality and reliability. Although experts often infer causes from a pore’s size, location, and surface features, these indicators are not sufficiently well known to identify the root mechanism consistently. This study introduces a novel experimental method to systematically correlate the type of gas and melt, the timing of pore formation, and its surface characteristics—an approach not typically addressed in conventional foundry analyses, but that could prove to be relevant to this practice. For this purpose, cast iron cylinders were melted under an inert atmosphere, where argon was carefully injected into the melt to form a stable bubble at constant pressure. Once fully solidified, the pore surfaces were examined via scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). Key observations include the formation of graphite films in both hyper- and hypoeutectic melt conditions, although the dendrite tips were uncovered by graphite. Under an inert atmosphere, this indicates that film growth occurs directly from the liquid metal when graphite is stable, which implies external gases are, at the very least, not the sole driver behind graphite film growth. These insights contribute to a more systematic understanding of pore surface characteristics and their relationship to solidification conditions. The methodology presented has the potential to be extended to active gases, different cast alloys, and broader solidification conditions.</p>