Thomsen decided to map out which kinds of phenomena co-occurred in deposits and which did not, as this would allow him to discern any trends that were exclusive to certain periods. In this way he discovered that stone tools were found in connection with amber, pottery, glass beads, whereas bronze was found with both iron and gold, but silver was only found in connection with iron. He also found that bronze weapons did not occur with iron artifacts - so that each period could be defined by its preferred cutting material. He also found that the types of grave goods varied between burial types: stone tools were found with uncremated corpses and stone-chamber tombs, bronze weapons and lurs in relation to stone-schist graves, and iron with chamber tombs in barrows. Thomsen was the first to use the terms Stone Age, Bronze Age and the Iron Age. When detractors asked rhetorically why there was no ”glass age,” Thomsen responded that glass beads were found in all three periods, but bowls of glass only in the Iron Age.