About 70 fragments of Roman glass found in Cologne were analyzed. From the 43 fragments of the so-called natural colored glass, seven clusters could be formed. The composition of one of the clusters also includes the composition of samples of a glass furnace found in Cologne. Some fragments are so large that they allow a chronological ordering. The colorless glass, some 25 samples, forms two groups: high manganese and low manganese. Though Pliny does not mention the addition of lime, analyses, as well as archaeological findings, show that in the region of Cologne, with its very fine quartz, sand lime has been added intentionally.