The 'flask' was then trail-decorated, marvered and tooled before it was expanded on the blowpipe. The bottom was pushed in towards the rim with a pontil rod, and the vessel was cooled so that the blowpipe could be cracked off. The splayed foot was applied and flared out, and the vessel broken away from the pontil rod. The underside of the base is concave, but it retains no pontil mark; the latter is inside the bowl, within the original rim. Marvered glass may be described as a glass of one colour decorated with a trailed glass of another colour. The trails are flattened into the parent glass by rolling the object along a marble slab or 'marver' and being lent a pattern by combing. The technique was prevalent in Pharaonic Egypt, and from the Roman period onwards, its decoration was further enhanced by blowing. Fragments have been found over an extensive area at Islamic sites ranging from the Umayyad to the Mamluk period, with a concentration in Syria-Palestine and Egypt, both at Alexandria and Fustat. While it is difficult to exclude the possibility that the industry was directly continuing a Roman fashion, the vast majority of surviving pieces and fragments appear to date from the 12th and 13th centuries. However, marvered glass continued to be used for weights in Egypt up to the fourteenth century.