gloss with a metallic sheen, so characteristic of Greek pottery, emerged from the colloidal fraction of an illitic clay with very low calcium oxide content. This clay slip was rich in iron oxides and hydroxides, differentiating from that used for the body of the vase in terms of the calcium content, the exact mineral composition and the particle size. The fine clay suspension used for the paint was either produced by using several deflocculating additives to clay (potash, urea, dregs of wine, bone ashes, seaweed ashes etc.) or by collecting it in situ from illitic clay beds following rain periods. Recent studies have shown that some trace elements in the black glaze (i.e. Zn in particular) can be characteristic of the clay beds used in antiquity. In general, different teams of scholars suggest different approaches concerning the production of the clay slip used in antiquity. Firing Greek pottery, unlike today's pottery, was only fired once, using a very sophisticated process. The black color effect was achieved by means of changing the amount of oxygen present during firing. This was done in a process known as three-phase firing involving alternating oxidizing -reducing conditions. First, the kiln was heated to around 920–950 °C, with all vents open bringing oxygen into the firing chamber and turning both pot and slip a reddish-brown (oxidising conditions) due to the formation of hematite (Fe2O3) in both the paint and the clay body. Then the vent was closed and green wood introduced, creating carbon monoxide which turns the red hematite to black magnetite (Fe3O4); at this stage the temperature decreases due to incomplete combustion. In a final reoxidizing phase (at about 800–850 °C) the kiln was opened and oxygen reintroduced causing the unslipped reserved clay to go back to orange-red while the slipped area on the vase that had been sintered/vitrified in the previous phase, could no longer be oxidized and remained black. While the description of a single firing with three stages may seem economical and efficient, some scholars claim that it is equally possible that each of these stages was confined to separate firings in which the pottery is subjected to multiple firings, of different atmosphere. In any case, the faithful reproduction of the process involving extensive experimental work that led to the creation of a modern production unit in Athens since 2000, has shown that the ancient vases may have been subjected to multiple