 Only microscopic quantities of plutonium were available until the X-10 Graphite Reactor at the Clinton Engineer Works came online on 4 November 1943, but there were already some worrying signs.When plutonium fluoride was produced at the Metallurgical Laboratory, it was sometimes light colored, and sometimes dark, although the chemical process was the same.When they managed to reduce it to plutonium metal in November 1943, the density was measured at 15 g/cm3, and a measurement using X-ray scattering techniques pointed to a density of 13 g/cm3.