One attempt to replicate ignis fatuus under laboratory conditions was in 1980 by British geologist Alan A. Mills of Leicester University. Though he did succeed in creating a cool glowing cloud by mixing crude phosphine and natural gas, the color of the light was green and it produced copious amounts of acrid smoke. This was contrary to most eyewitness accounts of ignis fatuus. As an alternative, Mills proposed in 2000 that ignis fatuus may instead be cold flames. These are luminescent pre-combustion halos that occur when various compounds are heated to just below ignition point. Cold flames are indeed typically bluish in color and as their name suggests, they generate very little heat. Cold flames occur in a wide variety of compounds, including hydrocarbons (including methane), alcohols, aldehydes, oils, acids, and even waxes. However it is unknown if cold flames occur naturally, though a lot of compounds which exhibit cold flames are the natural byproducts of organic decay.