In September 2006, a new field survey of Lake Fazda in Wadi Natrun (Egypt) was undertaken to characterize the extant evaporitic deposits and reconstruct how this natural system was exploited in Egyptian and Roman times, especially in connection with glass production. It was found that the minerals currently precipitating in the lake are not immediately useful for the production of glass due to their high sulphate content. However, the large Roman glass-making factory of Beni Salama lies on the shore of the lake and was almost certainly exploiting its deposits for glass-making. Two solutions for this apparent contradiction are offered. First, the possibility that the lake has altered over time due to natural and human changes was investigated. The second solution is that some form of processing of the sulphate-rich deposits was carried out in antiquity to convert sulphate mineral phases to carbonates useful in glass production. Hints that this might be the case can be found in descriptions by Pliny, in his Natural history, and experimental work on using a ‘Leblanc’ type process to convert burkeite rich deposits into a usable glass-making flux were carried out, showing that this is a real possibility.