I had this mandarin orange can. I filled the can with water. Four days later, there are quarter inch thick rust cakes on the inside of the can. Since I assume the can is aluminum, are these cakes aluminum oxide? If so, is it flammable and/or dangerous?Aluminum oxide is white and powdery in texture. It also takes a bit longer for aluminum to oxidize than iron, so I don\'t think you could have cakes of aluminum oxide in 4 days. If the cakes you are describing are reddish in color, then no, it is NOT aluminum oxide. It is good old fashioned ferric oxide- rust from iron.Mandarin orange cans are not generally made of aluminum. Most likely, it is steel with a tin coating on it. Aluminum oxide does not turn red, most likely this is iron oxide, otherwise known as rust metal oxides are not flamable. Heavy metals are hazardoues (lead, lead oxide...), but iron oxide is not, in fact, it\'s important to have iron in your diet, it is what makes your blood work! AstrobufOther related question