Oersted conducted an experiment in which he reacted aluminum chloride with a potassium amalgam alloy of potassium and mercury, producing a sample of aluminum which was of limited purity by reducing pressure and raising heat on the resulting aluminum amalgam. Although Oersted is the first scientist recorded as having produced aluminum, the element was theorized well before his time and experiments.
Oersted conducted his production experiments in 1825, but scientists and natural philosophers had discussed the material that came to be known as aluminum much earlier, dating back to 1787. The missing factor in their discussions was the extraction method which Oersted eventually pioneered and used to produce small amounts of the metal, confirming its existence.
Aluminum was massively expensive in the early 19th century, over $1,200 per kilogram, until new refining processes in the 1880s opened up the field of aluminum production and extraction. These processes relied on extracting aluminum from compounds like bauxite and aluminum oxide.
Aluminum is the most common metal found in the Earth's crust. It was initially difficult to acquire and purify because all naturally occurring aluminum exists in a bonded state with other alloys, elements and substances. This made it uniquely tricky to discover and begin to produce.