Joseph Aspdin, a bricklayer and businessman from Leeds, obtains on October 21, 1824, British patent BP 5022, "An Improvement in the Mode of Producing an Artificial Stone", in which he coins the term "Portland cement" for the hardened material's resemblance to the limestone of the Isle of Portland, in Dorset. Aspdin's process — double calcination of limestone and clay, followed by pulverization — lays the foundation of the modern cement industry, gradually replacing traditional lime mortars and "Roman cement" (a single-fired material of uncontrolled composition that, despite the name, has nothing to do with the opus caementicium of antiquity). It should be noted, however, that the cement described in the 1824 patent does not exactly match today's Portland cement: it was his son William Aspdin who, around 1843-45, without patenting the change, discovered that calcining the mixture at a much higher temperature (forming clinker) produced a much stronger material, far closer to modern cement, effectively launching the "Portland cement" industry as it is known today.