famous patent for a method of making a cement he called "Portland cement". This was done by adding various materials together to make an artificial version of natural cement. The name "Portland cement" is also recorded in a directory published in 1823 being associated with William Lockwood, Dave Stewart, and possibly others. There then followed a number of independently discovered or copied versions of this "Portland cement" (also referred to as proto-Portland cement). Proto-Portland cement had a different chemical makeup from other natural cements being produced at the same time: It was burnt at a higher temperature than other Natural cements and thus crosses the barrier between traditional vertical kiln fired natural cement and the later horizontal kiln fired artificial cements. This cement is not, however, the same as the modern ordinary Portland cement, which can be defined as artificial cement. James Frost is reported to have erected a manufactory for making of an artificial cement in 1826. In 1843, Aspdin's son William improved their cement, which was initially called "Patent Portland cement," although he had no patent. In 1848, William Aspdin further improved his cement and in 1853, he moved to Germany where he was involved in cement making. William Aspdin made what could be called meso-Portland cement (a mix of Portland cement and hydraulic lime). Development in the 1860s of rotating horizontal kiln technology brought dramatic changes in properties, arguably resulting in modern cement. Certainly it is difficult to define whether an old render was a natural cement (single source marl) or an artificial one, but there is no doubt as whether the cement was fired in a vertical or horizontal kiln. The names natural cement or Roman cement then defines a cement coming from a single source rock. Early or proto-Portland cement could be used for early cement that comes from a number of sourced and mixed materials. There is no widely used terminology for these 19th-century cements. There had been, in order to rediscover this technology, two projects carried out by the European Union ROCEM and subsequently ROCARE (an ongoing project). Both these only deal with natural cement - referred to as Roman cement without reference to the early artificial cements. References Notes Bibliography Thurston A P, Parker's "Roman" Cement, Transactions of the Newcomen Society 1939 P193-206 (Newcomen Society) Major A J Francis, The Cement Industry 1796-1914 A History, 1977, Davis & Charles (Publishers) Ltd, Devon