is taken from the heart of the burl while plateaux is taken from the outer part of the burl. While both types of blocks can produce pipes of the highest quality, most artisan pipemakers prefer to use plateaux because of their superior graining. Clay Ceramic pipes, made of moulded and then fired clay, were used almost universally by Europeans between the introduction of tobacco in the 16th century, and the introduction of cheap cigarettes at the end of the nineteenth. The material is not very strong and the early varieties had long thin stems, so they frequently broke, but were cheap to replace. It has been claimed that this fragility was somewhat intentional as it was utilized by Colonial American tavern keepers, for example, in renting the clay pipes to patrons. When the patron was done smoking the pipe and returned it to the keeper, the end of the stem was simply broken off so as to be ready for the next patron. However, there is no documentary evidence for this practice; it is known that communal pipes used in taverns were cleansed by being heated in an oven on special iron racks. In England clay pipes were sold in bundles of dozens or twenties, and were often free in taverns, where the tobacco was sold. Forming the pipe involved making them in moulds with the bore created by pushing an oiled wire inside the stem. The preferred material was pipeclay or "tobacco pipe clay", which fires to a white colour and is found in only certain locations. In North America, many clay pipes were historically made from more typical terracotta-coloured clays. According to one British writer in 1869, the French preferred old pipes and the English new, the middle class preferred long stems and the working class preferred short. Short stemmed pipes, sometimes called cuttys or nose warmers in England, were preferred by manual laborers as they could be gripped between the teeth, leaving both of the smoker's hands free. Later low-quality clay pipes were made by slip casting in a mould. Higher quality pipes are made in a labour-intensive hand shaping process. Traditionally, clay pipes are unglazed. Clays burn "hot" in comparison to other types of pipes, so they are often difficult for most pipe-smokers to use. Their proponents claim that, unlike other materials, a well-made clay pipe gives a "pure" smoke with no flavour addition from the