text: Smelting and melting of copper and its alloys such as leaded bronze was done in crucibles similar to those of the Roman period which have thinner walls and flat bases to sit within the furnaces. The technology for this type of smelting started to change at the end of the Medieval period with the introduction of new tempering material for the ceramic crucibles.  Some of these copper alloy crucibles were used in the making of bells. Bell foundry crucibles had to be larger at about 60 cm. These later medieval crucibles were a more mass-produced product.
  The cementation process, which was lost from the end of the Roman to the early Medieval period, continued in the same way with brass. Brass production increased during the medieval period due to a better understanding of the technology behind it. Furthermore, the process for carrying out cementation for brass did not change greatly until the 19th century. 
  However, during this period a vast and highly important technological innovation happened using the cementation process, the production of crucible steel. Steel production using iron and carbon works similarly to brass, with the iron metal being mixed with carbon to produce steel. The first examples of cementation steel are wootz steel from India, where the crucibles were filled with good quality low-carbon wrought iron and carbon in the form of organics such as leaves, wood, etc. However, no charcoal was used within the crucible. These early crucibles would only produce a small amount of steel as they would have to be broken once the process has finished.
  By the late Medieval period, steel production had moved from India to modern-day Uzbekistan where new materials were being used in the production of steel crucibles, for example, Mullite crucibles were introduced. These were sandy clay crucibles which had been formed around a fabric tube. These crucibles were used in the same way as other cementation vessels but with a hole in the top of the vessel to allow pressure to escape.