Tin Refining by Fire
Tin refining is an ancient process. It was first used in China, in around 2000 BCE and was perfected during the Roman period. The basic process is the same as that used today: tin ore, or “tin stone”, is heated in a powerful furnace – usually an open hearth or reverberatory one. The heat causes the tin stone to break down into its component parts, which consist of various metals, including tin and lead.
The tin is then separated from the other metals, usually through a process known as “washing”. In this process, water is added to the molten tin stone, turning it into a liquid which can be poured through a filter and strains out the tin. The other metals are denser and remain in the filter, while the lighter tin is able to pass through.
The purified tin is then subjected to a further refinement process known as “fire refining”. This involves heating the liquid tin with a combustible material in a sealed container, thus separating out impurities and removing any lead left over from the earlier washing process. This is done by keeping the temperature of the tin at around 500 to 550 degrees Celsius, so the impurities and lead can burn away without the tin itself melting.
The fire refining process is a very skillful, complex technique. It requires constant attention and strict temperatures, as the burning process can cause the tin to foam, discolor or even solidify if not monitored carefully. The skilled refiners must also be careful not to let oxygen into the refining chamber, as this can cause oxidation of the tin and create unwanted byproducts.
The process of fire refining is still used today in the production of tin, particularly in the making of tin ingots. Not only has it been perfected over many centuries, but it is also relatively cost-effective and easy to manage. It is also an important tool in the making of other metals and alloys, such as bronze and pewter. Alloys are created by adding other metals to the tin, such as lead and copper, in order to create a more durable metal product. It is due to fire refining that tin can take on any number of properties, from being very malleable to very strong.
In conclusion, tin refining by fire is an ancient technique which, though still used today, has a long and fascinating history. It is a complex process which requires skilled refiners to ensure the desired result is achieved. It is also used in the production of other metals and alloys, enabling tin to take on different properties which can make a vast array of products.
