Tin is obtained by reducing the ore cassiterite with coal in a reverberatory furnace. Limestone is added to produce a slag with the impurities, which can be separated.

$$ \mathrm{SnO}_2+2 \mathrm{C} \longrightarrow \mathrm{Sn}+2 \mathrm{CO} $$

Crude tin obtained from this process is contaminated with iron, copper, lead, and other metals. To purify it, the crude tin is remelted in an inclined furnace—a process known as liquation. During liquation, the easily fusible tin melts away, leaving the less fusible impurities behind.

Finally, the molten tin is refined using green poles of wood in contact with air. This step, known as poling, helps to oxidize any remaining metal impurities. These impurities form a scum on the surface, which can be removed.

This step-by-step process ensures the extraction and purification of tin from cassiterite.