Final answer:
The common element between firing clay in a hot kiln and polishing silver to remove tarnish is the chemical process known as reduction, where oxygen is removed from substances.
Step-by-step explanation:
The common element between firing a clay pot in a hot kiln and using polish to remove tarnish from silver is the chemical process of reduction. Reduction is the chemical reaction that is the opposite of oxidation, which refers to the removal of oxygen from a compound.
In a hot kiln, oxygen is withdrawn to create a reducing atmosphere, allowing for the desired color effects on pottery, as seen in ancient Greek black-on-orange pottery. Similarly, the tarnish on silver, which is an oxide of silver, is removed by reduction when using certain polishes, where a small amount of silver along with the tarnish is also taken away.