What part of speech is polish in the sentence silver will tarnish if it not polished often?

In the sentence "Silver will tarnish if it is not polished often," the word polished is the past participle of the verb "polish".

Here's the breakdown:

* Verb: "polish" (to make something shiny by rubbing)

* Past participle: "polished" (used in this case as part of the past participle phrase "not polished")

The past participle acts as an adjective modifying the noun "silver" in the sentence.