Learn Farsi: هر الماس سریع تراشیده شد.

In Farsi, the simple past passive is built by taking the past participle of the main verb and adding the simple past of شدن (to become). Here, تراشیده is the past participle of تراشیدن (to carve or shape) and شد is the "it" form of "became". So literally, the phrase translates to "became carved".

If "every diamond" refers to multiple diamonds, why is the verb شد singular?

Just like in English, the Farsi word هر (each/every) refers to individual items in a group. It must always be followed by a singular noun (الماس, not الماس‌ها) and it takes a singular verb (شد instead of the plural شدند).

Can I use the verb تراشیدن to say I "cut" a piece of paper or my finger?

No, تراشیدن specifically means to carve, scrape, shave, or shape a solid object. You will see it used for cutting gems, sharpening pencils, or shaving hair. To cut paper, food, or yourself, you would use a different verb like بریدن.

Where do adverbs like سریع (quickly) go in a passive sentence?

Adverbs that describe how an action is done usually go right before the verb phrase. In a passive sentence, the two-part passive verb (تراشیده شد) acts as a single block, so سریع is placed directly in front of it.