Learn Russian: Переписчик использовал сделанное монахом перо. - The copyist used a quill made by the monk.

This is the core rule of Russian participial punctuation! Because the participial phrase (сделанное монахом) comes before the noun it modifies (перо), no commas are needed. If the phrase came after the noun, you would have to use commas to separate it: Переписчик использовал перо, сделанное монахом.

Why is the participle in the form сделанное instead of сделанный?

Participles act like adjectives and must agree in gender, case, and number with the noun they modify. Here, the phrase modifies перо, which is a neuter, singular noun. Since перо is the direct object of the verb использовал, it is in the accusative case. The neuter singular accusative form of this participle is сделанное.

Why is the word монахом in the instrumental case here?

Сделанное is a passive participle, meaning 'made'. When you use a passive verb or participle, the person who actually performs the action is put into the instrumental case. So, монахом translates to 'by the monk'.

How is the word переписчик formed?