Learn Italian: Le bilance di vetro sono lisce e la ragazza è snella. - The glass scales are smooth and the girl is slender.

This follows the spelling rule for feminine words ending in unstressed -cia or -gia. If the ending is preceded by a consonant, like the n in bilancia, the i is dropped in the plural, making it bilance. If it were preceded by a vowel, like in camicia, it would keep the i and become camicie.

Does the adjective lisce follow the same spelling rule?

Yes! The singular feminine adjective is liscia (smooth). Because the word ends in -scia, it follows a similar rule: the i is always dropped in the plural, changing the ending to -sce. Therefore, liscia becomes lisce.

Why do we say bilance di vetro instead of using a specific adjective for "glass"?

In Italian, materials are usually expressed using the preposition di (of) followed by the noun for the material, rather than using an adjective. So "glass scales" translates conceptually to "scales of glass" (bilance di vetro).

Why is there no definite article before vetro?

When stating what something is made of using di plus a material, you do not use a definite article like il or lo. It is simply di vetro, not del vetro, because you are describing the material in a general, descriptive way rather than referring to a specific piece of glass.