Learn Italian: Vedo una bella scultura e un bel bronzo. - I see a beautiful sculpture and a beautiful bronze.

When bello comes before a masculine singular noun, it changes to match the definite article that the noun would take. Because we would say il bronzo, we use bel bronzo. We only use the full word bello before masculine nouns that take lo, such as words starting with a "z" or an "s" plus another consonant.

The word scultura starts with "s" plus a consonant. Why don't we use a special form of bello here?

Because scultura is feminine. The special phonetic rules for words starting with "s" plus a consonant only apply to masculine words. For feminine words starting with any consonant, you always simply use bella.

Can I place the adjectives after the nouns, like una scultura bella e un bronzo bello?

Yes, but placing bello before the noun is the most natural and common way to say this in Italian. Moving it after the noun adds a very strong emphasis to the beauty. Also, notice that if you put the adjective after the noun, you must use the full masculine form bello instead of the shortened bel (un bronzo bello).

I learned that bronzo means the material "bronze". Why is it countable here with un?