L’éponge de potier lisse l’argile.

Because French shortens le or la to l’ before a vowel sound. This is called elision.

So:

• la éponge becomes l’éponge
• la argile becomes l’argile

Both éponge and argile are feminine singular nouns, but the article is shortened in front of the vowel.

Éponge is feminine: une éponge.

When you see l’, it could come from either le or la, so the apostrophe by itself does not tell you the gender. You usually learn the noun with its full article in another context, or you check a dictionary.

The same is true for argile, which is also feminine: une argile.

Here, de potier describes the type or use of the sponge. It is similar to saying potter’s sponge or sponge used by a potter.

In French, de + noun often works a bit like an adjective:

• roue de potier = potter’s wheel
• robe de mariée = wedding dress
• salle de bain = bathroom

So éponge de potier is best understood as a category or tool name, not just simple possession.

Because de potier and du potier do not mean the same thing.

• de potier = a sponge of the potter type, or a sponge associated with pottery/potters
• du potier = the sponge of the potter, meaning it belongs to a specific potter

So:

• l’éponge de potier = potter’s sponge / pottery sponge
• l’éponge du potier = the potter’s sponge, belonging to that potter

This is a very common distinction in French.

In this sentence, lisse is a verb.

It comes from the infinitive lisser, meaning to smooth. Here it is the third-person singular present form:

• il/elle lisse = he/she/it smooths

So:

• L’éponge de potier lisse l’argile. = The potter’s sponge smooths the clay.

It can also be an adjective in other contexts:

• une surface lisse = a smooth surface

But here, it is clearly a verb because it sits between the subject and the object.

The sentence structure shows it.

French is using normal subject + verb + object order here:

• L’éponge de potier = subject
• lisse = verb
• l’argile = direct object

If lisse were an adjective describing éponge, you would need a different structure, such as:

• L’éponge de potier est lisse. = The potter’s sponge is smooth.

So in your sentence, lisse must be the verb smooths.

The infinitive is lisser.

Present tense:

• je lisse
• tu lisses
• il/elle/on lisse
• nous lissons
• vous lissez
• ils/elles lissent

Your sentence uses il/elle/on lisse, because the subject l’éponge is singular.

French usually needs an article before a noun, even in places where English often leaves it out.

So French says:

• lisser l’argile

where English may simply say:

• smooth clay

Using l’ here is normal French. It can refer to:

• the clay being worked on in this context, or
• clay as the material in a general sense

If you said de l’argile, that would usually mean some clay, so the nuance would be a little different.

A rough English-friendly pronunciation is:

lay-PONZH duh po-TYAY lees lar-ZHEEL

A more precise IPA pronunciation is:

/le.pɔ̃ʒ də pɔ.tje lis laʁ.ʒil/

A few helpful points:

• éponge has a nasal vowel in the middle: pɔ̃
• potier ends like -tyay
• lisse sounds like leece
• argile has the French r and the g sounds like the s in measure