Lọ thủy tinh rất sạch.

Here lọ is a noun, meaning jar, bottle, or container, depending on context.

In this sentence, lọ thủy tinh means glass jar or glass bottle.

Although Vietnamese has classifiers, lọ itself is not just a classifier here. It is the actual thing being talked about. If you wanted, you could also say cái lọ thủy tinh, where cái is the classifier and lọ is the noun.

So:

• lọ = jar / bottle
• cái lọ = the jar / a jar

Both can occur in natural Vietnamese, depending on style and context.

In Vietnamese, words that describe the type or material of a noun often come after the noun.

So:

• lọ thủy tinh = jar made of glass
• literally, something like jar glass

This is normal Vietnamese word order. English usually puts this before the noun, as in glass jar, but Vietnamese often places it after.

Similar patterns:

• bàn gỗ = wooden table
• nhà gạch = brick house

So lọ thủy tinh is a very natural noun phrase.

It functions like a modifier, but it is originally a noun meaning glass.

In Vietnamese, nouns often modify other nouns directly, without needing a special adjective form. So thủy tinh in lọ thủy tinh means the jar is made of glass.

You do not need a word equivalent to English made of here.

So:

• lọ thủy tinh = glass jar
• not necessarily “jar that is crystal-clear,” but specifically “jar made of glass”

Because rất means very, and in Vietnamese it normally comes before the adjective or stative verb it modifies.

So:

• sạch = clean
• rất sạch = very clean

This is similar to English in meaning, though Vietnamese word order is simply:

• rất + adjective

Examples:

• rất đẹp = very beautiful
• rất lớn = very big
• rất tốt = very good

Because sạch is the predicate describing the subject.

Vietnamese often uses the pattern:

• subject + adjective/stative verb

So:

• Lọ thủy tinh rất sạch.
• literally: The glass jar very clean.

Vietnamese does not need a verb like is in this kind of sentence.

Compare:

• English: The glass jar is very clean.
• Vietnamese: Lọ thủy tinh rất sạch.

This is one of the most important differences from English.

In Vietnamese, when you describe something with an adjective, you usually do not need a copula like English is / am / are.

So:

• Anh ấy cao. = He is tall.
• Căn phòng sạch. = The room is clean.
• Lọ thủy tinh rất sạch. = The glass jar is very clean.

Vietnamese adjectives can act like predicates by themselves.

A word like là is generally not used before adjectives in this kind of sentence. Saying Lọ thủy tinh là rất sạch would be unnatural.

Yes, absolutely.

Cái lọ thủy tinh rất sạch is a very natural sentence. The difference is that cái is a classifier, and adding it can make the noun phrase sound more complete or more natural in many contexts.

Compare:

• Lọ thủy tinh rất sạch.
• Cái lọ thủy tinh rất sạch.

Both are understandable and natural, but the version with cái may sound slightly more conversational or more explicitly like the/a glass jar.

Whether the classifier appears depends on context, style, and how specific the speaker wants to be.

It can mean either, depending on context.

Vietnamese nouns often cover a wider range than a single English word. Lọ can refer to a bottle-like or jar-like container, especially one used to hold things.

So the best English translation depends on the situation:

• if it is wide and jar-shaped: glass jar
• if it is bottle-shaped: glass bottle

Without context, glass jar is often a safe guess, but both are possible.

In Vietnamese, many words that English treats as adjectives behave somewhat like stative verbs. Sạch is a good example.

That means it can describe a state directly without needing to be:

• Nhà sạch. = The house is clean.
• Tay tôi sạch rồi. = My hands are clean now.

So learners often call sạch an adjective, which is fine for basic learning, but grammatically it behaves more flexibly than English adjectives do.

No. Rất is common, but there are other possibilities.

For example:

• sạch = clean
• rất sạch = very clean
• sạch lắm = very clean / so clean
• khá sạch = fairly clean
• cực kỳ sạch = extremely clean

So rất is one common intensifier, but not the only one.

Vietnamese usually does not mark definiteness as clearly as English does.

So Lọ thủy tinh rất sạch could mean:

• The glass jar is very clean
• A glass jar is very clean

In real conversation, context tells you which meaning is intended.

If the speaker wants to be more specific, they can add other words, such as demonstratives:

• Lọ thủy tinh này rất sạch. = This glass jar is very clean.
• Lọ thủy tinh đó rất sạch. = That glass jar is very clean.

Normally no, because lọ thủy tinh is understood as a single noun phrase meaning glass jar/bottle, not glass by itself.

If you wanted to say The glass is very clean in the sense of the material or a drinking glass, you would usually use a different noun, depending on what you mean:

• Cái ly rất sạch. = The drinking glass is very clean.
• Kính rất sạch. = The glass surface is very clean.

So in your sentence, the most natural reading is specifically about a jar/bottle made of glass.