Mana tahu seramik ini selamat di dalam tanur.

Literally, yes: mana often means which / where, and tahu means know. But mana tahu is a fixed expression in Malay.

Depending on context, it can mean things like:

• who knows
• maybe / perhaps
• you never know
• sometimes, with a different intonation, how would anyone know?

So learners should not translate it word-for-word as where know. In this sentence, it is best understood as an idiomatic expression, not a literal combination.

As written with a full stop, it looks like a statement.

That matters because mana tahu can be used in different ways:

• as a speculative opener: who knows / maybe
• as a rhetorical question: how would one know?

If you wanted a straightforward yes/no question such as Is this ceramic safe in a kiln?, Malay would more naturally use something like:

• Adakah seramik ini selamat di dalam tanur?
• Selamatkah seramik ini di dalam tanur?

So the punctuation and intonation are important here.

In Malay, demonstratives like ini (this) and itu (that) usually come after the noun.

So:

• seramik ini = this ceramic
• rumah ini = this house
• buku itu = that book

If you say ini seramik, that means something more like this is ceramic or this is a ceramic item, which is a different structure.

Malay often leaves out the verb to be in sentences like this. This is very normal.

So:

• seramik ini selamat = this ceramic is safe

There is no need to add a word for is in everyday Malay.

In more formal Malay, you may sometimes see adalah, but in ordinary sentences like this, leaving it out is the most natural choice.

Here, selamat means something like safe / suitable / not likely to be damaged or cause problems under those conditions.

When used with objects, selamat can work a bit like English expressions such as:

• oven-safe
• dishwasher-safe
• food-safe

So in this sentence, it does not only mean that the ceramic is not dangerous. It can also imply that it is suitable for being used in a kiln and will not fail under those conditions.

di dalam means in / inside.

• di marks location
• dalam means inside / in

So di dalam tanur means inside the kiln.

In many contexts, dalam tanur would also be natural. The version with di dalam is just a bit more explicit about physical location.

So:

• dalam tanur = in the kiln
• di dalam tanur = inside the kiln

Both can work, depending on style and emphasis.

This is a very important spelling point in Malay.

When di is a preposition meaning at / in / on, it is written separately:

• di rumah
• di sekolah
• di dalam tanur

But when di- is a passive prefix attached to a verb, it is written together:

• dibuat = made
• dipakai = worn/used
• dimasukkan = inserted/put in

So in your sentence, di dalam is correct because it is a location phrase, not a passive verb.

tanur usually means a kiln, furnace, or sometimes an industrial-style oven, depending on context.

For ceramics, tanur is a very suitable word because ceramics are often fired in a kiln.

If you mean a normal kitchen oven, Malay more often uses ketuhar.

So:

• tanur = kiln / furnace
• ketuhar = oven

Malay nouns usually do not change form for singular and plural the way English nouns do. So seramik itself does not tell you whether it is one item or more than one. Context does that.

In this sentence, seramik ini would usually be understood from the situation as this ceramic item / this ceramic piece / this ceramic object.

If you want to be more specific, Malay often adds a noun:

• pinggan seramik ini = this ceramic plate
• mangkuk seramik ini = this ceramic bowl
• barangan seramik ini = this ceramic item / these ceramic goods

Yes, it is understandable, but how natural it sounds depends on the exact meaning you want.

If you want a short, general statement, it works.

If you want to be more explicit, Malay might also say things like:

• Seramik ini selamat digunakan di dalam tanur.
• Seramik ini boleh dimasukkan ke dalam tanur.

Those versions make the intended meaning clearer, especially in instructions, product descriptions, or technical contexts.