Keraamikko lasittaa maljakon sinisellä lasitteella.

Because maljakon is the object of the verb, and here it is a total object in the singular.

In this kind of normal affirmative sentence, a singular total object usually looks like the genitive, so maljakko becomes maljakon.

• maljakko = vase
• maljakon = the vase, as a completed/whole object

The idea is that the vase is being glazed as a whole item, not just partially or indefinitely.

Yes, but the meaning changes.

maljakkoa is the partitive form. It often suggests that the action is:

• ongoing,
• incomplete,
• repeated,
• or focused on the process rather than the finished result.

So:

• Keraamikko lasittaa maljakon. = The ceramicist glazes the vase / will glaze the vase as a complete object.
• Keraamikko lasittaa maljakkoa. = The ceramicist is glazing the vase / is working on the vase.

So maljakon fits best when the sentence presents the object as a whole.

Finnish does not normally use articles like English a/an and the.

So maljakko can mean:

• a vase
• the vase

Which one is meant depends on context.

The same is true for keraamikko:

• a ceramicist
• the ceramicist

English forces you to choose an article, but Finnish usually does not.

Both words are in the adessive case, marked by -lla / -llä.

Here the adessive expresses the means or instrument of the action, so it works like English with:

• sinisellä lasitteella = with blue glaze

So Finnish does not need a separate word meaning with here. The case ending itself carries that meaning.

The same case can also mean things like on, at, or by, but in this sentence it means by means of / with.

Because in Finnish, adjectives must agree with the nouns they describe.

So if lasitteella is in the adessive case, the adjective sininen must also be in the adessive:

• sininen lasite = blue glaze
• sinisellä lasitteella = with blue glaze

This agreement happens in both case and number.

Adjectives ending in -nen change their stem in most cases.

So:

• sininen = blue
• stem in oblique cases: sinise-
• adessive ending: -llä
• result: sinisellä

This is a very common pattern:

• punainen → punaisella
• toinen → toisella
• ihminen → ihmisellä

So sininen is not irregular in a strange way; it follows a common -nen pattern.

Because lasite belongs to a noun type where the stem changes in the oblique cases.

So the forms go like this:

• lasite = glaze
• oblique stem: lasittee-
• adessive ending: -lla
• result: lasitteella

This is the same pattern as words like:

• osoite → osoitteella
• tuote → tuotteella

So the extra tt and ee are part of the normal stem change for this word type.

This is because of vowel harmony.

Finnish case endings often come in two versions:

• -lla
• -llä

Words with back vowels like a, o, u usually take back-vowel endings such as -lla.
Words with front vowels like ä, ö, y, or words with only neutral vowels e, i, usually take front-vowel endings such as -llä.

So:

• sininen has only neutral vowels, so it takes -llä → sinisellä
• lasite contains a, so it takes -lla → lasitteella

Each word follows vowel harmony separately, even inside the same phrase.

Lasittaa means to glaze.

In this sentence, lasittaa is the 3rd person singular present tense:

• keraamikko lasittaa = the ceramicist glazes

But the dictionary form, the infinitive, is also lasittaa. So the infinitive and the 3rd person singular happen to look identical in writing.

This happens with many Finnish verbs ending in -taa / -tää:

• antaa = to give / gives
• unohtaa = to forget / forgets
• lasittaa = to glaze / glazes

You tell which one it is from the sentence structure.

Yes. They are directly related.

• lasite = glaze
• lasittaa = to apply glaze, to glaze

So the verb is basically built from the noun.

This kind of relationship is very common in Finnish vocabulary.

Keraamikko usually means a person who works with ceramics, such as:

• a ceramic artist,
• a ceramist,
• sometimes roughly a potter, depending on context.

So it is a profession/role word. In this sentence it is the subject:

• Keraamikko = the ceramicist
• lasittaa = glazes
• maljakon = the vase
• sinisellä lasitteella = with blue glaze

No, Finnish word order is fairly flexible, but this sentence uses a very neutral order:

• Keraamikko lasittaa maljakon sinisellä lasitteella.

That is a straightforward subject + verb + object + adverbial/instrument order.

You can move parts around for emphasis, for example:

• Sinisellä lasitteella keraamikko lasittaa maljakon.
• Maljakon keraamikko lasittaa sinisellä lasitteella.

These are possible, but they sound more marked and depend on context. For a basic statement, the original order is the most natural.

Because Finnish often uses cases instead of prepositions.

English says:

• with blue glaze

Finnish says:

• sinisellä lasitteella

The ending -lla / -llä already includes the idea of with here. So instead of adding a separate word, Finnish changes the form of the noun phrase.

That is one of the biggest differences between English and Finnish grammar.