לא נוסיף גלזורה, אלא אם כן הקדר יבדוק את הדופן.

נוסיף is the future tense, first person plural form of the verb להוסיף (to add).

So:

• אוסיף = I will add
• נוסיף = we will add
• תוסיף = you/she will add
• יוסיף = he will add

In this sentence, לא נוסיף means we will not add.

Hebrew often uses the future tense for straightforward statements about what will or will not happen, just like English.

Hebrew usually negates the future tense with לא.

So:

• נוסיף = we will add
• לא נוסיף = we will not add

This is the normal way to say that something will not happen. There is nothing unusual here grammatically: לא simply comes before the verb.

אלא אם כן means unless.

Literally, it is something like except if:

• אלא = but/except
• אם = if
• כן = so / thus

Together, the whole phrase functions as a single expression meaning unless.

Examples:

• לא נצא אלא אם כן יפסיק הגשם = We will not go out unless the rain stops.
• לא נוסיף גלזורה, אלא אם כן הקדר יבדוק את הדופן = We will not add glaze unless the potter checks the wall/side.

In Hebrew, when talking about a future or hypothetical condition, it is very common to use the future tense in both parts of the sentence.

So:

• לא נוסיף... = we will not add...
• אלא אם כן הקדר יבדוק... = unless the potter checks...

In English, after unless, we often use a present form: unless the potter checks.
In Hebrew, the future יבדוק is completely natural in this context.

יבדוק is the third person masculine singular future form of לבדוק (to check / inspect):

• אבדוק = I will check
• תבדוק = you/she will check
• יבדוק = he will check
• נבדוק = we will check

הקדר means the potter. The prefix ה־ is the Hebrew definite article, equivalent to English the.

So:

• קדר = a potter / potter
• הקדר = the potter

The sentence is referring to a specific potter, or at least to the potter in the relevant situation, so the definite article is used.

את is the marker of a definite direct object in Hebrew.

In this sentence:

• יבדוק = will check
• את הדופן = the wall/side

Because הדופן is definite (the wall / the side), Hebrew adds את before it.

Compare:

• הקדר יבדוק דופן = the potter will check a wall/side
• הקדר יבדוק את הדופן = the potter will check the wall/side

Important: את usually does not have a direct English translation. It is a grammatical marker.

דופן literally means side or wall.

In a pottery context, it usually refers to the wall of the vessel, not a wall of a building. So here it likely means the side surface or wall of the ceramic piece.

That is why the sentence sounds technical or craft-related: the potter is checking the vessel’s wall before more glaze is added.

גלזורה is a real Hebrew word, especially in ceramics/pottery contexts, and it means glaze.

It is a somewhat specialized term, and learners may also encounter other words in related areas, depending on the field or register. But in pottery, גלזורה is perfectly understandable and appropriate.

Because it is a technical/artisanal term, it may feel less familiar than everyday vocabulary.

Hebrew allows both orders, just like English.

The sentence given is:

• לא נוסיף גלזורה, אלא אם כן הקדר יבדוק את הדופן.

But you could also say:

• אלא אם כן הקדר יבדוק את הדופן, לא נוסיף גלזורה.

Both are grammatical. The version in your sentence starts with the main statement we will not add glaze, and then adds the exception/condition unless the potter checks the wall.

This order is very natural and common.

A word-by-word breakdown is:

• לא = not
• נוסיף = we will add
• גלזורה = glaze
• אלא אם כן = unless
• הקדר = the potter
• יבדוק = will check
• את = marker of a definite direct object
• הדופן = the wall / the side

So the structure is:

Not + we will add + glaze + unless + the potter + will check + the wall/side

That is very close to standard Hebrew sentence structure, even though the most natural English translation will not always follow the words one by one.