Questions & Answers about Det som ødelægger farven, er laget af gammel lak.
Why do we use det som instead of hvad for "what" here?
In Danish, you cannot use hvad as the subject of a statement like "what is destroying the color". Instead, you use the pseudo-cleft structure det som (literally "that which"). The entire clause Det som ødelægger farven acts as the subject of the main verb er.
Can I omit som and just say Det ødelægger farven, er...?
No, som is strictly required here. In Danish relative clauses, you can only drop som if it acts as the object of the clause. Since som is the subject performing the action of the verb ødelægger, it cannot be omitted.
Why is there a comma right before the main verb er?
This follows the traditional Danish comma rules. The comma separates the entire subordinate clause Det som ødelægger farven from the main clause. Even though it feels like you are separating a subject from its verb, Danish requires a comma here to mark the clause boundary.
Why is the adjective gammel not inflected as gamle or gammelt here?
The noun lak is common gender (en lak) and is used here in the indefinite singular. Therefore, the adjective takes its basic, uninflected form gammel. If we were saying "the old varnish", it would require the definite inflection den gamle lak.