Yugoslavian banknotes 1955 in ultraviolet

Does anyone know how Yugoslavian banknotes, series 1955, should look in ultraviolet? Should they be dark or bright?

If they are out of cotton paper it should not be fluorescent maybe some little spots here and there from foreign materials like microorganisms from the raw cotton.

I´m asking about this exact series because our client found out that these banknotes are different from all the others: they look bright, like clean office paper. Is it normal for this exact series, or they were somehow manipulated (washed, etc.)?