Because of the cultural public benefit organisation status of the Kunsthal, your donation is free of the duty on gifts and death duty. It is thus used to the full to support the mission of the Kunsthal.

A one-off gift is partially tax deductible, with a threshold of 1% (minimal € 60) and a ceiling of 10% of the total income.
A periodic gift is 100% tax deductible, irrespective of its size, provided it is laid down in a donation agreement (a notarial deed is no longer required), is a fixed sum, and runs for a period of at least five years. 

The law on gift duty allows 125% tax deduction on donations until 1 January 2017 (under certain conditions). Your tax deductibility is thus larger than your donation.