"Portrait of Pastor Swalmius" has been added to the list of authenticated Rembrandt works.

The discovery that a portrait thought to be by a pupil of Rembrandt was painted by the Dutch master himself has curators at the Royal Museum of Fine Arts here overjoyed, but for more than one reason. Not only has the painting’s estimated value increased overnight from €1 million ($1.4 million) to €20 million, but it also evens the score of one Rembrandt each with the Antwerp museum’s rival, the Royal Museum in Brussels.

Portrait of Pastor Swalmius was verified as a genuine Rembrandt after layers of discolored varnish were cleaned off and samples of its canvas were found to match the material used for two other masterpieces by the 17th-century artist. When the museum bought the painting in 1886, it was assured that it was a genuine Rembrandt, but eventually the varnish darkened considerably and experts were no longer sure. In 1969 the Rembrandt Research Project decided it was the work of a pupil; the museum was able to challenge this classification after a private donor provided money for the painting’s restoration. The Rembrandt Research Project has now added Pastor Swalmius to its list of works by the master.