AMSTERDAM (AP).- Experts have reclassified a painting as a Rembrandt after years of attributing it to one of the Dutch master's students.

Ernst van de Wetering of the Rembrandt Research Project said Friday that X-ray analysis of "Bearded Old Man" has revealed outlines of a self-portrait of Rembrandt as a young man underneath.

He also cited stylistic analysis and circumstantial evidence in support of the conclusion that the painting — showing a man with unkempt white hair, lost in thought with just a hint of sadness — is by the Dutch master.

Van de Wetering dates the small (15 x 20 cm, 6 x 8 inch) but emotive painting to 1630, when Rembrandt van Rijn would have been 24 years old. Rembrandt's reputation as a portraitist was rapidly growing and he was preparing to leave Leiden for Amsterdam, which at that time was enjoying its golden age as a major naval power.

Van de Wetering said that the style and quality of the painting itself provide the strongest arguments for its authenticity, but the existence of the underlying portrait was important too.

"The light is typically Rembrandt in that it is so totally convincing: you perceive it as if you are looking at reality and not at a painting," he said.

"That was one of Rembrandt's great, great interests and also where he was so extraordinarily gifted, at portraying light so convincingly."

Classifying the painting as an authentic Rembrandt fills a hole in his historical record — a 1633 painting exists with an inscription that says it is a copy of "Bearded Old Man" by the Dutch master.

"Bearded Old Man" belongs to an unidentified private collector. It will go on display May-July of next year at the Rembrandt House Museum in Amsterdam, where the finding was announced Friday.

Van de Wetering collaborated with restorer Martin Bijl and technology professors Joris Dik of the Delft University of Technology and Koen Janssens of the University of Antwerp, among others in the reclassification.

Researchers used at least five different kinds of X-ray scans to analyze the chemical makeup of pigments in the painting and probe its hidden layers of paint. The scans were done at the Brookhaven National Laboratory in New York and ESRF in Grenoble, France.

Rembrandt produced hundreds of paintings, etchings and drawings, but new finds are extremely rare. However, four works formerly attributed to his students — a talented group in their own right — have been reclassified as by Rembrandt since 2008, often with the help of new technology.

Copyright 2011 The Associated Press.