BUCHAREST, Romania — A Romanian museum official says some of the paint pigments recovered from an oven of a woman whose son is charged with stealing seven multimillion-dollar paintings in the Netherlands contain chemicals from colors used in the 19th and 20th century, but aren’t commonly used anymore.

Forensic scientists at Romania’s National History Museum examined ash from the stove of Olga Dogaru, whose son is the chief suspect in last year’s theft of paintings, which include a Matisse, a Picasso and a Monet.

Authorities said Dogaru initially admitted burning the paintings to protect her son, but later denied it....