Assistant-director of the Print Room of the Amsterdam Rijksmuseum (1913-1920); specialist in early Dutch graphic art and painting; art seller. Beets was born in Batavia, Indonesia which is present-day Jakarta. He was the only child of Dirk Beets and Clara Johanna van de Poll, and the grandson of the Dutch writer and poet Nicolaas Beets (1814-1903). He was raised in Batavia, then the capital of the Netherlands Indies. At the age of eight, he was sent to his mother's family in The Netherlands, in Driebergen. Later, he moved to Utrecht, where he attended the Gymnasium, living in the house of grandfather Beets and his aunts Ada and Aleid. He subsequently studied Law at Utrecht University. In 1903, he married Gerardina Maria van Regteren Altena. After having finished his law study, in 1904, he decided to dedicate his life to art, and in that same year, he was admitted to the Amsterdam Print Room as a volunteer. In 1907 he obtained a regular position as an assistant, under the direction of Ernst Wilhelm Moes. By that time he already had began publishing a series of articles on the Antwerp painter Dirck Jacobsz Vellert in Onze Kunst. A number of contributions on his favorite painter, Lucas van Leyden, and other sixteenth-century Leiden artists soon appeared in various periodicals, including the Bulletin Nederlandse Oudheidkundige Bond and Oud Holland. He also did innovative research on drawings of Albrecht Dürer. In 1913 he wrote a monograph on Lucas van Leyden, published in French, Lucas de Leyde (Collections des Grands Artistes des Pays-Bas). In that same year, Beets obtained the position of assistant director. For the exhibition on early Dutch painting and sculpture, held in Utrecht in 1913, he wrote the catalog of drawings. He continued publishing on sixteenth-century artists in Oud Holland and foreign periodicals, even after he left the print room in 1920. He then set up his own art business, from 1946 onward in association with S. J. Fontein. He regularly traveled to Paris, London, and other major cities. In 1935, he wrote a contribution on Dutch painting in the fifteenth and early sixteenth centuries in Kunstgeschiedenis der Nederlanden, edited by H. E. Van Gelder. In 1940 a Dutch monograph on Lucas van Leyden appeared in the Palet series. He remained active in the art market for the rest of his life. Beets was a self-made art historian. From 1907 onward, the Leiden and Utrecht universities offered a regular curriculum in art history. By that time, Beets already had found his way to the Amsterdam Print Room. His 1913 essay on Lucas van Leyden is evidence of his critical scholarship. Using connoisseurship he described and analyzed the oeuvre of this artist, which was kept in numerous museums and collections all over the world. I. Q. van Regteren Altena did not hesitate to compare Beets with Max J. Friedländer, though he admitted that Beets' innovative research occasionally had a speculative character, and that his contributions sometimes were questionable.
[complete bibliography:] Van Regteren Altena, I.Q. Lijst van geschriften in Jaarboek van de Maatschappij der Nederlandse Letterkunde te Leiden 1964-1965; Lucas de Leyde. Brussels: van Oest, 1913; De Nederlandse schilderkunst der XVe en van het begin der XVIe eeuw in Van Gelder, H. E. ed. Kunstgeschiedenis der Nederlanden. Utrecht: W. De Haan, 1936; Lucas van Leyden. Amsterdam: H. J. W. Becht, 1940.
Van Regteren Altena, I.Q. Nicolaas Beets Oud Holland 78 (1963): 85-86; and in Jaarboek van de Maatschappij der Nederlandse Letterkunde te Leiden 1964-1965: 40-48.