Rudolf Oldenbourg. Thomas de Keysers Tätigkeit als Maler. Leipzig, 1911, p. 83, no. 93, as by Thomas de Keyser, crediting Hofstede de Groot with the attribution; calls it a half-length portrait of a man, supposedly the Earl of Northumberland; as in the collection of Mrs. Trollope.
Pieter J. J. van Thiel. Letter to Walter Liedtke. January 29, 1981, is "quite convinced" that this picture is by Werner van den Valckert.
J. Bruyn. Letter to Walter Liedtke. November 9, 1983, confirms his attribution to Pickenoy and calls the picture one of that artist's earliest known works.
J. Bruyn. Letter to Walter Liedtke. October 14, 1983, after seeing the painting reproduced in Ref. Thiel 1983, tentatively suggests that it is an early work by Pickenoy rather than a work by Van den Valckert.
P. J. J. van Thiel. "Werner Jacobsz. van den Valckert." Oud Holland 97, no. 3 (1983), pp. 165–66, 180, 195, no. 14, fig. 43, attributes it to Van den Valckert.
R. E. O. Ekkart in Dawn of the Golden Age: Northern Netherlandish Art, 1580–1620. Exh. cat., Rijksmuseum. Amsterdam, 1993, p. 596 n. 5, under no. 268, calls it an early work by Pickenoy, dismissing Van Thiel's [see Ref. 1983] attribution to Van den Valckert.
Walter Liedtke. Dutch Paintings in The Metropolitan Museum of Art. New York, 2007, vol. 1, pp. 528–30, no. 136, colorpl. 136.
Esmée Quodbach. "The Age of Rembrandt: Dutch Paintings in The Metropolitan Museum of Art." Metropolitan Museum of Art Bulletin 65 (Summer 2007), p. 61.