- American Paintings in the Metropolitan Museum of Art, apparently written some time ago, notes: "Few of Cook's signed works are known today [sic], and many of his portraits may be classified as anonymous or erroneously ascribed to other contemporary artists. Although he lacked academic training, he became familiar with the conventional devices of high-style portraiture and translated them into his own stylized folk art idiom." While it is probably true that many more Cook portraits exist, either anonymous or wrongly attributed, research for this website suggests that a large number of his works are signed and clearly identifiable.
- Associated professionally with upstate New York and Canada; portraits said to have been in many private homes in Saratoga Springs
- During his early years in Kingston, Ontario, and Toronto, in addition to portraits, Cook (then also Cooke) painted portraits from prints, including those of Sir Walter Scott, Shakespearean actor John P. Kembel, and classical works such as Carracci's Magdalen. These may have provided him practice, perhaps some income, and samples to show potential clients.
- "Consistent" winner of art contests (1840s? 1847?) sponsored by The Cultivator (published in Albany by the NY State Agriculture Society) Exhibited: Toronto (1834, 1847, 1848); National Academy of Art & Design, New York City (1841, 1843, 1844, 1852, 1856, 1857, 1858, 1859; portraits appearing at NAD are so noted in portrait descriptions); Munson-Williams-Proctor Arts Institute, Utica, NY (1960, see Little Dandy)
- Critical assessment is mixed. Dr. Edward J. Barker referred to some of Cook's exhibited works in Toronto (1834) as "paltry daubs"; another observer called them "equal to the best in show." A modern critic observes that two of Cook's early Canadian military portraits showed nothing more than "ordinarily competent workmanship; though the skill shown is beyond what was customary at the time." In 1837 the Courier referred to him as "Toronto's respectable artist." The Rochester Democrat (4 March 1852) referred to his "transferring to canvas the features not only, but the living animated likeness, the speaking expression of the countenance..." From a 1967 catalog of the Middendorf Collection of American Painting and Historical prints: “[Cook’s] portraits lack the technical proficiency of characterization of such of his more accomplished contemporaries as Charles Loring Elliott and Thomas Hicks. His work often exhibits a naïve charm resembling that of the more sophisticated folk artists of the period.”
- His talents grew more refined than many contemporary "itinerants," with subjects emerging as distinct individuals; the growth of his talent may be seen clearly by comparing the early and more "primitive" Blaisdells and McVicars (both 1832) to Mrs. James Bradford (1847) or Lemuel Bush Pike (1890), his latest datable portrait.
- For materials, Cook used tongue-in-groove stretchers of poor quality wood, fine grain, pre-primed linen or canvas, and lean oil paints with little impasto; portraits covered with fine varnish layers. Cracking and some spotting are evident in all works due to varnish impurities and to application of paints over layers not yet dried.
- In letters Cook expresses concern about portrait longevity, noting that he did not use colors with arsenic as it fades and that he recommended bleach to lighten faded or yellowed oils. One critic (Dr. Edwards again) takes him to task for using "brick dust and lamp oil [?]." Cook apparently found himself occasionally redoing some of his faded portraits.
- In a letter as early as 1860, Cook implied that he was painting some (by no means all) portraits from photographs (see Sister of Colonel/General Graham (1860)), noting in one case that it was "more difficult, by far, than to paint from life." In at least one instance he apparently applied paint directly to a photo image; see Unidentified Woman (1865).
- The Rochester Daily Union (27 May 1854) reported "a new and elegant lamp for the locomotive 'David Upton'...." Placed on the engine, it was "in the shape of a pipe which regulates the draft of air, so the lamp burns steadily at all times." The lamp also boasted a device which supplied it with oil. "The portrait of Mr. Upton [for whom the engine was named] on the lamp, was painted by that talented artist, Nelson Cook, of this city...." Cook received $20 for his efforts.
- Apparently Cook painted at least one landscape, which he referred to as the Salvator (letter to Ransom, 31 Oct 1877, written from Rome, NY); this may have been a wishful or whimsical reference to the 17th century Italian Baroque painter of wild and "sublime" landscapes, Salvator Rosa, who apparently had an impact on some of Cook's contemporaries. He wished that he could crate it and send it to London, where he may have thought the market better. The location of such a painting, if it exists today, is unknown.