This is a very major exhibition devoted to the work of a very minor itinerant artist – John Church Dempsey (c.1802-1877).

Dempsey was active in England from the early 1820s through to his death in 1877, aged 74. He worked as a miniature portraitist, a silhouette artist and later as a photographer. He is an obscure artist, rather than totally unknown, and was one of hundreds of such itinerant artists who moved around Britain offering to take likenesses.

This exhibition stems from a folio of 52 watercolour illustrations made by Dempsey mainly in the 1820s, when the artist was in his early 20s, which John Docker presented to the Tasmanian Museum and Art Gallery in Hobart in 1956. For some reason, one of the drawings was separated from the rest and ended up at the Alexander Turnbull Library, National Library of New Zealand Te Puna Matauranga o Aotearoa in Wellington. The folio is being shown together for the first (and predictably the last) time. The exhibition has been the brainchild of David Hansen, who has researched it with passionate obsession for many years and who is also the author of a handsome 262-page book written to accompany the show. Those in the art world would remember Hansen best as the curator of the splendid John Glover exhibition that came to Canberra in 2004.

What is so important about Dempsey for him to be awarded such a major exhibition at the National Portrait Gallery in Canberra? This question is a bit difficult to answer as Dempsey is not a distinguished artist nor does he have any links to Australia. He does not appear to have been a trained artist and his treatment of the human anatomy is simply appalling; he also lacks basic knowledge of compositional structure and has no grasp of perspective. He appears to have been self-taught and mastered the skills of miniature portraiture and proceeded to replicate in his images of faces the most minute variations in textures, hairs, warts and skin blemishes. Dempsey's portraits are not so much warts and all images of people's faces, but rather images where the warts dominate the face.

The subject matter is not unusual for what is popularly described as British Regency art, a period that stretched from 1811 to 1837 and the accession of Queen Victoria. The Dempsey folio of watercolour drawings deals mainly with street people – the poor, the dispossessed, the war cripples, beggars and the disabled – eking out a living, the best they can, through sweeping paths on filthy streets for the gentry to pass unscathed by reality or selling matches, street food or daily supplies. Dempsey clinically observes these Dickensian characters without emotional engagement with them or signs of empathy. It is precisely this sense of detachment that gives many of the faces in the exhibition a somewhat eerie silence as the sitters stare out at the viewer.

Unlike many an artist who sided with the poor who lived on the fringes of society, Dempsey simply objectifies his subjects; there is a matter-of-fact quality in his depictions and a certain sameness in the expression of the eyes for most of the sitters. It is a fairly depressing cross-section of society that is in marked contrast to the glitter and glamour that was so frequently depicted by the academic artists of the time. Hansen's assertion that, "Dempsey's people are a small but profound addition to the canon of British art" may be contested, but the beautifully presented exhibition does not fail to make an impact.

As in all miniature art, the attention to detail is impressive, but not unexpected. When John Lumsden Propert published his landmark A history of miniature art. With notes on collectors and collections (1887), he wrote a characterisation that seems appropriate to this exhibition. "The Regent diamond or the Koh-i-Noor is small in comparison with the paving-stones on our highways and almost infinitesimal in juxtaposition with the boulder on the mountainside, but they are certainly not insignificant, and the power and light condensed within their small circumference may be justly compared with the force, life and truth, concentrated by the hand of a master on an inch or two or paper, vellum, or ivory."

John Dempsey's little Regent gemstones shine a light on individual characters that reflect poverty in urban England. The realism of detail makes some of the faces difficult to forget.