“As far as I am concerned the paint is the person. I want it to work for me just as flesh does.” Lucian Freud's almost mystical description of the link between the portraitist, his materials, and the sitter is more pertinent than ever in the digital age. The reproducibility of the photograph was, at the beginning of the 20th century, perceived as a threat to the painter. In the first decades of the 21st century, the sheer profusion of digital images has provoked a movement back to the physical—what critic Simon Jenkins has called the “cult of authenticity”. The National Portrait Gallery's Lucian Freud Portraits, which showcases the artist's work from 1940 until his final painting Portrait of the Hound (left unfinished when he died in 2011), is nothing if not authentic. The paintings not only evoke the personalities of the individual subjects: they also say something about the relationship of Freud to his sitters, the studios in which they were painted, and the nature of the human body itself. The earliest works show that Freud's preoccupation with the human animal was there from the start. Backdrops are sparse: props such as flowers or animals are, like the sitters, solitary and separated from their natural surroundings. The brushwork is smooth and precise, verging on the hyper-realism of the now almost forgotten portraitist Meredith Frampton. It was when Freud relinquished sable brushes for coarser hog's hair brushes in the mid-1950s that his style came into its own. With a bolder stroke, he explored what was to be an enduring obsession: human skin. Frequent remixing of his paint brought out complexity of colour and texture in even the flawless skin of a child in Baby on a Green Sofa (1961). At the other end of the human lifespan, Freud captured the coarsened, ruddy features of photographer John Deakin with an unflinching eye. This image of a man suffering the effects of years of alcohol use would not be out of place in a medical textbook. The connection between the human body and the natural world is examined through the juxtaposition of models with objects or animals that mimic their forms and, perhaps, characteristics: a nude woman with a bisected boiled egg, or a man and a rat. As Freud said, “I am inclined to think of ‘humans’…if they're dressed, as animals dressed up”. A later work, Naked Portrait Standing (1999–2000), explicitly remarks on the resemblance between a female torso and the trunk of a tree, as portrayed by John Constable in Study of the Trunk of an Elm Tree (c. 1821). The set of paintings of Sue Tilley (1994–96) go further still: in the rolls and curves of flesh, we see the human body painted as a landscape, reminiscent of contemporary work by younger artists such as Jenny Saville (Strategy, 1994). Collected in a small side-room, the portraits of performance artist Leigh Bowery are intriguing; shorn of his flamboyant costumes, Bowery's physical robustness and dramatic poses belie his difficult relationship with his own flesh, and his serious illness with HIV/AIDS. Girl Sitting in the Attic Doorway (1995), a picture of Bowery's wife Nicola Bateman around the time of his death, is a compelling image of bereavement. Indeed, Freud was as adept at portraying the psychology of his subjects as their bodies. He saw the vulnerability in Francis Bacon's lover, George Dyer, more famously depicted as a force of chaos in Bacon's paintings. The scope of this exhibition also means that the viewer gains a sense of the effect of the passage of time. The three pictures of Freud's second wife, Caroline Blackwood, show the transition from innocence (Girl in Bed, 1952) to a more careworn, alienated expression (Hotel Bedroom, 1954) over the course of just 2 years. The portraits of his mother, from the nadir of grief over the death of her husband to a more serene acceptance, reveal Freud's understanding of the interaction between time, experience, the body, and the mind. This is an unmissable exhibition: though the artist has gone, his physical presence remains.