According to new archaeological evidence, human beings have been using paint for 100,000 years.That means it was already a very old medium by the time of the cave artists at Lascaux. People still are trying to find new things to do with pigment and brushes.Frank Stella (born 1936), whose works feature in a medium- sized retrospective, with many on sale, at Haunch of Venison (6 Burlington Gardens, W1, through Nov. 19), once said he aimed to keep the paint on his work “as good as it is in the can.”Indeed, the U.S. artist’s best work depends on what Damien Hirst has called the “yumminess” of paint: the fact that it is attractive stuff, much more sensually alluring than a photograph. During his early phase in the late 1950s and ‘60s, Stella painted mainly stripes, and not the wallpaper variety. These are stripes that sizzle with energy, arranged in dynamic v-shapes, deltas and hexagons. Often they are painted on geometrically shaped canvases, effectively becoming flat sculptures hung on the wall.The best work in this exhibition is the huge “Basra Gate I” (1968), arched like a protractor from a geometry school set. It’s dynamic, direct, simple, yet so forceful that it takes you over while you look at it. As time went on, Stella’s works tended to become more and more 3-D. They also became messier and more complicated. Contrary to F. Scott Fitzgerald’s line about American lives, there has been a second and third act in Stella’s career; the first, though, was definitely the best.Francis Bacon (1909-92) was bored by abstraction, which he thought of as just pretty patterns or shapes, but he was obsessed by the way in which a brush stroke can seem to metamorphose almost magically into an object in front of your eyes. An enterprising exhibition at Ordovas (25 Savile Row WI, through Dec. 16) puts portraits by Bacon beside a Rembrandt.The U.K. painter was fascinated by this odd, possibly unfinished, picture -- “Self-Portrait With Beret” (circa 1659) from the Musee Granet in Aix-en-Provence, France. In this painting, Rembrandt’s face is a gnarled knot of paint, with the eyes stuck in like pieces of coal in a snowman’s face. Still, the Dutchman’s familiar battered visage and drinker’s nose emerge.Bacon attempted to use similar blobs, smears and spatters of paint to create a sense of heaving, often menacing life -- what he called “the brutality of fact.” On a good day, especially in the late 1940s and early 1950s, he succeeded: Some of his pictures are downright frightening. As he grew older, the distortions turned into mannerism. As a result, this juxtaposition with Rembrandt is more revealing than flattering to Bacon. In his case, too, the first act was the best.Paint seems to be retaining its appeal in the 21st century. Wilhelm Sasnal (born 1972), is a Polish artist whose work is on show at the Whitechapel Gallery, London E1 (until Jan. 1, 2012). He is, on this evidence, interested in all sorts of things you can do with paint. Many of his works are based on photographs, often found on the Internet. Sometimes these images break up into a mass of those non-rational brush marks that Bacon talked about.The exhibition is uneven. Yet Sasnal is clearly an artist to watch. One of his best pictures is also one of the latest: “Pigsty” (2011), is at once banal, sinister -- the animal houses suggesting the huts of a prison camp -- and monumental.