The most talked-about art book of the year Sunday TimesIt will change our views of Western painting London Review of BooksHockney has utterly transformed the scope and basis of the debate... He is making us look at things afresh Martin Kemp, University of OxfordHockney is a superb communicator, his prose as lithe and vivid as his own pencil line GuardianSparkling, brilliantly analysed treatise on the use of optics in art and one of the most important books on painting published in the last 100 years State magazine Secret Knowledge created a sensation when it was first published. David Hockney's enthralling story of how some of the great works of Western art were created with the help of mirrors and lenses and how the optical look came to dominate painting attracted major media attention around the world and generated intense debate in the fields of science and art history. Now in this expanded edition, Hockney takes his thesis even further, revealing for the first time new and exciting discoveries. Hockney's voyage of discovery began when he became gripped by a desire to find out how the artists of the past had managed to depict the world around them so accurately and vividly. As a painter faced with similar technical problems, he asked himself: 'How did they do this?' For the next two years, he sacrificed his own time as an artist to follow this mystery trail, obsessively tracking down the hidden secrets of the Old Masters. As news of his controversial investigations spread, he enlisted the support of scientists and art historians worldwide. In Secret Knowledge, Hockney recounts the story of his quest as it unfolded. He explains how he uncovered piece after piece of scientific and visual evidence, each one yielding further revelations about the past. With the benefit of his painter's eye, he examines the major works of art history and reveals the truth of how artists such as Caravaggio, Velazquez, van Eyck, Holbein and Ingres used mirrors and lenses to help them create their famous masterpieces. For this new edition, Hockney demonstrates, with the aid of drawings, paintings and photographs of his own experiments, how Renaissance artists used mirrors and lenses to develop perspective and chiaroscuro - radically challenging our view of how these two foundations of Western art were established. Hundreds of paintings and drawings - among them the best-known and best-loved works in the history of Western art - are reproduced and accompanied by Hockney's infectious and enthusiastic descriptions. His own photographs and drawings illustrate the various methods used by past artists to capture accurate likenesses, and present the results they would have achieved. In addition, extracts from the many historical and modern documents that he uncovered offer further intriguing evidence, while correspondence between himself and an array of international experts provides an exciting account of the remarkable story as it happened. Secret Knowledge is not just about the lost techniques of the Old Masters. It is also about how we see, treat and make images in an age of computer manipulation. Taking nothing for granted, questioning received ideas and practice, Hockney opens our eyes to the way we perceive and represent the world - a privileged insight into the history of art by an outstandingly prolific and original artist.