Over four decades, two collectors put together a gathering of pictures widely recognized as among the world's most important private ones. Spanning the entire history of the medium, it lacks hardly any of the names that forged that history, comprising some of the most famous masterpieces by artists working across generations. A highlight exhibition at a leading museum presents these works, and the accompanying volume presents them in visual confrontations rather than just chronologically, offering a key to their physical quality and inviting readers to question their own individual experience of the medium.