At the opening of a new exhibition hall in the Polish town of O?wi?cim last week, a curious crowd of visitors seemed impressed with the purpose-built architectural structure: a minimalist, Aldo Rossi-like building that feels more like a tomb than a gallery. They initially remained more sceptical of the artworks inside, however. “Is it a painting or not?”, some people asked each other. “Take a closer look – can you make out what it’s made of?” Obscurity is in the essence of German artist Gerhard Richter’s Birkenau cycle, arguably the single most important artwork by one of the most influential...