Publisher Walter Blackie commissioned the house in 1902. Mackintosh planned it as a complete work, from the shape of the rooms to furniture and textiles, with Margaret Macdonald helping create the interiors. Outside, he wanted something spare and startlingly modern. Portland cement roughcast seemed like a wonder material. It promised a clean surface and protection from weather. The Blackie family moved in in 1904. But Helensburgh’s rain kept finding its way through. The cement did not let the walls shed that moisture properly. Over decades they became saturated and began to crumble, while damp threatened the interiors. Conservators eventually described the house as “dissolving like an aspirin in a glass of water.” Saving Mackintosh’s masterpiece had become a strange problem: one of his boldest material choices was helping damage it. So in 2019, instead of hiding the house behind ordinary scaffolding, the National Trust for Scotland built another structure around it. The Box uses 165 tonnes of steel and 8.3 tonnes of chainmail. Rain is kept off, air can still move through, and walkways carry visitors around the walls and above the roof. The aim was not to repair quickly. It was to let the building dry slowly enough to avoid doing more harm.