A woman came to me at a show, pointed at this engraving and asked why some barns were painted red. I was a bit embarrassed to admit I didn’t know. The search engine DuckDuckGo was most helpful.

Seems that hundreds of years ago (long, long before Home Depot) many farmers would seal the wood on their barns with linseed oil, an orange-coloured oil derived from the seeds of the flax plant. To this oil, they would add a variety of things, most often milk and lime, but also ferrous oxide, or rust. Rust was plentiful on farms and because it killed fungi and mosses that might grow on barns, it was very effective as a sealant. It turned the mixture red in colour and, Voila! a Red Barn.