Why are barns generally painted red?
Presume you mean in the US? There was a kind of tradition for red barns, which was imported to the US from Europe. Traditionally, the wood was treated with linseed oil, mixed with blood (from recent slaughter). Later, farmers added ferrous oxide (rust) to the oil mixture. This inhibited fungal growth and preserved the wood, and (coincidentally) gave the wood a dark-red tinge. It became fashionable to have red barns, and this tradition moved to the US from Europe. However, when paint became widely available in the US, bright red was the cheapest available, so most barns were painted bright red, except for those whose owners could afford to buy the more expensive white paint.
