It's a blog! Mainly of book reviews.
As I pass the 4/5ths mark and start Part IV, Gawain anxiously awaits the dawn of New Year's Day, understandably failing to sleep much. He gets up and gets dressed to find his armour gleaming and rust-free. It's been "rocked" - put in a barrel of sand then rocked around. This removes rust, of which there was no doubt plenty, having ridden around the dismal wilderness for the entire autumn season, wearing it.