Why is Criston Cole using a lemon to polish his sword on House of the Dragon?

In the most recent episode of House of the Dragon, Alicent Hightower (Olivia Cooke) walks into the quarters of Ser Criston Cole (Fabien Frankel). He has his sword laid out in front of him, propped on by a box and a couple of books. He appears to be polishing or cleaning the sword. Oddly, he's making use a lemon wedge.

Are lemons or lemon juice actually used to clean swords? There is some evidence. On YouTube, the bladesmith Walter Sorrells uses a lemon juice solution to polish a Japanese blade called a tanto that he forged himself. On his webpage, military antiques specialist Matthew Forde talks about using lemon juice to break up residue left on the brass handles of swords. The website Medieval Collectibles also recommends applying a light coating of lemon juice to wooden sword handles to prevent cracking.

Lemon juice is actually a mild bleaching agent, so in theory it could be used to get stains out of steel swords. Criston has been putting his sword through the ringer lately, cutting off Lord Darklyn's head at Duskendale and probably getting it covered in dust and dirt during the Battle of Rook's Rest, where Criston spent a lot of time unconscious as dragons tangled on the ground and in the air.

Lemons only grow in warmer climates, so you wouldn't find them in the North or even the Riverlands. Criston is from the arid deserts of Dorne, a part of the Seven Kingdoms which may be more hospitable to lemons. So him using a lemon on his sword is actually a neat little character detail; not all the knights in Westeros would know this trick, since a lot of them have probably never seen a lemon before. Maybe Criston can teach them a thing or two. We know he know he expects the other knights of the Kingsguard to keep their cloaks clean. That likely applies to their swords as well.

Criston will be back next Sunday night on another new episode of House of the Dragon, airing on HBO and max.

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