That's a very pretty saber, even if it has been coated. I've seen a lot of antique tools (chisels and such) with shellac painted on the blades by antique dealers. I also had a Parker shotgun in my possession for a while that had been coated with shellac. I suppose this was done to prevent rust, but it's a clumsy way to go about things. I expect the saber was coated by someone well after the original owner. We'll never know, though. You could gently clean that coating off and then wax the blade. If I were going to attempt it, I'd use alcohol first. It'll dissolve shellac. If it doesn't work, try lacquer thinner. Then maybe acetone. Shop towels or cotton balls only. NO ABRASIVES! Keep the chemicals away from the grip, too. If you do this, use good ventilation and rubber gloves.