Put your oil glasses in a large washing cup filled with water and let it sit in the water for a few hours and then take them out and hard wipe each one until their dry and ready to be put away
What kind of wick/supports do you use? I use the metal tubes with a base that keep the wick in the center of the glass and have never had problems with burn stains at all. Also, don’t put a layer of water under the oil as the sputtering also causes stains. And floating wicks especially are a recipe for disaster.