"Do you have any ideas?" you ask yourself and, by extension, the goblins. You wait for a response, but all you get is a nagging feeling that they would have you try to cover the blade with something. You don't know much about the nuances of the aura-communication, so you take that as an answer.
Looking around, you find several different dusts on the counters, but they refuse to stick. You walk over to a tub of... well, it may have been water at some point. Now it has been fouled over the years with metal debris, crumbs, and a large variety of mosses and fungi. You assume that it is used to cool the blades of swords when they are ready to be used. You dip the knife in, but are disappointed. The metal reacts with whatever was in the water, clearing it of all impurities with a beautiful blue light. What remains is a tub, perfectly clean, filled with pure, fresh water.
Even though this on its own is miraculous, it still doesn't help you cover the blade.
Deciding on a different approach, you cut out a block of stone a little larger than the blade out of a nearby boulder. You shove the knife into the block and tie it down with some cloth that was also discarded nearby. You ponder momentarily why, exactly, there are so many random materials here, but are interrupted by something touching your hand. It's the knife, which has apparently freed itself of the block of its own will and returned to you. It takes you a moment to process this.
This gives you an idea. You throw the knife to the best of your ability at the opposite wall, and it gets lodged in the stone. You wait for a moment, but it stays where it is. Getting impatient, you turn to examine the block to get a more reasonable answer, but the very second you avert your eyes you are holding the knife again.