Like Ray said you really dont "need" any extra finish on IW but if you want to reduce the "darkening" caused by light/oxidation get some of the spray on finish with UV protection. If you can find "fix it", which is a spray on clear pottery finish it works very well. You simply spray it on, let it dry, and lightly buff. Its very hard to find and may be out of production though. There are a couple other over the counter spray on finishes that help prevent darkening, best thing to do is buy a few and experiment to find one that works best for you.