Removing stains from cracked dishes

I have some glazed mugs (maybe made of ceramic?) that I love, but the glaze on a couple of the mugs has hairline cracks that have been stained by tea. Does anyone know how to remove these stains? I've tried vinegar, hydrogen peroxide and oxyclean (separately, of course) and none have worked.

Thanks!

Have you tried denture cleaner? Seriously. From time to time, I fill my coffee/tea mugs with really hot water, drop in a tablet or two and wait about ten minutes. The stains then scrub out very easily. This little trick also works wonders on the glass carafes many of us use for coffee as well. They come out looking sparklingly clean, almost new.

Another methode is to use dry dishwasher soap.

Starting with hot water, in a bucket etc, disolve as much of the dry soap in the water, as it will hold. That is, when the dry soap will not disolve, you have enough. Soak the item in that mixture for a day or so.

Works every time.