Pro tip: baking soda scrub beat my fancy mug cleaner on coffee stains
I have a stoneware mug from a pottery fair in Madison that got a brown ring inside it about 8 months ago, and I tried one of those store-bought mug cleaning powders for a solid month with no luck. The powder cost $9 and the ring barely faded, so I got annoyed and tried plain baking soda with a little warm water instead. I made a thick paste, rubbed it on with my thumb, let it sit for maybe 10 minutes, and the ring lifted off in one rinse. The powder is gritty and takes real scrubbing, but the baking soda paste dissolves the stain and rinses clean without scratching the glaze. I've done this on 4 mugs since then and it works on tea stains too, even the old gray ones near the rim. The only thing I'd say is don't leave it on too long or it dries into a crust that's annoying to rinse. Has anyone tried this on a mug with a hairline crack where stain has crept into the line itself?
Man, I feel your pain on that $9 powder letting you down, nothing stings quite like a cleaner that costs real money and does nothing. I have a mug with a hairline crack near the rim too and the stain in that line is stubborn, so I get why you're asking. In my experience the baking soda paste helps a little on the surface of the crack but it won't pull the stain out of the inside of the line, your mileage may vary though. Take it with a grain of salt since I haven't tried anything stronger than a toothbrush on mine.