First thing is to clean the cup thoroughly. This is easily done with either bleach and water, or denture tablets and water, and the cup should be allowed to soak in either solution overnight. This is to remove any stains within the crack.
Next you're going to have to identify if the pattern on the cup (I'm assuming it's decorated, as most Queen Anne cups are) has been compromised. If it has, you're going to want to pick up some good paints and a couple of fine artists brushes and touch up any nicks.
Finally you're going to want to coat the entire cup in some sort of silicone or other sealing agent. I recommend the spray-on varieties, available in most hardware and craft stores, because they're a lot easier to use than the paint-on ones.
FYI: All good china should be soaked in water for 24 hours at least once a year to allow the porous materials within to reabsorb moisture, which will prevent them from becoming brittle and cracking.
handygirl, November 2008
