If you are a regular tea drinker as I am, you will notice that your mugs and cups over a period of time need deep cleaning. I was taught many years ago by a friend called Jean who was a cleaner at the place I worked at the time, that the best way to clean your china cups/mugs or pottery mugs is to put a teaspoon full of biological soap powder into the bottom of the cup/mug pour on boiling water and leave overnight. Next morning wash as normal and the cups should come up lovely and clean. This method of cleaning the mugs, works every time for me. But it also preserves the integrity of the glaze. I believe that a lot of people used to pour bleach into mugs/cups with boiling water. The only draw back with this is that it eats into the glaze of the piece eventually.