Chez Chef boasts a tiled hallway, made up of lots of little tiles in a mosaic pattern, such as is to be seen in quite a few bars these days. As it has been in constant use for the last hundred years or so it is ingrained with grime. How do I remove the dirt without damaging the tiles or exposing them to worse future damage? (When they cleaned the terra-coota tiles on the Albert Hall they found that the encrusted dirt had been protecting the tiles, and stripping that and some of the glaze off left them worse off then before) I don't want to use abrasives, or chemicals, as one will deffo cause damage, and the other I don't know enough about, but hopefully someone here does. Currently it is swept, and mopped with fairy liquid. If there are any 'Dos' or 'Don'ts' or other advice, I would be grateful. Ta muchly.