The first thing to remember when trying to clean a Claret jug, or similar glass container, is that there is a difference between dirty glass, and cloudy glass. Cloudy glass is a good sign that the glass is original, as old glass has more impurities than its modern day counterpart. Dirty glass on the other hand is often just limescale collecting on the surface of the glass. A good way of cleaning this is to add a limescale remover, we use Viakal, and then to fill the claret jug with cold water. Leave this solution overnight, and then the next day pour it away. If the glass still looks dirty you can repeat the above. When the glass looks clean, add a little methylated spirits into the jug and leave for a few hours. This will act as a drying agent to stop the limescale from reforming. Pour the meths away, and the claret jug should be clean and dry. REMEMBER to then wash the claret jug or container well before using!