The term "cloudy glass" refers to glass that has what appears to be a milkish film on it. According to Heritage Auctions, this foggy appearance is caused by calcium deposits. Being washed in hard water is one cause of cloudy glass. Besides looking unattractive, this fog causes antique glass pieces to be less valuable. The cloudiness can be light, medium or heavy. No matter how thick it is, it usually can be removed from the glass.
Fill an antique drinking glass with warm---not hot or cold---water. Hot or cold water can crack or break the glass. Drop a denture tablet in and let it soak for several hours, or even overnight. Pour the solution out. Then, rinse the antique glass clean. Buff it to a shine with a clean, soft cloth.
Follow the above instructions for other pieces, but use a plastic container large enough to hold the individual piece. Fill the container with a few inches of warm water, enough to cover the glass piece.
Clean a light calcium deposit off glass by using petroleum jelly, according to Heritage Auctions. Apply a thin layer all over the glass. Let it set for 4 to 5 days. Then, wipe it off with a clean, soft cloth.
Place a thick towel in the bottom of a plugged sink. Add a few drops of mild dishwashing liquid and fill the sink half-full with warm water. Place a few drops of household ammonia into the water. Clean the antique glass with a no-scratch scrubber to remove heavier calcium deposits. Rinse the glass clean and dry it with a soft cloth.
Remove any stoppers that may be in the antique glass before you clean it, according to the White Friars website (see resources).
Antique glass shouldn't be placed in a dishwasher. Instead, it should always be washed gently by hand.