This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A small portion of hyposulphite of soda mixed with vinegar will make a good cleaner for teacups having tannin stains. This process does not injure the finest china and is inexpensive. The same solution works quite well on clothes that are accidentally stained with tea. They should be washed out and dried quickly after its application in order to make this method most effective. - Contributed by Loren Ward, Des Moines, Iowa.