Cabbage Juice Indicator

Red cabbage juice is a great indicator - it turns pink in an acid, green in a base, and stays blue in a neutral substance.  And while it takes a little time to make, it's a whole lot cheaper than other indicators. 

To make some: 
Chop up a head of red cabbage and place it in a large pan.  Cover the cabbage with water.  Simmer for about 20 minutes (your house will smell like cabbage).

Let the contents cool before you remove the cabbage.  Store the water (now cabbage juice) in a jar*.

To test your cabbage juice:
Set up three glasses:
Pour a little vinegar in the first, some baking soda dissolved in water in the second, and tap water in the third.

Add a few drops of cabbage juice to each glass and observe.

*You can freeze the cabbage juice for longer storage.  Pour it into ice cube trays and freeze.  Then place the cubes in a freezer bag or box.  Pull out individual cubes as you need them.