Collect red cabbage leaves
Chop the leaves into small pieces
Boil the chopped leaves in water for 10 to 15 minutes
Let the liquid cool
Strain the liquid into a clean container
Cut filter paper or coffee filters into strips
Dip the strips into the strained liquid
Remove the strips and let them dry completely
Store the dried strips in a dry container
Use the strips as litmus paper alternatives for testing acids and bases