Stolen and rewritten from here
Sterilize
a glass 1-pint jar
Clean and thinly slice
1 bunch radishes, about a 1/2 pound
and place in jar
In a small saucepan, mix
1/2 c white or apple cider vinegar 5% acidity
1/2 c sugar
1/4 c water
1 t salt
1 t yellow mustard seeds
1/2 t ground black pepper
1 bay leaf
1/2 t dried crushed red pepper
and bring to a boil. Remove from heat and pour over radishes. Put cover loosely on jar, let cool somewhat, and then snug it up. Refrigerate at least one day; can be kept several months in refrigerator.