1. Place radish slices into a pint-sized jar with a lid.
2. Heat vinegar and water in a small non-reactive saucepan over medium heat
3. Whisk in sugar and salt until just dissolved.
4. Remove from heat and add cumin seeds, and black peppercorns.
5. Let cool slightly for 5 to 10 minutes.
6. Pour liquid over radishes till completely covered.
7. Let cool to room temperature, then refrigerate overnight.