Alum pickle

Now that the subject is on the table, does anyone has a pickle
recipe using Alum? 

GRANNY’S SUN-DILLS
Med. to lg. cucumbers, whole or cut in halves or spears

3 tbsp. vinegar
2 tbsp. pickling salt
1/4 tsp. alum
Garlic cloves (optional)
Hot pepper pods (optional)
Heads of fresh dill weed

Put vinegar, pickling salt, alum, dill and garlic or pepper pods,
(if wanted) on bottom of quart jar. Pack cucumbers in jar and set in
bright sun for up to a week. Make sure lids are tight on jars before
storing in cool, dry place.