Place olives in a large jar or plastic container with plenty of water and salt Leave for one or two week. Olives must stay submerged in the water the whole time.
After 2 weeks empty the liquid and wash olives well.
Fill container with water to cover olives again.
Change this water every day for 2 more weeks the more changes of water the less bitter the final result
Finally drain, salt lightly and store in jars with light vinegar and little oil
Herbs like oregano, and thyme may be also added.
Green olives need more to remove the bitterness than the ripe black ones. Fruit can be left in the brine for up to 6 months if necessary.
A black film could form over the surface after a time, but just skim it off. It is harmless. Once the olives are placed in the marinade they will continue to improve with time.