Preheat oven to 350F.
In a medium-sized roasting pan, roast bones, onion, carrots, celery, and garlic for 45 minutes.
Add to slow cooker.
Add spices, salt, and apple cider vinegar.
Cover with water and set on low for 24 hours.
Strain with a mesh strainer and let cool for an hour before refrigerating or freezing.