Board Thread:General Discussion/@comment-27338732-20151203212251/@comment-24577221-20151204042731

You don't need 10 instead of 5, but that would almost double your chances with every try.

If you've had 5 torches lit every time you made a breeding try, and you've really done 100 tries, I'm a bit surprised that you haven't been successful. Those numbers would give you a 99.8% chance of getting at least one Ethereal.