I have always used the 50/50 ration for vinegar baths to remove rust. However I recently had a lodge lid that would not come clean (deep black shadows with rust below) no matter how many soaking and scrubbing sessions I did. Finally I just submerged it in straight vinegar in the sink 30 minutes later it looked new. I know vinegar will deteriorate cast iron if it soaks to long but is there a danger from short soaks in straight vinegar?