Hey Borek,
Thank you for taking the time to reply to my post!
The liquid isn't super important - just looking for something that is safe to handle without some hardcore hazmat gear.
As for the concentration - the more iron the better.
Long story short, I made a ferrous acetate solution that was perfect - in terms of what I was trying to get it to do (react with tannins).
The solution was clear when made, and clear when I bottled it into a sealed plastic bottle.
After a few hours, I noticed the solution starting to turn orange/brown in color - I bottled the same solution into multiple bottles, and noticed that each one has a slightly lighter or darker orange/brown tone to it.
So, the color issues is something I am trying to avoid.. Also the smell of acetic acid would be awesome to avoid if possible.
I'm simply looking for a liquid that is odorless/colorless and has a high concentration of iron.
Any thoughts?
I appreciate the input!