Iron solute

Iron solute is the 18th clue. It is a Lucian clue and was located in Paris, France.

History
Benjamin Franklin was the Lucian in charge of hiding this clue. He wrote a book under the alias Richard S. This books gave more clues on how to find the clue however, there was a card that read:

RESOLUTION

The fine print to guess,

Seek out Richard S_____.

It was eventually figured out that resolution is actually an anagram for iron solute.

Iron solute
Iron solute is iron (Fe) dissolved in water. Iron solute is mainly used for chemistry, metalworking, and is commonly used in ink.