Iron

Iron (Ferrous Sulfate).  Iron will darken and sadden depending on the amount of iron used.  Because iron can weaken, it is added after the fiber is soaked. 

These are two jars, Elm Bark and Red Onion with 10% per the weight of the wool (3/4 tsp of iron each).

'

The problem I had was Soaking the wool.  I'm worried the iron batch bled onto the unmodified batch.