I recently discovered an amazing archive of dyed fabrics created by the Japanese scholar Uemura Rokuro (1894-1991). He made all the swatches with natural dyes, combining them with different mordants.

I found some examples of logwood, the dye brought from America by the Spanish monarchy:

1. logwood with lime water

2. logwood with alum, and a small quantity of vinegar

3. logwood with copper (left) and with chromium (right)

4. logwood with iron (right swatch)

He made side notes about every dye. For the logwood, he wrote that, without a mordant, the color is a reddish brown. Only with different mordants can you get the darker colors. Iron is usually the one that makes brown dyes and inks turn black.

Learn more about the difficult task of dying in black in the link below.