Brewing Black Walnut Dye, or Brou de Noix

In Adventures in Wood Finishing (The Taunton Press, 1981), master finisher George Frank relates that when he was a young apprentice in France, his master’s wife brewed a walnut dye using walnut hulls.  “She filled a large earthenware pot with them, covered them with rainwater and added a pinch of caustic soda.  Then she put on the lid.  For two or three days she simmered this pot on the stove, never boiling the mixture.  Finally, she strained the liquid through a linen cloth and bottled it.”

In the fall of 2015, I decided to follow Frank's account and brew some walnut hulls myself.  My first task was to determine precisely what "caustic soda" was.  It turned out to be lye.  My local pharmacy didn't carry it, so I went to a hardware store.  First the clerk and then the manager asked me why I wanted to buy lye.  I explained.  The manager laughed and commented that they had some, but these days lye is kept under the counter.  Apparently, it's in demand for cooking meth.

The next step was to harvest the walnut hulls. The walnuts of Juglans nigra, the common black walnut, are enclosed within a greenish hull that, after dropping from the tree, rots and turns black.  I waited until a number had fallen in early October, put on gloves, and quickly gathered a pail full.

Back home with my harvest of hulls, I filled our slow cooker two-thirds full of hulls and then added enough distilled water (rainwater would also work) to fill the slow cooker to capacity.  I wasn't entirely certain about what a pinch of lye would amount to, so I measured out a half teaspoon and stirred it in.  After covering it, I simmered it for twenty-four hours.

Not having any linen I wanted to turn dark brown, I used folded cheesecloth to strain it.  I then decanted it into a clean plastic juice container and labeled it. 

I've only had occasion to use this Brou de Noix once, but it does work.  You can dilute it with distilled water or rainwater if you don't want so dark a color.  Conversely, additional coats will darken the wood somewhat.  As it's water based, it may well raise the grain, so be prepared for the need for whiskering.

Chemically, according to Wikipedia, this dye is effective because black walnut hulls contain juglone (5-hydroxy-1, 4-naphthoquinone), plumbagin (yellow quinone pigments), and tannin.  The tannins act as a mordant in the dying process, helping fix the color.

Bottom line?  Brou de Noix costs almost nothing.  It's simple to make, and the process is rather fun.  In a small way, when you make some you become part of a tradition of craftspeople extending back into the Middle Ages.  That's a good feeling, I discovered.  You might enjoy it, too.