Making a lake pigment out of black walnut hulls is the easiest method for me to capture the color in a form that is storable and usable later on. I don't want to have to cook down a pot of walnuts every time I need to color a piece of wood.
What is a lake pigment? In my normal-person-not-a-chemist terms, it is when you take the plant based color that is swimming around in your water dye bath and you bind those plant pigments with something (alum) to be able to filter it out of the water. It precipitates, or binds and forms a solid that you then filter and dry out to use as a pigment in paints or stains.
First, I'm heating up the black walnuts in a bit of water. These are old and have sat rotting and drying for many months. The water quickly turned very, very dark brown.
Next, strain and filter all the bits. Using old ones like this creates quite a bit of mush so it must be filtered well at this stage.
Then put the filtered walnut juice in a jar with a LOT of room left in it. You'll see why.
I dissolve alum (potassium aluminum sulfate) in a tiny bit of hot water in a separate dish and stir it into the jar which binds to the pigment.
Then (and this is the potentially messy part) I add soda ash to neutralize it which makes it foam up and act all crazy so this part is best done over a sink just in case.
Stir it up and the foam eventually calms down and if you leave the jar alone it will separate with the heavy pigment layer on the bottom. In my experience, it completely depends on the batch and plant used how fast this happens. Almost instantly to taking two days.
Then you pour the sludge through some cloth. I use silk but have also tried coffee filters and other finely woven fabrics - avoid cheesecloth or anything with texture though, you'll loose a ton of precious pigment that gets stuck in the fibers and you won't get it out.
I make watercolor paint with mine. Below is just made watercolor poured into a tin and painted onto wood.
Next, the wooden painted sample was placed in a sunny window for a month along with a bunch of other samples to test lightfastness.
I'll share my walnut lightfastness results soon, as well as the different methods I tested - using alum presoak on wood, using soy milk presoak, using a lake pigment, using a regular dye bath, etc.
For specific amounts of alum/soda ash I used the information provided in the book The Art & Science of Natural Dyes.