You can. You can also buy the active bits pre-extracted and ready to dissolve in water to use as a stain as Van Dyke crystals: https://bolgers.co.uk/products/b

You can. You can also buy the active bits pre-extracted and ready to dissolve in water to use as a stain as Van Dyke crystals: https://bolgers.co.uk/products/bolgers-walnut-crystals https://bolgers.co.uk/products/bolgers-walnut-crystals No affiliation on that, they just happened to have a decent description of the product.