If you have a lot of black walnut trees on your property, or have access to them, you can easily make a homemade walnut stain the will cost absolutely nothing. I wouldn't recommend using the stain on fine furniture, but if you are staining homemade wooden toys, small woodworking projects, or just touching up a bit of walnut furniture, it works great.
I used to make wooden rifles that shot rubber bands for my son and his friends. I stained all of the rifles with my homemade walnut stain. I didn't even bother to varnish over the stain finish and they still stood up to the test of time.
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To make the stain, gather a good supply of black walnuts. A plastic 5 gallon bucket is a good choice for putting them in. When picking up black walnuts, it's best to wear gloves. They are almost guaranteed to leave dark stains on your hands. You will need to choose black walnuts that have the outer husks turned from green to brown or black. Don't remove the husks, as they help in making the stain. Fill the bucket about half full of walnuts and husks.
Boil a large pot of water. Pour the boiling water into the plastic bucket. Continue to fill the bucket with boiling water until the tops of the walnuts are completely covered.
Now you need to let the walnuts steep in the water for at least a week. The longer they steep in the water, the darker the stain will become. You may want to put a lid on the bucket to keep children or animals from getting into it.
After a week or two, drain the liquid through a metal colander or wire screen. You may have to do this more than once to get the smaller particles of debris out of the liquid. Once the dark liquid has been well strained, it's ready to use.
Just apply it with a brush or wipe it on with a cloth, just as you would stain bought from a store. If the wood will be exposed to moisture, it's best to cover the stain with a protective layer of varnish or polyurethane. The stain is water soluble, so if it gets wet, it may come off and stain items that come into contact with it.
If you don't need to use a protective coating, you can easily reapply another coat of stain in the future. The stain on the wood may start to lose its darkness over time. For future use, you can easily store any leftover stain in plastic or glass jars with lids. Don't let them freeze or the jars may break.