In my elementary school, the janitor was a shadowy character who mostly stayed in the basement, in his private area next to the boiler room. Yet he was powerful enough to make everyone (even teachers and the principal) remove their shoes when he waxed the gym floor. And he had a collection of chemicals to clean up any mess, even the ones Rickie Hensel made when he threw up during biology films. He came to mind the other day as I headed to the hardware store to get some “janitorial strength” ammonia.
I’m making an assortment of layout tools, and as I prepared a quartersawn white oak straightedge, the idea of giving it a fumed oak finish lodged in my brain. The problem was that my straightedge was too small to justify building a tent, and too big to fit in any of the airtight containers we had around the shop. I began to wonder if “Janitorial Strength” ammonia would color the wood if I wiped it on and let it dry. Just as my project was an in-between size, this stuff is stronger than household ammonia, but nowhere near as nasty as what I use for fuming. The picture above shows the result of wiping white oak with a rag, and keeping it wet for about an hour.
Before coloring, I wet the wood with distilled water, allowed it to dry overnight, then sanded it down with #320-grit sandpaper. This step kept the ammonia solution from raising the grain. The resulting color was close to the same disappointing grey you see when fuming, maybe a shade or two lighter. When the wood is dry, the chemical reaction that makes the color change is done. You don’t need to neutralize it with anything. I just lightly rubbed with a nylon abrasive pad before applying a top coat. Ragging on a coat of amber shellac brings out the color. Additional coats of shellac will continue to darken and tint the piece, and black wax will turn it dark brown. I was happy with this medium brown color, so I only applied one coat of shellac.
Here is the difference between an unfinished piece of wood (from the same board as the finished piece) and the end result. Most hardware stores carry 10-percent ammonia, and you do need to exercise caution when you handle it. Make sure you’re in a well-ventilated area; I recommend taking it outside. Wear some goggles to protect your eyes in case of a splash, and gloves to keep it from burning your skin. And as a bonus, a little ammonia in a lot of water is a great way to clean a shellac brush.
– Robert W. Lang