Restoration Workshop: Darkening wood

Using ammonia to darken wood

By Shane Eagen

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The Procedure

Assemble the following: respirator with ammonia filter cartridges, goggles, safety gloves, airtight fuming chamber, glass dish, ammonia (available where cleaning products are sold), bucket of water, wood to be fumed. A glass dish is preferable to a bowl simply because a dish exposes more ammonia to the air and glass won’t react with the ammonia. Arrange the wood in the chamber so that all the wood needing to be darkened is exposed and not touching any other piece. Place the glass dish in the middle of the chamber floor. (If there is a lot of wood to be fumed and the chamber is bigger than a garbage pail, use more than one dish). Because you’ll be working closely with a significant volume of ammonia you should wear a respirator, goggles and gloves. Fill the dish with ammonia and seal the chamber with duct tape.

The intensity of the colour is controlled by how long the wood is exposed. The numbers on the blocks represent hours

To help determine what is happening in the chamber, put some scrap pieces of the same species of wood in the chamber at the start of the operation. These are test pieces that can be removed and inspected periodically. You can also put a coat of clear finish (the finish you intend to use on the project) on the exposed area of the test piece. This will immediately give you a precise reading of the colour of the wood. If it is not dark enough, continue with the fuming process. This is a fairly long process, which means that so long as you do all the pieces that need fuming at the same time in the same chamber, there is no anxiety concerning timing.

The ammonia will stop working after a while, so about every eight hours put on all the safety gear, open the chamber, empty the dish into the bucket of water, refill the dish with fresh ammonia and reseal the chamber.

When the process is finished, put on the safety gear, remove the furniture from the chamber, empty the ammonia into the bucket, put the bucket outside, and remove the safety gear. Allow the furniture to off-gas for a day before applying a finish. Something to keep in mind: Fuming with ammonia does not add a chemical to the surface of the wood. This means that any stain or dye can be used over the fumed colour. Also, any finish can be put on the fumed wood. This allows for an infinite range of colour possibilities.

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