Ammonia fuming

Overview

Fuming exposes wood to ammonia vapour in an airtight tent. The ammonia reacts with tannins in the wood and darkens it. Fine Woodworking says it works best on white oak, beech and butternut, penetrates about 1/8 in., and was used historically by Stickley, Limbert and Roycroft. Fine Woodworking (Rodel) reports the fumed colour is colourfast.

Pros

• The colour goes into the wood, so it is not a surface film.
• Colourfast according to Fine Woodworking.
• A gas treatment: no liquid stain is applied to the surface.

Cons

• Ammonia is hazardous (see Safety).
• Works on tannin-rich wood only; colour varies board to board, so use boards from one tree (Rodel).
• Needs a sealed chamber and days of exposure.
• Penetrates only so far; deep sanding can remove it.

Suitability

White oak, beech and butternut are the named woods (White oak, American beech, Butternut). Poor results on low-tannin woods.

Coats and application

1. Build a chamber. Fine Woodworking: a polyethylene tent on a frame.
2. Choose ammonia strength. Household ammonia is 5 to 10%; janitorial is 10%; industrial is 25% (Fine Woodworking tests). Fine Woodworking compared them on white oak at 72 h: household penetrated ~1/16 in., janitorial ~1/8 in., industrial full depth. Janitorial at 48 h matched household at 72 h; industrial at 48 h matched janitorial at 72 h. Dunton cites ammonium hydroxide for fuming at ~28% versus under 5% household.
3. Use glass or plastic dishes, never aluminium (Dunton).
4. Test on offcuts at 72 hours (Fine Woodworking).
5. Vent, then finish.
6. Dispose by diluting in a large bucket of water (Dunton).

Compatibility

Finish with oil or varnish; see Ebonizing and Lye and chemical staining for other chemical colours. Do not combine ammonia with chlorine bleach. CDC says it reacts with oxidizers, acids and halogens, including chlorine bleach, and says "Do not mix household cleaners!"

Care and repair

Local repairs are difficult because fuming needs a chamber. Small touch-ups use dye and glaze (Glaze and antiquing glaze).

Safety and environment

CDC: ammonia burns the nose, throat, lungs and eyes, causes coughing and can cause blisters. NIOSH: IDLH 300 ppm; REL TWA 25 ppm, short-term 35 ppm; OSHA PEL 50 ppm; corrosive to copper and galvanized surfaces; eyewash for solutions over 10%. Dunton recommends goggles or a face shield, gloves and an ammonia-cartridge respirator. Vent the chamber well before opening it.

Related

• Ebonizing
• Lye and chemical staining
• Wood bleaching