36 Ammonia Fuming: How does the fuming process differ from staining?
Description
This article is from the Woodworking FAQ Collection 1, by multiple authors.
36 Ammonia Fuming: How does the fuming process differ from staining?
First, the brown color is produced by reaction with ammonia vapor and
requires no contact of any liquid with the wood (other than an application
of clear finish, later ). No brushing, streaking, dripping, dipping or
wiping is involved. Second, the fumed color often extends much more deeply
into the wood (especially in comparison to solid-pigment stains), and depth
of coloration can be as much as several millimeters (1/8"). Furthermore,
with quartersawn oak, the ray-fleck features are colored by the fumes yet
retain a muted contrast with the rest of the wood, yielding results
distinct from the high contrast produced by a solid-pigment stain. Finally,
unlike staining, ammonia fuming offers a limited range of color(s).
Depending on the duration of fuming and the wood properties (tannin
content) the color can range from light brown to chocolate brown/black.
Since there can be sapwood/heartwood variations in tannin level, the
intensity of the developed color may show some variability (as can happen
with stains) which is minimized--but might not be eliminated-- if the piece
is constructed using wood from a single tree. Color intensity variations
resulting from fuming may be further minimized by subsequent touching up
with stain or by direct application of ammonia solution to the lighter
parts.
Take care not to overdo the fuming, inasmuch as the depth of color (i.e.,
penetration) will make it nearly impossible to correct. Err on the side of
"too little", as it's easy to resume fuming to intensify the color.
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