is the process of applying some type of solvent-based polymer that
penetrates the surface of a wood item in order to highlight its natural
beauty and aid in its resistance to degeneration. Usually this means applying a coating, but can
also mean rubbing in an oil or wax that leaves the surface of the wood
accessible to the touch.
The solvent could be anything - turpentine, naptha, mineral spirits,
amyl acetate, xylol, water, alcohol, to name a few. It's important to
know which uses what because they're usually incompatible and one
coating when put over another different one will often react
unfavorably with it.
Staining is the process of altering the color of the wood
by applying either pigmented solutions that distribute ground up
pigments evenly over the surface of the wood or dyes that penetrate the
structure of the wood to alter its color. Both of these are done prior
to finishing and must be chemically compatible with the chemistry of
the final finish.
Another part of wood finishing is "rubbing out" the
finish. This is a secondary operation of sanding down the completed
coating with ever increasingly finer abrasives until a desired
reflective luster is achieved, from satin finish to high-gloss finish.
This requires a physical technical ability distinct from the chemistry
These are "drying" oils that have been dissolved in a solvent so
they're easy to apply and soak into wood. They have added chemicals
that speed up the reactivity of the oil with oxygen to form a hard
polymer (called polymerization) that doesn't come off on your hands. It
"dries". But actually it is more accurate to say that it "cures" -
changes from a liquid to a hard substance. The advantage to oils is
that they are a "penetrating" finish that penetrates into the cellular
structure of the wood, encouraging the play of light in that structure
that brings out a natural luster of the wood, but they do not form a
coating so you can feel the texture of the wood itself. Because they've
penetrated the cells and hardened into a polymer within them, the wood
is resistant to staining. But, they're not very resistant to abrasion,
and should be re-applied every year or two.
There are many kinds of waxes. They all get rubbed into the wood,
whereupon they "harden" through their reaction with oxygen. They are
very similar to oils in that they penetrate and are not really a
"coating", but they allow the wood to be buffed to a higher luster than
oils. They are not very "protective" of abrasion, heat, or spillage,
but they are beautifully visually "soft" finishes.
These are similar to oils and waxes, but suspended in a solvent that
allows them to be brushed or sprayed onto the wood surface and remain
as a thin coating. The solvent evaporates, leaving an even thinner
coating of thick liquid material that gradually reacts with the oxygen
in the air to polymerize into a hard coating. They are very durable,
very beautiful, and very good finishes. Often they are applied in
several coats, each coat adhering to the one below without dissolving
the one below because the curing process of polymerization has rendered
the coating impervious to the very solvent in which it was originally
This is a unique finish. It is a suspension of natural resins in
alcohol. It is a very old recipe but retains its place today because
unlike nearly every other finish it is compatible as an undercoat with
all the others, takes stain, penetrates wood, is easy to apply,
relatively non-toxic, and it's beautiful in and of itself. It has two
drawbacks - one is that the material in the can has a limited shelf
life, the other is that it is easily re-dissolved with alcohol and alot
of furniture has to endure its owners and their guests spilling alcohol
on it. French Polish is a shellac application process.
This is a special group of finishes that, like shellac, the finished
coatings are forever dissolvable in their solvent. This may seem
disadvantageous, but unlike shellac's solvent (alcohol), very seldom
does the owner of the furniture have occasion to spill the solvent
(lacquer thinner, amyl acetate, toluene, xylol, etc) on their
furniture. The advantage to lacquers is that they are put on in very
thin coats, each coat chemically melding with the one before, making a
single-layer coating. This process allows a thorough flat-sanding
between each coat of ever-increasingly fine abrasives during the
application process, resulting in an exceedingly high-quality
single-layer coating that is very flexible, has excellent adhesion to
the wood, penetrates the wood deeply bringing out its natural luster
more readily than any other coating, is the flattest smoothest and the
least "coated" look of all the coatings. Lacquers are time-consuming,
but are used on some of the highest quality works.
This group of finishes can be categorized as "catalyzed" finishes,
meaning that a small amount of catalyst is added to the liquid coating
prior to application. This catalyst greatly speeds the curing time of
the finished coat, as well as adding durability and hardness. These
coatings are often applied so thickly as to require only one coat - so
they speed up the finishing process for the shop doing the work.
They're not particularly penetrating, so the natural lusters of wood
are not accentuated by these finishes. However, for durability and
abrasion resistance, they far exceed the finishes I've mentioned prior.
There are Polyurethanes, which are varnishes and covered in the varnish
description above, but there are also an entire group of urethane
finishes that have been developed by the automobile industry to coat
vehicles. If ever there were a test for the durability of a coating, it
would be a car. They retain their gloss, their corrosion protection,
their all around integrity far longer under far more duress than nearly
any other situation. They are usually catalyzed, and require a
professional setup to spray on. They can air-dry or bake dry. Either
way, they are enduring, though like polyesters they somewhat mask the
natural beauty of wood.
These are high in abrasion resistance, high in chemical resistance,
high in UV resistance, and can be applied in very thick coatings.
They're not particularly good looking, but that is not their primary
Powder Coated Finishes
- These are all finished by baking in a big oven at really high
tempuratures, so they're not applicable to wood. However, they're great
for metal. They are initially applied to the completed work by
statically charging the work and spraying a cloud of powdered coating
material near the charged work. The work attracts the powder like a
balloon attracts dust. When the powder has deposited itself thickly
enough over the work, the entire piece is put into an oven and baked
for a half hour or so. This melts the powder grains together to form a
coating. The advantage to this that an even-thickness coating can
controllably be applied to complex pieces without drips or dry spots.
The chemistry, color, and luster of the powder coating material can be
adjusted by the manufacturer for optimizing whatever characteristic the
fabricator desires. These finishes are the most durable finishes
regularly available. They are not excessively expensive, but they very
seldom can be applied in one's own shop.
This is one of a series of marquetry pieces we produced framed in wood with a black
lacquer finish. Finishing a piece like this requires patience and an