Saya LacqueringHow to put on a mirror finish
written and illustrated by Thomas L. Buck, Ph.D.
Form & Function - The surface polish of an object can enhance that object's form, much as people express their individuality, or reveal who they are, through clothing or image preferences. Polished lacquer does not only affect our response to a form, it defines the form. A polish's relationship to form can be explored in the same way that an individual's feelings are expressed through language and movement, or timing and grace. Such combinations offer dialects which surpass conventional language, and force a deeper emotional response from the observer.
High-gloss lacquer
finishing on a saya is
time-consuming and
demanding. It requires
precise surface
preparation and a
carefully followed
schedule of application
with constant
examination and
correction along the
way. If correctly
readied, a good lacquer
finish has the quality of a
mirror, if improperly
prepared, it will
unforgivingly reveal
every irregularity in the
surface. It is especially
important to learn how
to judge the quality of
the wood surface before
you apply any |
finish, by
the time a surface defect
manifests itself in the
lacquer film, it's usually
too late to correct it.
Step 1: Preparing the surface - Looking straight into a surface you can pick out obvious flaws like scratches, nicks and holes, but if that is all you do, you miss most of what will become painfully obvious later. To find less pronounced defects you will need to position a light source and your eye so that shadows are created and observable. Imagine a landscape at the moment the sun is setting. The subtlest of features casts a shadow. Once you are in the position to view the topography, you must keep in mind what you did to the surface and anticipate the effects. If you hand-planed the surface, there may be long, sharply defined ridges that follow the path of the edge of the plane iron. A machine sander will produce a more scalloped surface, the radius of the disk arc repeated. Sanding and scraping may yield more varied effects, especially as the density of the wood varies. Sanding removes softer areas more quickly than harder areas. If the wood grain is uneven you can expect the surface to be uneven although you have taken care to work consistently. From the 'sunset' perspective, the relatively dense areas of the wood will stand out from the surface and will reveal shadows following the grain.
When sanding, back up
the abrasive paper with
some hard material -
wood, hard felt, rubber
blocks, or posterboard
for both the flat and
contoured surfaces of
the saya. Your paper
must not be able to
conform to the
irregularities you are
trying to remove. Take
care also to sand |
in line
with the length of the
saya and its curve, and
to release pressure from
the paper at the end of
each stroke, to avoid
swirl marks.
Avoiding the risks of scraping requires more skill. Scrapers work most efficiently on tightly grained or dense wood; softer or loser grained materials compress under the cutting edge instead of standing up rigidly to be cut down. Consequently, the scraper's effect on the landscape is opposite that of sandpaper. The softer areas spring back after the scraper has passed, leaving them higher than the denser area and producing a ribbed surface that can look like a neatly plowed cornfield at dusk. The correction is a quick follow-up sanding with a hard backup block.
Other trouble areas
surround the designed-in
features of a saya's
surface: slots, round
holes, intersecting edges
and the like. Scrapers
and sandpaper tend to
fall into slots and holes,
producing general
depressions around them
or, in the case of
scrapers, troughs
radiating out from them.
Only hard sanding
blocks can save you.
Inside junctions require
planning and perhaps a
specialized tool. If the
surfaces adjacent to the
seam have their grain
running parallel to the
crease, it's not hard to
sand smooth. But if the
grain of one or both
surfaces runs at an angle
to the seam, you may
have to be more
restrictive in the type of
care that you pay to that
surface.. The hidden
danger of working
around any problem area
is that it encourages
special attention,
resulting in a local
surface that's
inconsistent with the rest
of the object. |
Lacquer is a low-wetting
finish, which means it
does not noticeably
saturate the wood, but
lies on it as a film. The
surface tension of this
film will draw it away
from any sharp edge,
leaving little there and
making it easy to sand
through later when
leveling between coats.
Therefore, as part of
your pre-finishing
surface preparation,
soften, if not actually
round, all edges of the
work to be sure they will
remain adequately
coated. The slight
falling off of a surface as
it nears the end has
another advantage. It
compensates for the
tendency in leveling
between coats to do
extra work near the
edges which makes it
more likely you will sand
through the film there.
This relieving the surface
near the edge prevents
time- consuming spot
repairs later.
Once all surface irregularities have been removed and all the edges have been prepared, you can begin final sanding with fine papers backed by hard- felt or rubber sanding blocks. Hardwood blocks with coarse abrasive are good for dimensional leveling, but fine papers on hardwood blocks tend to glaze and will streak the surface with burnish marks. There's little value in finish- sanding beyond 320 grit. You will se some improvement of the surface past this point, but once lacquered the surface will return to what it looked like at 320 grit. Also, grits finer than 320 do little more than burnish the wood, making it more difficult for the lacquer to stick without blistering.
Step 2: Materials,
Equipment & Application - |
Shellac is gleaned from
the solidifying secretions
of insects that colony on
trees in Thailand and
India This material is
liquefied, refined and
broken into small pieces.
It is marketed as "orange
flake" or "French
shellac". You can also
obtain a bleached
shellac.
Lac is derived from the sap of the poisonous oriental tree, rhus vernicifera, and is refined several times to produce "flake lac", a glossy but brittle lacquer of varying degrees of purity. Both lac and shellac dry to a clear surface with a slight orange peel texture, and are soluble in denatured alcohol or turpentine. Varnish is a mixture of resin (copal, mastic, damar or sandarac) in a solvent. There are two types: oil varnishes, where the resin is melted with a drying oil and then thinned with a solvent; and spirit varnish, where the resin is dissolved directly in a solvent such as denatured alcohol or turpentine. These lacquers can be applied by brush, pad or spray, and in most cases the quality of the finished product will be the same. But because some of the materials used contain resins and oils that are dissolved by lacquer thinner, the finish can get muddy and the discoloration can get dragged around with a brush or pad. Otherwise, the steps in the finishing process are basically the same for brushing or spraying, the only differences being in the speed of application and the time involved in leveling the finish.
Essentially, lacquering
consists of three stages:
filling, leveling and
polishing. |
Throughout,
you should be inspecting
the surface for defects
and correcting them.
One chief concern of the novice is how many coats of lacquer should be applied. This consideration shouldn't be viewed in the same way as it is for painting: painting is accomplished when the surface is opaquely covered. Lacquering is not simply a covering job, for lacquer is not clear paint. On bad lacquer jobs you can actually see two surfaces, a thick layer of clear plastic and under that the surface of the base coat or wood. Done properly, however, you see one polished surface that emanates a uniform sense of depth. It is gotten that way not by the mere addition of clear stuff, but by a cyclic process of adding material and sanding it off until the surface being treated is truly flat, at least to the degree that the eye no longer distinguishes any texture. Only enough material must be left on the surface to enable you to polish it without breaking through to the base coat or wood. So the only answer to the question "How many coats?" must remain simply "Enough," that is, however many coats it takes to complete the job of leveling and polishing.
Effective application
technique is largely a
matter of speed and
consistency, graceful
motion and
thoroughness. You are
trying as quickly as
possible to coat a
surface evenly and
completely, with no
unblended areas. In
effect, you want to have
the entire object wet at
once. To do this, you
must move quickly from
surface to surface in a
preconceived patten that
will ensure
thoroughness, with
tightly spaced strokes
that overlap each other
and the objects edges. |
The process begins with
the application of a
sanding sealer diluted
with an equal amount of
lacquer thinner. Sanding
sealer is a kind of
lacquer specially
formulated to raise the
grain of the wood, to
provide a base for better
adhesion and to be easily
sandable. It gives you a
preview of the finished
surface, allowing you to
locate and repair any
imperfections.
After perhaps an hour's drying time a wood filler can be used on the open- pores of the wood. Most wood fillers consist of chalk, plus a touch of clay and pigment, carried in a mineral spirit or naphtha vehicle. The pigmented chalk is left in the pores of open- grained woods, where it fills most of the space. Thin the filler about 25% with naphtha and apply it with a rag, working the surface across the grain to clean off all excess filler. For woods with large-pores a second application may be necessary after three hours' drying time. Eight to twelve hours later, sand the surface clean with 320- grit paper to remove filler residue and raised grain. You will sand through the sealer coat in places, making an awful mess, but the next coat of sealer, applied just like the first, will blend perfectly.
The surface will now
appear improved but not
yet truly flat, and it will
take the remaining sealer
coats, applied heavily
but sanded almost
completely off, along
with the colored lacquer
base and subsequent
clear lacquer coats, to
complete the leveling
process. These will be
spread out over a period
of days, with no more
than four coats applied
per day. On the first day
I stay with the sealer,
applying three wet coats
one to two hours apart.
A wet coat means that
the solution is applied so
heavily that it |
floods the
surface, leveling itself to
a mirror gloss just one
taste short of drooling.
This welds the material
to the previous coat and
ensures adequate film
thickness. As the lacquer
coats build, a thoroughly
wet application is
necessary or a layered
structure will result,
which is prone to
blistering and ghosting.
Also, because of the low
solids contents of both
lac and shellac lacquers
you need the thick coat
just to have anything left
after the thinner has
evaporated. Straight
from the can, the solids
content is about 20%,
and when mixed with
equal amounts of thinner
it is 10%. Compared to
varnish, which is about
50% solids, this is like
mixing one quart of
varnish with one gallon
of thinner.
Perhaps the most important thing to understand about this low solids content is the fact that while the thinner is evaporating, the lacquer film is shrinking. Only one- tenth of what you spray will remain as a film on the wood. The rate of evaporation and shrinkage is extremely fast as first, so the surface can be touched within minutes of being drenched. But the evaporation rate decreases rapidly, and enough thinner is trapped with the film so that shrinkage is still perceptible after a week of drying. It is bad practice to apply more than three, at most four, coats of lacquer without allowing an overnight dry to let most of the trapped thinner escape. Otherwise, the thinner will be buried under so much lacquer that it may take weeks to evaporate completely.
After the first three coats
of sealer dry overnight,
sand the surface
thoroughly with 320-grit
paper on a block. This
dulls the shiny surface,
but the low spots will
still shine. The goal is a
uniformly |
matte surface
with no shiny spots, but
may sand through to the
wood in places. When
this happens apply more
sealer and sand again,
until there are no shiny
spots anywhere. Now
employ one las coat of
sealer to coat any wood
that has been sanded
bare, and begin applying
the colored lacquer base.
To color the lacquer base, use only japan paints or dry poster paint (flat opaque pigments in an oil-free varnish), toning it down with lampblack and burnt umber to suit whatever effect you are trying to achieve. Keep in mind that when varying pigments are mixed, if the tonal value is below medium, it will appear darker when dry; if above medium value, it will appear lighter. The lacquer is usually diluted with an equal volume of thinner, and it's applied at the same rate as the sealer, a coat every hour or two, no more than three coats per day. Let dry over-night and sand with 320- grip paper the next day. Repeat this cycle until you can level- sand the entire surface without sanding through to the wood anywhere or until you can no longer see any details of the underlying wood. Then apply the final three coats of clear lacquer and allow the surface to stabilize and harden for about five days, before final leveling and polishing.
Final sanding can be
done with 600-grit paper
wet. Use the paper with
a soft sanding block
behind it and with a
reciprocating, in-line
motion to prevent build-
up of lacquer dust on the
paper. The surface and
paper must be constantly
wiped clean, for this
white powder clogs the
paper and mars the
surface. When free of all
telltale shiny spots, wipe
the surface clean and
continue this abrasive |
action with the back side
of the wet paper.
Finally, with a fine abrasive polishing compound, such as Semichrome or Blue- magic, and a lamb's- wool or soft cotton pad, complete the polishing process. To avoid dirt scratching the surface, the compound should be applied to the pad, not to the surface. Use buffing compound sparingly and wet it frequently with water to create a slurry that helps to float the surface clean and keep the abrasive cutting. I usually buff in a circular pattern when using the fine abrasive compounds. When the surface has gained the desired luster, it is easiest to both clean and wax with regular furniture polish.
The quality of the
finished surface depends
completely upon the
success of each step,
from the preparation of
the wood to its final
polish. Critical
inspection will reveal
when a flaw is created.
Once you start
lacquering, it is too late
to repair the early stages,
but if you need to
relacquer once you've
begun polishing, first
wash the surface with
alcohol and water,
50/50, to remove
polishing residue and
wax. The surface may
be rebuffed at any time
in the future with the
fine compound to
restore its original luster. |