"Furniture Finishing Textbook" by W. E. Martin: The Importance of Finishing (Chapter One)

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FURNITURE FINISHING TEXTBOOK
CHAPTER ONE: The Importance of Finishing
by W. E. Martin


In the style-conscious furniture business, good finishing is perhaps
the most critical factor. The sale of furniture is highly influenced
by its decorative value and its eye appeal (Even in lower priced lines
there is ever-increasing demand for excellence of these values.)

Good design is of course essential, but many factors of appearance,
color, sheen, depth, wood value are determined in finishing. Even the
lines and decorative elements of design are intensified or subdued by
color distribution or density achieved in finishing. For these reasons
the finishing operation has been and likely will continue to be a
major concern in furniture production management.

The evidence of this concern is seen in many new or modernized
finishing departments, carefully engineered and provided with the best
available equipment for handling, application, and drying. These
improvements do permit much better control of the finishing operation.
But furniture finishing cannot be automated for virtual push-button
control, as is the case with many metal finishing operations. It is
inherently more complex and demanding, and has far more variables to
contend with. There are more frequent changes in styling. When new
groupings are planned, sample pieces are carefully finished to meet
the approval of the designer, the stylist, even perhaps of important
buyers. While production requirements are kept in mind at this point,
or should be, the effort of course is to produce outstanding
appearance values. When actual production is started, these values
must be duplicated or closely approximated in volume operation, and
within reasonable time and cost limits. These require a high degree of
knowledge and experience on the part of supervisors and operators;
without it there are constant troubles and inferior results. It is a
tribute to the competence of finishing superintendents and their crews
that most finishing departments do run quite smoothly and turn out
high-quality finishes. But there seems always to be a shortage of
experienced supervisors; those who presently handle these assignments
are constantly on the lookout for more and better information on
finishing.

The articles in this series were written to assist in meeting this
demand. Obviously, no one can become an experienced finisher by
reading. It takes training and practice; for industrial finishing it
further takes practice under factory conditions. But many problems and
troubles arise from failure to understand basic principles. These
articles are based on material used in finishing training schools.
These were short intensive courses designed to give finisher
candidates a basic understanding of furniture finishing-its
controlling requirements and objectives, the materials and techniques
used to attain them, the problems encountered. While the main purpose
of this work is to supply information that may be useful to those
engaged in finishing, we hope it may also serve to give others
interested in the manufacture and sale of furniture a better
understanding of the art of finishing.

We stated above that furniture finishing is inherently complex and
demanding. This is true for two broad reasons. The first is that we
are working with wood, which is a highly variable material. It varies
widely in color and structure between species and even in separate
parts of the same tree. While the effects of this variation can be
subdued by carefully selecting and matching wood, factors of waste and
cost impose definite limits to this procedure in furniture production.
In many cases, different types of wood are used in the same piece for
good reasons of structural quality as well as cost.

Wood contains natural dyes or colorants which are not evenly
distributed, and thus produce color variation in different areas of
the surface. If this variation is related to the figure, we may wish
to preserve or intensify the difference. If in unrelated streaks, as
between heart wood and sap wood, we usually need to equalize the
color. Wood is porous and thus absorbs; it takes on or gives off water
rapidly with changes in atmospheric moisture. It is fibrous in nature-
the individual fibers are prone to sweII and raise on the surface when
moisture is absorbed, thus affecting the performance of stains and
other finishing materials. Add these factors together and you have a
variable and changeable surface over which to achieve a rather
exacting artistic result.

The second broad reason for complexity in furniture finishing is
inherent in the requirements of finish styling. The primary objective
of finishing is to add beauty and artistic merit. We must develop all
the possible value and beauty inherent in the natural wood, and we
must accent or complement features of design. We are involved with
factors of color distribution and color depth, clarity, sheen, etc. To
get the required values we must use a somewhat complex color system
employing a variety of colorant and film forming materials, each one
affecting the final color and each one critical in the amount and
technique of application. We must often produce overall color values
that are relatively light and delicate, therefore more difficult to
control than the strong, dark colors. We must have consistency in
overall color from piece to piece, yet with each piece treated in such
a way as to bring out the maximum value of its particular design and
of the wood figure that occurs throughout it. New finishes are
continually being introduced and frequently several different
finishes, probably on several woods, will be running in the finishing
room concurrently or in rapid succession on a great variety of shapes.
All this means that personal judgement and skill are constantly
involved, adjusting to and compensating for variations in wood and
shape.

Along with artistic merit, the finish must have protective value and
good durability. It should prevent excessive absorption of atmospheric
moisture which would cause swelling and warping of the wood. It should
resist surface soiling and staining. It must be resistant to checking,
to damage by accidental spillage of various household materials, to
mars and scratches, and to drastic color change with age or light
exposure: Unless the finish has reasonable durability, the original
beauty so carefully developed through finishing will not last.

Obviously, not all finishes are complex or difficult. It is possible
to give wood sufficient protection for the average conditions of
interior service with a very simple finish, and in fact, good
toughness and durability is sometimes easier to obtain in the simple
system. If all that is needed is a coating of lacquer or varnish on
the natural wood, or a white paint job using undercoat and enamel,
finishing is no great problem. If we are putting a printed grain on
plywood using ground coat and graining ink with sealer and topcoat,
finishing can be pretty much automatic. The thing that makes wood
finishing complex, the controlling reason for the considerable number
of operations and materials involved in many systems is the demand for
artistic values. Furniture manufacturers spend from 5% to 10% or more
of the total factory selling price on the finishing operation. The
simplest type of finish with satisfactory protection and durability
could be obtained for less than 5%. Everything beyond that is for the
sake of improving the beauty and sales appeal.

The first requirement for successful finishing is to understand and
face up to the problems involved. The individual operators must be
properly trained. There must be careful organization. There must be
constant inspection and control at every stage of the finishing
operation.


THE FINISHING SYSTEM

The beauty of finish that we see in a well-done piece of furniture is
produced by a sequence of operations involving a number of separate
and distinct materials. Some of these operations have to do with
producing desired color values, including distribution of color. Some
are done to correct undesirable variations in the wood, some to accent
wood values. Some operations are for leveling and smoothing the
surface. Some are for building depth and fullness of finish, and some
are for producing a surface sheen and clarity which is pleasing and
appealing to the eye.

The finishing system in one case may be quite simple, involving only
three or four operations. In another case, it may be elaborate,
requiring a dozen or more operations. It depends in part on the wood
and in part on the final values required. Whatever the number of
operations included, they tend to follow a certain sequence. As a good
approach to the general understanding of wood finishing, we will start
by outlining a complete finishing system, including all the operations
that might be used, listing them in the normal sequence, and
describing the purpose of each.

We will deal first with the clear transparent finishes as distinct
from painted opaque finishes. The complete system may include any or
all of the following operations:


1. Bleaching

Many of the preferred wood finishes require a very light undertone or
background color. To get this value on colored woods such as walnut or
mahogany, and retain full transparency, it is necessary first to
remove or subdue the natural wood colorant We do this by bleaching,
either partially or completely, as may be necessary to permit
subsequent staining to the desired background color. Bleaching also
helps to subdue unwanted color variation in the natural wood; it is
sometimes done primarily for this purpose.

We can lighten the wood background in another way by applying a
translucent coating of white or light pigmented material, usually a
pigment toner. This method was formerly used quite extensively but is
now usually avoided because it sacrifices transparency. It is
occasionally used very sparingly as a supplementary operation to
subdue dark streaks remaining in the surface after bleaching. If
pigment toner is used overall, it will be used at the body staining
operation, Number 4, below.



2. Pre-Staining or Uniforming The Wood Color

For many finishes, we can start with the natural wood color, but there
may be in our piece some undesirable color variations-for example,
some lighter sap wood areas; or the piece may be built with different
woods, such as a white gum frame with mahogany or walnut veneer in the
drawer fronts. For this situation, We must first "equalize" by shading
as required on the lighter areas. Otherwise, they would come out
lighter in the final finish. This operation is generally called sap
staining or prestaining.



3. Figure Accent Shading

In production finishing, this operation is usually combined with
operations Number 9 or Number 11 as described below, but for finest
natural effect may be done at this point. The purpose is to accent
wood figure by introducing light and dark contrast. We do this by
shading in color over the lines of figure. We can get still more
contrast by also sanding out color in adjacent areas after body
staining, as described in operation Number 5.



4. Body Staining

After these preliminary operations, the next step is usually to apply
a uniform overall application of the desired undertone color . We will
use for this purpose one of the stains described in Chapter 3 (WOOD
STAINS AND TONERS), the choice depending on the values we want to
achieve.



5. Strike-Out

As noted in Number 3 above, we can also emphasize wood figure by
sanding out undertone color along the borders of the lines of figure.
For dark undertones this is most effective if done at this point after
staining and before washcoating. For light undertone finishes, it is
more effective if done after filling, and may be repeated in the glaze
wiping operations.



6. Penetrating Sealer

This operation is added when it is desired to produce the "down-in"
appearance of an oiled finish. The material used is a treated oil or
thin varnish. To produce good value it must strike in and penetrate
the wood, therefore must be used before washcoating or any other
surface sealing coater, such as Pigment Toner. It is usually applied
after body staining with NGR stain, and followed by washcoating before
filling. If filler is not required, it is followed by sealer, Number
10.



7. Washcoating

If a filler is to be used, it is usually necessary to control the
staining action of the filler, which comes next. The colored filler,
which is applied overall and wiped off, will have an overall staining
value, and we usually want to minimize this staining action on the
area between pores. We do this by applying over the stain before
filling a "washcoat" sealer. This is a very thin coating, which leaves
the pore open, but seals the area between, therefore causing the
filler to wipe away more cleanly. In some finishes this washcoat
sealer is tinted, the general idea being that this adds depth to the
undertone color. A properly selected washcoat sealer also adds
materially to the toughness and adhesion of the complete finish.



8. Filling

In the case of the large pore woods, we need a filler. The purpose is
not only to fill the pore, but also to color the pore, usually in
contrast with the undertone color. The preceding washcoat application
helps to obtain this desired contrast. It should be noted that some
finishes on walnut and mahogany are intentionally done without filler
to produce an open pore effect; or the filler is highly reduced to
produce a partial filling action.



9. Shading On Filler

Most well styled finishes require a shading in of color for desired
contrast at borders or contours, and this is also done to accent wood
figure. Figure shading may be done at operation Number 3, but in
production finishing it is more commonly combined with contour
shading, either after filling or after sealing. Some finishers prefer
to do these operations on the fillers so they will be softened or
merged by the subsequent sealer coat. More commonly it is preferred to
do them after sealing when it is easier to see and control the result.
As mentioned under Number 5, for light background finishes, figure
accenting by sanding out color (strike-out) is most effective if done
at this point after filling.


10. Sealing

After filling and any additional color operations on the filler, the
next step in most finishes is a coat of "transparent sealer", either
clear or tinted for additional color depth. This seals off the surface
and provides a smooth foundation for subsequent overtone color
treatments and for topcoats. The sealer is normally sanded to a smooth
surface.



11. Shading or Padding On Sealer

If not previously done on the filler, "gun shading" is usually done at
this point for intentional contrast or for correction of unwanted
colao variation. Hand color padding for accenting wood figure may also
be done here, but is often done after the first topcoat.



12. Glazing

This operation is included in nearly all better finishes. It consists
of a very thin application of translucent pigment color in a wiping
vehicle. It is applied overall and wiped clean, or in some cases it is
wiped or brush blended to a desired distribution of overtone color.
Glazing color remains in low spots of carvings or edge molding, thus
accentuates these features. We can also further emphasize wood figure
by wiping out glaze (or by sanding out after drying) over the lighter
areas produced by strike-out in previous operations. Overall, glazing
adds an effect of color depth. By contrast, unglazed finishes have a
"raw" look.


13. Spatter

These additional color operations may be done almost anywhere in the
finishing system. Distressing is occasionally done on the wood or
after the undertone stain. Spattering is more commonly done on the
sealer coat or after the first coat of lacquer. The purpose of these
operations is to produce an antique effect.



14. Topcoat

When all coloring operations are completed, the piece is given one or
more transparent topcoats.


15. Rubbing


When the finish is completely dry, it is rubbed to the desired sheen.



VARIATIONS FOR SMALL PORE WOODS

For cherry, maple or birch, which do not require filling, Number 7 and
8 operations are normally omitted. However, if it is desired to
develop or intensify the pore pattern, we may use instead of a filler
a thin pigment wiping stain (or glaze), or a penetrating sealer
containing pigment color. This is generally applied directly over the
body stain without washcoating, and wiped clean. Otherwise the system
may include any or all of the above operations.



PAINTED FINISHES

The better painted finishes also involve a system of several materials
and operations. They usually start with a pigmented sanding undercoat,
followed by a second application of opaque pigmented material, such as
lacquer enamel, in the desired undertone color. (The sanding undercoat
may be tinted and used for both coats.) Over this foundation there
will usually be added sealer and glazing, plus striping, decoration,
spattering, and distressing as desired. Variations include
brushmarking of the base color coat, textured base coats for a pebble
effect, strike-out (or wipe-out) of base color to show streaks of wood
underneath-all for desired antique effect. The system is usually
completed with a low-sheen clear topcoat which is not rubbed.