|
"THE STORY OF SHELLAC"
reprinted with permission from Zinsser Booklet by
the same name
In celebration of our 155th year manufacturing shellac, we have revised
this booklet, which was first published in 1913 and reprinted seventeen
times throughout the years. The purpose of this booklet is to share with
those who use and buy shellac the lore of shellac – its cultivation and
production – and to show how the unique properties of this natural resin
offer advantages still not duplicated by any single synthetic resin.
Shellac has an Ancient History
Shellac, as the word is commonly used, refers to all forms of
purified lac - a natural resin secreted by the tiny lac insect on certain
trees, principally in India
and Thailand.
“Lac” is derived from the Sanskrit word “lakh” which means 100,000 and
refers to the vast swarms of insect larvae that inundate lac trees during
brood season. There is a connection between the word “lac” and the
Indo-European word for salmon, “laks”, very likely a reference to great
numbers of the fish observed in spawning shoals.
Not much is known regarding the very early history of shellac. In the Vedic
period about 3,000 years ago it was called “Laksha.” One of the Vedic books
contains an account of a whole palace constructed entirely out of lac
resin.
Ancient Chinese and Indian civilizations used the dye extracted from lac for
dyeing silk and leather and as a cosmetic rouge and a coloring for head
ornaments. The superior adhesive quality of the resin made it useful for
setting jewels and sword hilts as well as repairing broken pottery. The
residue left after the extraction of the dye was made into a grinding wheel
for jade – a technique still in use today.
It was in the field of medicine, however, that the most extensive
applications for lac were discovered. It was prescribed either as an
emollient, or as a stimulant to tissue growth or in the treatment of gum
hemorrhages and menstrual disorders. In veterinary medicine lac was mixed
with lard and the paste used to fill the cavities in the hooves of horses
and cattle.
Europe
Discovers the Wonders of Shellac
Following the historical journey of Marco Polo to the Orient in the
late 13th century, shellac and its by-products began to make their way into
European commerce and industry. Accounts dating as far back as 1534
describe the cultivation, harvesting, processing and use of lac in
extraordinary detail.
By the mid-17th century shellac resin, shellac dye and shellac wax were
used with increasing frequency by painters not only to create their
masterpieces, but also to provide them with a protective finish.
Shellac became the preferred finish for craftsmen and artisans; it was the
coating of choice for fine furniture, woodcarvings, and turnings. To this
day some of the finest museum pieces still have their original shellac
finish.
The Golden Age of Shellac
Ironically, it wasn’t until the mid-19th century that shellac was
commonly used as a clear finish. Until that time it was processed mainly
for the dye that was extracted from the lac after it was harvested. This
rich, reddish-purple colorant was highly prized and much sought after by
the textile trade in both Europe and America
because it was an excellent substitute for Cochineal, a dye imported from
Spanish colonies in Mexico.
In 1856 an English chemist named Henry Perkin succeeded in synthesizing a
mauve-colored dye from an aniline derivative of coal tar. His discovery
forever changed the future course of the shellac industry. As the demand
for natural lac dye declined, the demand for shellac varnish began to
increase. Production plants began springing up throughout Europe, most
notably in Germany,
which soon developed a reputation for manufacturing the finest shellac in
the world. Efforts were also being concentrated on producing colorless
shellac. As far back as the 1830’s shellac chemists discovered that by chlorinating
an alkaline solution of shellac they could remove almost all of the color
and then precipitate the resin. The result was a pale, straw-colored
varnish that excelled any oil-base varnish for clarity.
1849: Shellac Comes to America
By the middle of the 19th century, Germany
was the center of shellac bleaching for all of Europe.
One such bleachery, located in the town of Mainz, employed a man named William
Zinsser as one of its bleaching foremen. Confident of his technological
skills and convinced that a good market for bleached shellac either existed
or could be created in the United States, Zinsser and his family emigrated
to America. Zinsser settled in New York City
in 1849 and built a home in Manhattan
on West 59th Street.
Almost immediately he set up a workshop in a building next to his home and
began to bleach small quantities of shellac that were sold to fellow
immigrants. From this humble beginning arose the first shellac bleachery in
the United States.
At that time Americans had never before seen bleached shellac, shellac
varnish, or so-called French varnish and therefore were unaware of the many
uses for this versatile, natural product. Initially, shellac sales were
confined to fellow immigrant artisans and craftsmen. As word of this marvelous
new varnish spread among tradesman of all nationalities the demand for
shellac grew from a few pounds per day to thousands of gallons by the turn
of the century; up to that point Zinsser shellac was sold to vendors who
packaged the product under their own label and name.
This practice ended in 1908 when Zinsser’s sons (shown standing on either
side of him in the photograph on the right) took over the company and began
to package their shellac under the Bulls Eye® label.
By the 1920’s there were several other shellac manufacturers in the U.S., including Bradshaw-Praeger, Haeuser,
Gillespie, Rogers
and Mantrose to name a few. Most of these companies either imported shellac
or prepared and packaged pre-mixed solutions of shellac and alcohol.
The next eighty years witnessed a veritable explosion in the commercial
applications for shellac. It was used extensively as a binder in the
manufacture of gramophone records from the turn of the century well into
the 1950’s, when manufacturers began using vinyl to press record albums.
Shellac was used to make shoe polish, felt sizing for men’s hats, hair
spray, floor wax, pharmaceutical, candy and fruit coatings; printing inks,
adhesives, grinding wheels, paper and foil coatings and electrical
insulators.
From the turn of the century through the 1950’s home builders and painting
contractors used shellac as a sealer for plaster walls and a fast-drying
varnish for interior woodwork, trim and floors. Today this beautiful
original finish can still be seen in many older homes.
The Rise of Lacquers and Polyurethane
The development of synthetic resin compounds early in the 20th century
together with advances in varnish formulation heralded the end of shellac’s
industrial and architectural dominance. Ironically, many of these newly developed
resins – such as Bakelite and similar phenolic-base compounds – were
created by researchers attempting to synthesize shellac.
Following World War I chemists discovered that nitrocellulose dissolved in
a powerful solvent mixture produced a crystal clear coating that dried as
fast as shellac, thus giving rise to the widespread use of lacquer as a
furniture finish. After World War II alkyd varnishes were developed and by
the 1950’s the public was introduced to the first oil-base polyurethanes. As
these finishes displaced shellac as the standard finish coating for
interior woodwork and floors, one-by-one America’s shellac manufacturers
either closed their doors or merged with others.
From the 1960’s until the early 1990’s shellac seemed forgotten by everyone
except those who manufactured it and the contractors, hobbyists, and
knowledgeable devotees who used it. All of the largest makers of shellac
were out of business or existed as subsidiaries of the one remaining
manufacturer: William Zinsser & Co.
How Insects Make Shellac
Shellac has the distinction of being the only known commercial resin
of animal origin. It is produced by a tiny red insect (Laccifer lacca)
which, in its larval stage, is about the size of an apple seed. Swarms of
the insects feed on certain host trees, commonly called "lac
trees," in India
and Thailand,
the main lac-producing countries.
Their whole life cycle spans six months and is devoted to eating,
propagating and creating lac as a protective cocoon for their larvae.
During certain seasons of the year, these tiny red insects swarm in such
great numbers that the trees at times take on a red or pinkish color. When
settled on the twigs and branches, they project a stinger-like proboscis to
penetrate the bark.
Sucking the sap, they begin absorbing it until they die. In shellac lore
this is the 'feast of death." While they eat they propagate, with each
female producing about one thousand eggs before dying.
In the body of the lac insect the digested tree sap undergoes a chemical transformation
and is eventually secreted through pores. On contact with the air, it forms
a hard shell-like covering over the entire swarm. In time this covering
becomes a composite crust for the twig and insects. Only about five percent
of the insects amassed on the trees are males. The female is the main
shellac producer.
While she is secreting lac, she is preparing herself to die after providing
a fluid in which her eggs will mature and from which the future supply of
bugs will come, to repeat the process of swarming, propagating and creating
the next season's shellac harvest.
The males, having fertilized the hordes of females, also begin their
life-ending feast. Although they contribute relatively little more to the
shellac crop, they have already assured an ample supply because the females
vastly increase their output of lac after being fertilized. The great mass
of male and female bugs on each tree gradually becomes inactive as the
shell-like covering forms over them. In the sixth or seventh months, the
young begin to break through the crust and swarm to new feeding grounds.
Shellac cultivation yields a large crop by helping the larvae find better
locations for their feast. This involves simply cutting lac-bearing twigs
from an infested tree a few days before the emergence of the larvae. A
bundle of such twigs, known as 'broodlac," is tied to an un-infested
tree on which there are many tender new shoots. This results in a higher
survival rate of insects and a greater yield of lac since only a little broodlac
gives forth sufficient larvae to infest a tree thoroughly. No further
attention is needed until shellac is harvested.
How Lac Is Harvested
Shortly after the young have swarmed at the end of the adults' life
cycle, natives begin to harvest the lac encrustation from the trees. Only
one crop is taken per tree. Young are hatched, however, twice a year.
Natives gather millions of encrusted twigs, called "sticklac,"
for transport to simple factories or refining centers where the lac crust
is scraped off and processed. The resin is also collected in the forest or
orchard by smacking the branches with a wooden mallet. This material is
called "grainlac." In either case, this is the first step in the
harvest of shellac resin.
At refining centers, sticklac is scraped to remove the resin from the twigs
and then it is ground (as is grainlac), usually in a primitive,
hand-cranked mill. At this stage, the ground lac contains a mixture of
resin, insect remains, twigs and other impurities. This is now passed
through a coarse screen to remove the larger size twigs. After the lac is
ground and the chaff sifted out, it is soaked in water for several hours in
large cup-shaped jars. These are about two feet high and have rough
serrated inner surfaces.
A ghasandar jumps into the jar and rubs the lac with his feet against the
rough surfaces. This action causes the lac seeds to break open, releasing
dye and insect remains. The ground lac is rinsed to remove the dye and then
spread out on a concrete floor to dry in the sun. The dried resin is called
"seedlac" because of its grain-like appearance and ranges in
color from pale lemon to dark red.
Commercial shellac falls into three categories that reflect the processes
used in their manufacture: hand-made, machine-made and bleached.
Hand-Made Shellac
This process involves a primitive method still used by small local
factories to produce flake shellac. Generally, three workers carry out the
process from start to finish. They begin by packing seedlac into a long
round bag about the shape of a section of two-inch fire hose. These bags
vary from 25 to 40 feet in length. Small sections of the long bag are
heated uniformly by slowly rotating them over a charcoal fire in an oven
called a bhatta. While a helper twists the far end of the bag, the
operator, called a karigar, holds the hot end of the bag and squeezes the
molten lac through the pores of the bag. The helper at the far end
continues to pinch the bag by twisting it, forcing more lac toward the
karigar.
The karigar lets the oozing shellac fall on the hearth stone, which has
been moistened with water, and scrapes the surface of the bag periodically
with a spatula. To prepare for the next step, he repeatedly picks up lac
from the hearth-stone with an iron spatula and puts it on the rotating bag,
basting it back and forth to get a viscous, uniform melt.
This soft lac is then turned over to a bhilwaya, who works it into thin
sheets. With a strip of palm leaf, he spreads the molten lac over a ceramic
jar filled with hot water, and then pulls off a piece about two feet square
and a quarter inch thick.
Standing before the fire with the sheet, the bhilwaya manipulates it to
soften it uniformly. At that point he uses his hands, feet and teeth to
stretch it into a paper-thin sheet about 5 feet by 4 feet. This is laid
aside to cool and harden, after which it is broken into flakes.
If there is a demand for it, the bhilwaya will opt instead to make button
lac. Instead of stretching the molten lac into sheets, the bhilwaya takes
the lac from the twisting bag with a spatula and spreads it out in the form
of a circular disk or button about one to three inches in diameter. Before
it hardens completely the button is stamped with the seal of the
manufacturer.
Machine-Made Shellac
Shellac manufactured by modern mechanical methods is called
machine-made shellac, mainly to distinguish it from shellac made by the
indigenous – and, frankly, more fascinating – hand technique. There are two
processes - one based on melting (heat process) and the other on solvent
extraction.
In the heat process, seedlac is melted on steam-heated grids. The molten
lac is forced by hydraulic pressure through a fine wire screen. The
filtered shellac, still molten, is collected and transferred to a
steam-heated kettle from which it is dropped onto rollers. It is squeezed
out on the rollers, coming off as a thin sheet to be broken into flakes.
The thickness of the flake is controlled by adjusting the roller pressure.
All flake shellac produced by this process contains wax.
The solvent process produces three types of
shellac:
1. For the wax-containing grade, raw seedlac and alcohol solvent are
charged into a dissolving tank. The solution is refluxed for an hour or so
and then filtered to remove insolubles. The filtered shellac is fed to a
series of evaporators where it is concentrated into a viscous melt, which
is then dropped onto rollers that sheet it out for removal in flake form.
Darker, wax-containing flake shellacs such as Garnet are made this way.
2. Dewaxed shellacs are made by dissolving seedlac in either cooled alcohol
of a very high proof or heated alcohol of a lower proof. The resulting
solution is then passed through a filter press to remove the wax, after
which the filtered shellac is then concentrated in evaporator tanks. The
viscous shellac is then rendered into flakes. Dewaxed Lemon and Dewaxed
Garnet shellacs are manufactured using this process.
3. Dewaxed/Decolorized shellacs are made by the same process as dewaxed
grade, except that after dewaxing the solutions are forced through
activated carbon filters to remove the darker coloring constituents from
the shellac. By varying the amount of carbon, contact time and quality of
the seedlac, one can obtain grades of shellac ranging in color from light
amber to extremely pale straw. Examples of these shellacs include Blonde,
Super Blonde and Ultra Blonde.
Bleached Shellac
Although most of the bright red lac dye can be removed with activated
carbon, some shade of red-orange remains. For many applications, however, a
nearly colorless film is preferred. Kusmi shellac, while extremely light in
color, is very expensive and not available in commercial-scale quantities.
The development of shellac bleaching in the early 19th century solved this
problem with a relatively inexpensive process that could produce enormous
quantities of very pale-colored shellac.
Since establishing the first U.S. shellac bleachery in 1849,
Zinsser has made significant advances in bleaching tech-nology. Today our
MBZ division bleaches seedlac in its Attleboro,
MA facility. From this
bleached resin we make Bulls Eye Clear Shellac and B-I-N®, our
white-pigmented stain killing primer.
The bleaching process involves dissolving seedlac, which is alkali-soluble,
in an aqueous solution of sodium carbonate. The solution is then
centrifuged or passed through a fine screen to remove insoluble material.
The next step is bleaching the cooled solution with dilute sodium
hypochlorite to the desired light color. The shellac is then precipitated
from solution by the addition of dilute sulphuric acid, filtered off,
washed with water, ground and dried in vacuum driers.
The final product has a granular consistency and is dissolved in alcohol to
give a milky, creamed-honey colored solution. Both Clear and Amber Bulls
Eye Shellac contain from 3% to 5% natural shellac wax, which gives them
their somewhat milky appearance in the container but does not affect the
clarity of the dry film.
While more efficient equipment and machinery have replaced much of the work
that was done by hand in the 19th and early 20th centuries, the bleaching
process itself has not fundamentally changed in over 100 years.
What Does the Term “Pound Cut” Mean?
Bulls Eye Shellac is manufactured in a 3-lb. cut. "Pound cut" is
a term unique to the shellac industry. It refers to the number of pounds of
shellac dissolved in one gallon of alcohol. A 3-lb. cut contains
approximately 29% shellac; a 2-lb. cut contains about 21% shellac.
As a rule the following pound cuts are used:
1-lb. – Pre-stain sealing, French Polish finishing
2-lb. – Pre-finish sealing; general wood finishing
3-lb. – Floor finishing; sealing knots & sap streaks
4-lb. – Sealing tough knots & sap streaks, stains*
* The 4-lb. cut is generally used by professionals
Does Shellac Have a Shelf Life?
Freshly made shellac dries very quickly to a hard, durable and
water-resistant finish. However, because it is a natural material, shellac
is also perishable and after six months an ordinary solution of shellac and
alcohol begins to undergo a chemical change: it gradually takes longer to
dry; the dried film is softer and more prone to scratches and water damage.
This change is even more pronounced for bleached shellac. After 18 months
it may take hours to dry or not even dry at all and is considered to have
expired. Exposure to heat also accelerates the expiration process.
Zinsser research chemists have succeeded in prolonging the shelf life of
shellac in two ways: the first involves a specially formulated solution;
the second involves a patented process (U.S. Patent No. 6,348,217 issued 19
February 2002) for the production of the resin itself.
Bulls Eye Shellac is the only pre-mixed shellac in the world guaranteed to
dry quickly to a hard, durable, finish for 3 years after the date of
manufacture. However, since storage conditions can greatly affect the shelf
life of our shellac always check the manufacturing date to find the
freshest Bulls Eye Shellac and apply some of the product to a test surface
to check the dry time and film hardness.
To ensure the long life of Bulls Eye Shellac keep the container tightly
closed and store in a cool, dry place where the temperature does not exceed
75o F. Extreme heat can ruin shellac in less than a week. There is no need
to worry about cold weather: since shellac is alcohol-based it is
unaffected by freezing temperatures.
Common Shellac Myths
Myth: Shellac is made from bugs or bug droppings.
FACT: Shellac is a resin secreted by the lac insect to form a cocoon, much
like a silk worm. It takes about 100,000 lac bugs to make 1 lb. of shellac
resin.
Myth: A shellac finish turns white when water touches it.
FACT: Fresh shellac is remarkably water-resistant and, in most cases, will
stay clear after hours of exposure to water, making it a great finish for
most interior surfaces, including woodwork, trim, doors, cabinets,
paneling, floors (yes, floors!) and furniture.
Myth: Shellac scratches easily and is very brittle.
FACT: Shellac is a durable finish that is much less brittle than lacquer
and does not scratch as easily. Unlike polyurethane, a damaged shellac
finish can be easily touched up or renewed by applying another coat.
Myth: Shellac is incompatible with other finishes.
FACT: Shellac will adhere tenaciously when applied over almost any other
type of finish. When used as a sealer under certain polyurethanes, however,
regular shellac may not be compatible because it contains a small amount of
natural wax. To seal wood before applying polyurethane and other finishes
we developed Bulls Eye® SealCoat,™ a shellac-base universal sealer that is
100% wax-free.
Myth: Shellac turns an ugly dark color as it ages.
FACT: Shellac is UV-resistant and does not yellow or darken with age. The
dark shellac that people see in older homes is a less-refined version of
shellac that either was naturally dark or was tinted by contractors when
dark wood colors were preferred in the early 20th century.
Myth: Shellac is an old-fashioned, outdated finish.
FACT: Shellac has more modern features and benefits than any other wood
finish in the world.
Shellac's Great Properties
Shellac has such remarkable properties that if it were just recently
discovered it would be hailed as a miracle finish of the 21st century.
* All-natural – Shellac is an all-natural resin of insect origin that is
harvested regularly and is therefore a renewable resource.
* Fleeting alcohol odor – Shellac is dissolved in denatured ethyl alcohol.
It has a fleeting, antiseptic odor that dissipates quickly as the product
dries.
* Easy to use – Shellac is user-friendly and virtually goof-proof. It can
be applied with a brush, pad, sprayer, or wiping cloth.
* Super-fast dry time – Shellac dries to the touch in MINUTES and, in most
cases, can be sanded or recoated in a little over half an hour.
* Cold temperature application – Unlike other finishes shellac can be
applied in cold temperatures (40o F. and below) without concern over proper
drying and curing.
* Non-toxic/hypoallergenic – The U.S. Food & Drug Administration has
certified shellac as a protective glaze for candy and pharmaceuticals.
* Non-yellowing/non-darkening – Shellac is UV resistant and will not yellow
or darken with age – unlike oil-base finishes.
* Enhances the beauty of wood grain – Shellac brings out the rich warmth of
wood grain. Finished surfaces look soft and natural, not plastic-coated.
* Sticks to glossy surfaces and finishes – Shellac is prized by everyone
who uses it for its incredible adhesion. It will stick to just about
anything.
* Dried film is impervious to odors – Two or more coats of shellac will
seal in any kind of odor in any type of porous surface.
* Stain sealer – Shellac is arguably the world’s most effective stain and
knot sealer (another reason why we use it to make B-I-N® Primer-Sealer).
* Easy to touch up and recoat – Unlike other finishes shellac can be easily
touched up if it is scratched or worn; a new coat of shellac melts itself
into the existing coat.
* Easy to clean up or remove – Shellac is dissolved by household ammonia as
well as alcohol, making it very easy to clean brushes and other tools.
Best of all, a shellac finish looks great. Bulls Eye® Shellac in liquid and
aerosol form is still the craftsman’s choice as a finish for woodwork and
as a protective sealer for countless uses. On the Internet you can find out
more about shellac and how it is used at: Zinsser
Finish Company.
c/o Ken Johnson
Marietta, Georgia
email
to [kej at jprconsulting.com]
|
