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I thought I knew about shellac......

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  • I thought I knew about shellac......

    This is long but very informative

    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.

    For three thousand years, lac has provided the natives of India with purple-red colours for dyeing their clothing and a material they used to fashion ornaments and trinkets. It was prized as a decorative lacquer as far back as the sixteenth century.

    Aniline and other chemical dyes have long replaced lac-derived dyes. But despite the many synthetic resins produced by the chemical industry, natural shellac still retains its important place in the decorating products field as well as in such diverse applications as pharmaceutical, candy and fruit coatings, printing inks, furniture finishing, adhesives, grinding wheels, hat stiffening, and paper and foil coatings.

    Following is some information for those of you who use and buy shellac, who want to know the lore of shellac, its cultivation and production, and to show you how the unique properties of this natural resin can offer advantages still not duplicated by any single synthetic resin.

    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 (Lac Laccifer) which in its larval stage, is about the size of an apple seed. Swarms of these insects feed on certain host trees, commonly called "lac trees," in India and Thailand, the main lac-producing countries. Their life cycle of about six months is devoted to eating, propagating and making lac as a protective shell 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 colour. 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 literally feed themselves to death. In shellac lore this is the "feast of death." At the same time propagation continues, with each female producing about one thousand eggs before dying.

    The female is the main shellac producer. She provides the fluid in which her eggs will mature and hatch. This fluid is actally the lac which undergoes a chemical transformation in the females body and is eventually exuded. On contact with the air, it forms a hard shell-like covering over the entire swarm. In time this covering becomes a composite crust of twigs and insects.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 month, the young begin to break through the crust and swarm to new feeding grounds.

    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 from a single tree, however the young are hatched twice a year.

    Natives gather millions of these encrusted twigs for transport to simple factories or refining centres. Here the encrustations are scraped to remove the resins, it is then ground and passed through a course screen to remove the twigs and chaff. It is then soaked in a large jar of water for several hours. Afterwards a stomper jumps into the jar and rubs the lac with his feet against the rough surfaces. The object is to break open the lac seeds so the dye will flow out and the insect remains will be freed from the resin. Dye, water and scum are removed with several rinsings. The ground lac is spread out on a concrete floor to dry in the sun.

    The semi-refined product from this operation is known as "seedlac" from its grain-like appearance. It is yellow to reddish-brown in colour, depending on the type of tree and the location from which it came. This is the raw material from which both orange flake shellac and bleached shellac are made.

    The shellacs of commerce fall into three categories which 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 native factories to produce orange shellac. 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. 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 keeps pinching the bag by the twisting action, forcing more lac toward the karigar.

    The karigar allows the oozing shellac to fall on the hearthstone, which has been wet with water. He repeatedly picks up lac from the hearthstone with an iron implement and puts it on the rotating bag, basting it back and forth to get a viscous uniform melt.

    This soft lac is turned over to a "bhilwaya," who, like a taffy puller, works it into sheets. With a strip of palm leaf, he spreads the molten lac over a ceramic jar containing hot water, and then pulls off a short sheet about two feet square and 1/4 inch thick. Standing before the fire with the sheet, he manipulates it to soften it uniformly, then starts to stretch it using hands, feet and teeth. He ends up with a very thin sheet about 5 feet by 4 feet. This is laid aside to cool and harden, after which it is broken into thin flakes.

    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 more colourful - hand process. There are two processes - one based on melting (heat process), the other on solvent extraction (solvent process).

    In the heat process, seedlac is melted on steam-heated grids. The molten lac is forced by hydraulic pressure through a filter cloth or fine wire screen. The filtered shellac, still molten, is collected and transferred to a steam-heated kettle from which it is dropped onto rollers. where it is made into a thin sheet to be broken into flakes. The thickness of the flake is controlled by adjusting roller pressure.

    In the solvent process, raw seedlac and solvent, usually ethyl alcohol, are charged into a dissolving tank. The solution is refluxed for an hour or so and then filtered to remove insolubles. The filtrate is then placed into a series of evaporators where it is concentrated into a viscous melt. The melt is then dropped onto rollerswhere it also is made into thin sheets and then broken up into a flake form.

    Bleached Shellac

    Even though most of the bright red lac dye is removed when sticklac is washed, some of the orange color persists. When dissolved in alcohol, orange shellac forms an amber-coloured solution and the dried film has a distinctive amber cast. For many applications, however, a colourless film is preferred. To meet this market preference, the colour is removed by a bleaching process.

    The 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 lac along with any dirt and other insoluble material. The next step is to bleach the solution with dilute sodium hypochlorite until the desired lighter colour is reached. 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 is a while powder commonly referred to as bone dry shellac, which dissolves in alcohol to give a milky white solution. The opaqueness is caused by the natural wax content of shellac which settles out on standing, leaving a clear solution on the top. The wax is easily redispersed and should be stirred back into suspension before use. Solutions of bleached shellac have traditionally been called "white shellac" to distinguish them from orange shellac solutions. This is somewhat of a misnomer because they both dry to a clear, colourless film.

    Shellac's Great Properties

    Shellac, as a resin with such a remarkable combination of properties that if it were a new synthetic material, it would be hailed as a wonder product of modern chemistry.

    Probably its solubility in alcohol at a time when alcohol was one of the few available solvents led to the discovery of its value as a finish for early furniture, musical instruments and other wooden objects. It is as actually an ethyl alcohol solution that it is used today as a finish and sealer. This Alcohol solubility has two big advantages: shellac solutions dry quickly - in about 45 minutes, at any temperature and there is no objectionable paint smell, only the familiar fleeting odour of alcohol.

    Shellac is also alkali-soluble. This is important in bleaching and with some industrial uses. It also allows the wood finisher to clean up his shellac brushes in a solution of household ammonia and water. It is as modern and easy as cleaning latex paint in soap and water.

    Shellac is unmatched in its adhesion to just about any material that needs finishing or painting. Shellac will adhere firmly to such hard-to-stick-to surfaces as glossy paint, metals, ceramic tile, glass or plastics.

    Shellac has wide compatibility. Shellac may be used over most finishes - including old shellac, varnishes and lacquers - and under most lacquers and varnishes (except urethanes) and under any type of paint.

    Shellac forms a continuous film that is impermeable to the most hard-to-contain stains. It seals off bleeding knots and sappy streaks in new wood that are the bane of painters. With shellac, there's no popping through a finish coat of paint to spoil the job. It works equally well on stains of all kinds - stains from water leaks, grease marks, marking pens, graffiti, crayon, smoke and soot from fires. Not only does it seal off fire damage so the premises can be painted, but it also seals off the smell of smoke as well.

    Shellac is non-toxic and so has been FDA-approved for use to coat candy, pharmaceuticals and fruit. Because it is non-toxic, it is absolutely safe to use on children's toys and furniture.

    A shellac finish is easy to maintain. Worn spots, scratches or marred areas can be touched up easily by shellac liquid being brushed on or sprayed from a handy aerosol can. The new shellac will blend in well with the old.

    Best of all, a shellac finish also looks great. Shellac imparts a clear hard film with a high gloss that can be buffed to a glowing velvety sheen. No wonder it's still the craftsman's finish of choice.

    Shellac's 1001 Uses

    To say that shellac has 1001 uses may sound like an exaggeration. I doubt that anyone has counted all of them. For most applications, a 3-lb. cut is recommended. The 4-lb. cut which is a heavier concentration, is sometimes preferred for sealing persistent stains and knots, but it is usually bought by professionals who cut it with alcohol prior to use.

    POUND CUT (3-lb. cut, 4-lb. cut, etc.), a term unique to the shellac industry, refers to a manufacturing formula. It specifies the number of pounds of shellac dissolved in one gallon of alcohol. Over the years, it has been used to express the solids content or "strength" of shellac solutions. The ready-to-use 3-lb. cut, for example, is about 29% shellac; a 4-lb. cut, 35%. For some uses, as in French Polishing which is discussed later, shellac is thinned to a 1-lb. cut. Shellac should be thinned only with denatured ethyl alcohol (often identified as "shellac thinner"). Here are directions for common thinning requirements:

    To Reduce Shellac:

    4-lb. cut to 3-lb. cut - add alchohol - 1/2 pt. to 1 qt. shellac
    4-lb. cut to 2-lb. cut - add alchohol - 3/4 qt. to 1 qt. shellac
    4-lb. cut to 1-lb. cut - add alchohol - 2 qts. to 1 qt. shellac
    3-lb. cut to 2-lb. cut - add alchohol - 3/4 pt. to 1 qt. shellac
    3-lb. cut to 1-lb. cut - add alchohol - 3 pts. to 1 qt. shellac
    When buying orange shellac for a large project, be sure to buy enough material to do the entire job. Check the lot numbers (a code indicating date of manufacture, usually printed on the bottom of the can) to make sure all are the same. If all cans are not from the same lot, they should be blended before use because orange flake shellac can vary from crop to crop. Matching problems can result if new material must be bought to complete a large application like shellacking a paneled room. This can be avoided by calculating requirements in advance. The problem does not exist, of course, with white (clear) shellac.

    Applying Shellac

    It is best to apply shellac at low humidity and at room temperature. If humidity is high, a whitening or "blushing" of the film may occur due to vapour condensation on the surface cooled by the evaporation of alcohol. Normally this should disappear as the film dries. If extreme humidity causes it to persist, this can usually be corrected by lightly brushing alcohol over the affected areas. This releases the moisture trapped in the film.

    Shellac is easy to apply but there are a few tricks involved in brushing that can be quite easily mastered by any inexpereinced wood finisher.

    Work with a full brush and just before your film "sets" (ie, when shellac is still wet but no longer flowing), go back over it lightly with the tip of the brush to take out any bubbles.
    If you discover a missed spot (a "widow"), do not attempt to touch it up. Wait for the next coat and catch it then. Brushing after the coat "sets" will lift or wrinkle the finish.
    Proper surface preparation is the key to good results with shellac as it is with any finish. With new wood, the last sanding should be done with a fine paper to remove the wood fibres loosened by coarse papers used on first cuts. All dust must be removed with a tack cloth.
    When finishing old floors, extra care should be taken to remove all traces of wax. Any wax left on the old surface will impair the adhesion of the new shellac finish.
    Finishing and Refinishing Wood Floors

    Shellac gives a beautiful long-wearing finish that is easy to maintain and won't yellow or darken with age.

    New Floors: Sand smooth using a floor sanding machine. On the first sanding use a 50 grit paper followed by a 100 grit paper for the final cut. Remove all dust between each sanding and after the final sanding. Apply 3-lb. shellac either with a brush or an pad applicator, following the grain of the wood. Always work with a full brush. Do 2 or 3 board widths at a time and avoid excessive brushing. Allow the first coat to dry for 2 hours then hand-sand very lightly with a 100 grit sandpaper and afterwards wipe the surface with a tack rag. Apply the 2nd coat of shellac. (After about 4 hours this 2nd coat will be hard enough to walk on.) For a fuller finish or for heavy wear areas, a 3rd coat is recommended. For the 3rd coat apply 3 hours after the 2nd coat. However allow this coating to dry overnight before subjecting the floor to traffic.

    Refinishing Old Floors

    Sand the old floor smooth using a floor sanding machine. For the initial sanding use a 20 grit sandpaper to remove the old finish; for the 2nd sanding use 40 grit paper; and or the final sanding use a 100 grit paper. Remove all the accumulated dust between each of the sandings and after the final sanding. Apply the shellac as recommended above in the "New Floors" section.

    Staining Floors

    If new or refinished floors are to be stained, water or quick-drying stains are preferable because they have less tendency to streak or lap, although oil stains can be used. Make sure the stain is completely dry before applying the shellac. Oil stains should dry at least overnight before shellacking.

    On pine or other soft woods, a 1-lb. wash coat of shellac is recommended before staining to give the wood uniform porosity throughout.

    Retouching Old Floors

    After adequate surface preparation (hand-sanding of worn spots and removal of old wax) shellac may be applied with good results over old shellac, varnishes (except urethanes) and lacquers. Generally, two 3-lb. coats will do the job. Aerosol shellac is convenient where small worn areas are involved. Two or more coats with one-hour drying time between coats are recommended. Allow 4 hours after the final coat before subjecting your floor to heavy traffic.

    Waxing Shellacked Floors

    Allow 24 hours drying after applying the last coat of shellac, then apply a good quality paste wax and buff to a gleaming shine. This application of wax will actually increase water and wear resistance.

    Finishing and Refinishing Furniture, Cabinets, Woodwork, Trim and Wall Panelling

    Finishing New Wood

    Two coats of 3-lb. shellac gives a beautiful velvety sheen. Apply the shellac using a brush, applicator or pad, following the grain of the wood. Remember to always work with a full brush. Avoid excessive brushing. Let the first coat dry for 2 hours. Hand-sand lightly with 220 grit sandpaper; then wipe with a tack cloth. Apply the 2nd coat of shellac. Allow this to dry for 3 hours before applying a 3rd coat, if required. A dull finish can be achieved by steel-wooling the final coat. Do not place heavy objects on a newly shellacked surface for at least 48 hours.

    Refinishing Furniture and Cabinets

    When using shellac for refinishing old furniture and antiques, orange shellac is often preferred over the white because of its rich amber tone. Furthermore, orange shellac was likely the product used when the antique was originally finished.

    The first step is to remove the old finish with a varnish remover, following the manufacturer's directions. Allow the piece to dry, then sand it smooth using a 100 grit sandpaper and then remove the dust with a tack rag. If the wood has not been previously stained, apply the shellac as directed under "Finishing Furniture and Cabinets."

    You can remove a previous stain with wood bleach. Let the peice dry completely and then reapply your stain. On open grain woods (oak, mahogany, walnut, etc.), if filler is to be used, first tint the filler to the desired colour. Oil stains may be used but allow at least overnight drying before shellacking. Apply two coats of shellac as directed under "Finishing Furniture and Cabinets."

    French Polishing

    For the craftsman who desires the most beautiful and lasting of all finishes, French Polishing is recommended. The surface should be thoroughly sanded and stained as directed above and then must be allowed to completely dry. Using a 1-lb cut of shellac (see thinning directions) and a soft lintless cloth rolled into a ball, wipe the shellac onto the wood. Dip the ball into the shellac and rub on the wood in rapid straight strokes, exerting only light pressure. After one hour drying time, rub with 4/0 steel wood or 240 grit sandpaper and then remove any dust with a tack rag. Continuous coats are applied with sanding or steel wooling every third coat, until a light glow begins to appear. If there are hair-line cracks, sprinkle very fine pumice stone very lightly on the surface between early coats. The following coat combines with the pumice to fill the wood.

    After the first few coats, when a faint sheen begins to develop add several drops of boiled linseed oil or pure olive oil to the shellac. Continue applications as before, but with a rotary motion. Add more oil by degrees with subsequent coats. Ordinarily 8 to 12 coats are required for this technique. The result will be a superb, deeply glowing finish that with ordinary care will last for generations.

    All-Wax Finish

    Applying an all-wax finish to floors or furniture without an initial sealing coat of shellac is a mistake. Dirt and grit will work through the wax film and penetrate the open grain of the wood, imparting a dirty gray cast. To prevent this, the pores should first be sealed with one coat of 3-lb shellac. Allow 2 hours drying time, sand with 100 sandpaper and remove all dust. Apply two coats of paste wax and buff.

    Undercoat for Varnish

    One coat of a 3-lb. shellac serves as an excellent undercoat for conventional varnishes. (Do not use under urethanes). Shellac's quick drying shortens the finishing cycle, and its sealing action reduces the quantity of varnish required. It also ensures a lighter overall finish. Shellac bonds both with the wood and with standard finishes, making a foundation for a durable finish.

    Wash Coat Under Stains

    Soft woods like pine and cedar should receive a 1-lb. "wash coat" (see thinning directions) of shellac prior to applying stain. The wash coat seals the wood pores to give a controlled penetration of the stain and thus make the staining uniform. Allow this wash to dry one hour, sand lightly with a fine sandpaper or steel wood, then remove all dust with a tack rag before staining.

    Sealing Drywall (Sheetrock, Wallboard), Cured Plaster, Old Painted Walls, Wallpaper

    One coat of 2-lb. or 3-lb. shellac before painting seals these porous surfaces, prevents suction and assures a smooth uniform coat of paint, with no "high" or "low" spots.

    Sealing Drywall Before Papering

    One coat of 3-lb. shellac seals the surface of new drywall so the wallcovering can be removed at a later date without ruining the drywall facing paper.

    Sealing New Wood Before Painting

    One coat of 3-lb. shellac seals the pores of soft woods such as pine and cedar so the finish paint or enamel goes on evenly, without uneven penetration, which would leave a mottled or uneven finish.

    Sealing Knots, Sappy Streaks In New Wood

    Nothing seals off knots and sap in new wood like shellac. Depending on how green the wood is, one or two coats of 3-lb shellac will seal them off so they can't bleed into the finish coat to ruin it.

    Sealing Spackled, Stained Areas

    Shellac brushed on or sprayed seals off Spackled cracks and nail holes and stains in walls and ceilings. The new paint will go on uniformly and patched areas won't show up as "dead" spots. Stains won't bleed through painte as well.

    Exterior Spot Sealing

    Although not recommended for general exterior use, one or two coats of shellac seals knows, sappy streaks, puttied nail heads and stains. The shellac film must be covered with an exterior paint.

    Sealing Damaged Asphalt

    Prior to patching asphalt, one or more coats of 3-lb. or 4-lb. shellac will seal off oil stains (actually oil-eaten holes) to prevent residual oil from dissolving the new surfacing material.

    Trees and Shrubs

    Apply shellac on pruned branches to seal in the sap and stop the ends from bleeding.

    How To Maintain A Shellac Finish

    A shellac finish is easily maintained by cleaning the surface with a damp rag or by waxing. Where stubborn stains are involved, use a mild soap and water.

    If shellac has been water spotted, the discoloration can usually be removed by rubbing gently with an alcohol-dampened rag. If damage is too severe for correction using this remedy, or where the spot is the result of a burning cigarette or other physical damage, remove the old film in the affected area by sanding. Then apply two or more coats of shellac. Use either an aerosol shellac or a 3-lb. liquid shellac. Allow to dry, then buff with no. 00 steel wool until the new finish blends into the old.

    Waxing a shellacked surface with a good paste wax will help prevent water rings or other discoloration from cold beverage glasses, flower pots and the like. The shellac should dry for at least 24 hours before applying the wax. All waxes contain a product called carnuba. Carnuba gives the wax its hardness and its ability to resist scuffs, etc. The higher the carnuba content, the harder the wax. One product currently on the market that has a high carnuba content is a wax called Treewax.