A Talk About Shellacs, Gums and Varnishes

Shellac Solution Without Wax

To the shellac solution separated from the vegetable wax, a medium is added which fully takes the place of the wax as regards pliancy and polishing qualities, without exhibiting its undesirable after effects. Such a medium has been found in the essential oils, especially in oil of rosemary. The production of the new polish is, for instance, as follows: Dissolve 20 kilos of shellac and 4 kilos of gum benzoin in as little 95 or 96 per cent spirit as possible, with the addition of 1 kilo of oil of rosemary. The concentrated solution is now repeatedly filtered over fresh stick lac until the vegetable wax contained in the solution is completely abstracted and the solution has become perfectly clear. A description of lac may not be amiss in this connection. “Stick lac” is one of the five grades that are known to commerce, the others being seed lac, shellac, button lac, and garnet lac. Stick lac is the crude product as it comes from the trees. By this it is not meant that it is a product of any tree, although the tree or trees upon which it is found does give a gummy or resinous sap. An insect, scientifically called the Coccus lacca, and the female only, punctures the bark of the tree, and the sap is utilized by the insect to form cells with and in which it lays eggs and itself becomes embedded, breathing by means of fine filaments which are sent to the surface for the purpose, because the insect becomes buried in the gum, head and all. After having laid its eggs the insect dies. In due course the eggs hatch out and the young insects swarm out and over the neighbouring twigs, and repeat the round of egg laying and dying, until finally an end comes to the race on that particular tree when its vitality has been drained and it succumbs. As with the San Josescale, the lac insects are transported from place to place by birds and other agencies. The twigs covered with lac are gathered and broken into bits about two inches long, and are carried from the jungles to the nearby towns, where the gum is removed from the wood in a crude manner by the natives. The lac is very brittle; hence it is easily removed from the sticks by passing a roller over it, crushing the gum and leaving the twigs clean of it. Then the lac is thrown into tubs of water and natives get in and tread the gum into a mass, the water being warm. After a time, the water becomes quite clear, the colouring matter having been removed. This gives us “seed lac.” The liquor is boiled down dry, and the resulting mass, solid, is made into cakes and sold as lac dye. Formerly this was used for dyeing purposes but with the advent of the aniline dyes it fell into disuse. Seed lac is mostly made into the other lac products.

Seed Lac and Shellac

Shellac (shell lac, being in the form of scales or shells) is the principal lac product and the variety used in making the commonly known shellac varnish. Shellac is made from seed lac in this way: The seed lac is dried and placed in bags made of cotton cloth of medium texture. Two men take hold of the bag of seed lac, one at each end, and hold it in front of a charcoal fire; the heat soon melts the lac, and it flows out of the bag, the men assisting the operation by twisting the bag so as to squeeze out the liquid lac. The lac drops out into a trough placed in front of the fire, a cylinder of wood or other material, with the upper half covered with brass, or it is made of porcelain, or perhaps of the finely polished stem of the plantain. This cylinder is placed in a somewhat inclined position, and the operator, taking up a ladle full of the molten shellac from the trough, pours it on the upper surface of the cylinder, while an assistant by means of a leaf of plantain spreads the melted material over the surface of the cylinder. It soon cools there, after which it is stripped off with a knife and is ready for sale as shellac gum. Button shellac differs from shellac only in form. Garnet lac is similar to button lac. Neither is as good a quality as the shellac variety. Either of the lacs may be used for shellac varnish making but the orange shellac is best. The best quality of shellac has a pale and bright orange colour, being known as orange shellac. Crude stick lac contains 66 per cent resin, 6 per cent of wax, 6 per cent of gluten, and 10.8 per cent of colouring matter after being freed from the wood. Five distinct resins have been separated from shellac: resin soluble in alcohol and ether; resin soluble in alcohol, but insoluble in ether; resin slightly soluble in alcohol; a crystallizable resin, and an uncrystallisable resin. These constitute about 80 per cent of the shellac There are in addition fatty matter, wax, gum and colouring elements. Bleached shellac, or white, may be made in two or three ways. One method is to boil orange shellac in a weak solution of carbonate of potash, and when dissolution is affected to collect the shellac, melt it under water, and while soft to pull it until it assumes a satiny appearance. Another way is to boil the shellac in a weak solution of potash and while it is in a melted state pull and work it like you would taffy candy until the desired degree of whiteness is obtained. Then remelt the shellac and repull it in clean warm water. White shellac always contains more or less water, hence for many purposes is not as good as the orange. Always dry bleached shellac before using. Another thing is not generally known and that is, bleached shellac deteriorates with age, becoming insoluble in alcohol or borax. A good recipe for making a colourless shellac solution for varnishing paintings and prints is as follows: Dissolve 150 grams of shellac in a litre of alcohol by the aid of gentle heat in a water bath. Stir in about 150 grams freshly burned animal charcoal and bring the mixture to a boil, maintaining it at the boiling temperature about ten minutes. Filter a small portion and, if not absolutely colourless, add a little more charcoal and boil again. After again testing, if found to be quite free from colour, first strain through silk and subsequently filter through paper, and add a little castor oil, to insure elasticity. While the process for bleaching shellac is easily described and for individual uses easily accomplished, yet on a commercial scale it is rather more difficult. There are at least twelve operations essential in shellac bleaching, namely:

Crushing the raw material to a powder, so that it will become more readily soluble in the alkaline solution.

Separation of the colouring principle from the gum resin. Preparation of the bleaching agent, or hypochlorite of potash or soda. Treatment of the liquefied shellac by the bleaching agent.

Diluting the bleached shellac alkaline solution in water. Preparing the sulphuric acid for neutralizing the alkaline solution of shellac.

Neutralizing the shellac alkaline solution by the use of diluted sulphuric acid, which coincidently precipitates the bleached shellac.

Filtering the precipitate, or pulp, of bleached shellac. Malaxing the neutral pulp of bleached shellac to develop whiteness and elasticity.

Hardening and whitening process of the sulphuric acid bath, which prevents to a very great extent the white shellac turning yellow when exposed to the light.

Drying the bleached shellac.

Crushing the bleached shellac.

Thus, it may be seen that to make a good quality of bleached or white shellac on a commercial scale requires something more than a taffy-pulling match. Of course, you will know that when bleached or white shellac is bought it comes in a granulated form. Recent years saw much adulteration of shellac varnish in which rosin, the common North Carolina copal, so called, played a leading part, while the use of wood alcohol added insult to injury. One of the severest tests of a shellac varnish is made in the hands of the common house painter, on sap and knots. In by gone days the painter could carry the bottle of shellac with him and shellac or “kill,” as he called it, the knots and at once apply the priming coat of paint, and the knots would be killed. It was not the best way, for it gave the shellac no time to get dry hard. Apparently, the shellac is dry in a few moments but really it is not. Now when he tries such a trick the knots show through any number of coats of paint that he may apply. I had such a thing occur with me last summer. I shellacked some white pine knots of large size, using white shellac varnish that had been on hand for some time, though well stoppered. The knots all showed through the pure white paint, it being a parlour job.

Success in Varnishing

There is another fact that wood finishers as well as painters should be cognizant of when using shellac varnish. It is this, that unless the lumber is decidedly dry there will be bad work. It is bad enough to finish or work right over freshly applied shellac varnish, but the trouble is greatly increased if the wood is not dry. And when undry lumber is placed where heat can work on it, then the dampness will work to the surface and woe then unto the shellac or any other varnish. This is the cause of many a trouble in the finishing room. An article is finished and placed in a warm room. The heat brings to the surface the moisture in the wood and there is a dimming of the finish. Pure shellac varnish gives a harder surface than one that is adulterated with rosin. The amount of rosin in a doctored shellac may be anywhere from one-fourth to one-half the quantity of gum shellac. The rosin is finely pulverized, say five pounds of orange shellac gum and five pounds of pulverized rosin of good quality, dissolved in two gallons of wood alcohol. Better still, of course, for it is cheap enough now, use denatured alcohol. Such a varnish must be used as soon as possible after being made. Otherwise the alcohol evaporates and the gums fall to the bottom like a mass of rubber and this mass never can be redissolved. Any good shellac may become very dark with age. Certainly, it will if kept in a metallic vessel for a time. In such a case the original colour may be restored by dissolving one quarter ounce of oxalic acid in ten parts of water and adding this to one gallon of dark shellac. Nor will this treatment in any manner injure the shellac. Water shellac is useful for some kinds of work, and may be made thus: Take powdered white shellac, one pound, and powdered borax, one-half pound. Place in one gallon of soft rainwater and boil in a porcelain kettle until the shellac has nearly all dissolved. There will be a residue which cannot be dissolved. Strain through a cheese-cloth, then boil down to the desired consistency. The addition of a little alcohol will not be amiss, though it is not necessary. Eight ounces of alcohol to the gallon of varnish will give it the usual odour and help it in other ways.

Water Shellac You may mix, if you like, equal parts of the water shellac with orange alcohol shellac. This water shellac dries much slower than the pure alcohol shellac, but when dry it may be rubbed easily and save lots of sandpapering as compared with the real thing. And another matter worth considering—it will not raise the grain of wood as badly as the alcohol shellac will. For cheap work it will make a very satisfactory coating under the varnish coats. Not setting quickly like alcohol shellac; it may be brushed out smoother and hence will take less rubbing. Mixed with a strong solution of brown or white glue, according to the nature of the work in view, half and half, water shellac gives a good filler on cheap work, bearing out the varnish nicely and giving a good clean job with one coat of filler and one of cheap varnish. For finer effects, use two or more coats of varnish.

Success in Varnishing

There is another fact that wood finishers as well as painters should be cognizant of when using shellac varnish. It is this, that unless the lumber is decidedly dry there will be bad work. It is bad enough to finish or work right over freshly applied shellac varnish, but the trouble is greatly increased if the wood is not dry. And when undry lumber is placed where heat can work on it, then the dampness will work to the surface and woe then unto the shellac or any other varnish. This is the cause of many a trouble in the finishing room. An article is finished and placed in a warm room. The heat brings to the surface the moisture in the wood and there is a dimming of the finish. Pure shellac varnish gives a harder surface than one that is adulterated with rosin. The amount of rosin in a doctored shellac may be anywhere from one-fourth to one-half the quantity of gum shellac. The rosin is finely pulverized, say five pounds of orange shellac gum and five pounds of pulverized rosin of good quality, dissolved in two gallons of wood alcohol. Better still, of course, for it is cheap enough now, use denatured alcohol. Such a varnish must be used as soon as possible after being made. Otherwise the alcohol evaporates and the gums fall to the bottom like a mass of rubber and this mass never can be redissolved. Any good shellac may become very dark with age. Certainly, it will if kept in a metallic vessel for a time. In such a case the original colour may be restored by dissolving one quarter ounce of oxalic acid in ten parts of water and adding this to one gallon of dark shellac. Nor will this treatment in any manner injure the shellac. Water shellac is useful for some kinds of work, and may be made thus: Take powdered white shellac, one pound, and powdered borax, one-half pound. Place in one gallon of soft rainwater and boil in a porcelain kettle until the shellac has nearly all dissolved. There will be a residue which cannot be dissolved. Strain through a cheese-cloth, then boil down to the desired consistency. The addition of a little alcohol will not be amiss, though it is not necessary. Eight ounces of alcohol to the gallon of varnish will give it the usual odour and help it in other ways.

Water Shellac

You may mix, if you like, equal parts of the water shellac with orange alcohol shellac. This water shellac dries much slower than the pure alcohol shellac, but when dry it may be rubbed easily and save lots of sandpapering as compared with the real thing. And another matter worth considering—it will not raise the grain of wood as badly as the alcohol shellac will. For cheap work it will make a very satisfactory coating under the varnish coats. Not setting quickly like alcohol shellac; it may be brushed out smoother and hence will take less rubbing. Mixed with a strong solution of brown or white glue, according to the nature of the work in view, half and half, water shellac gives a good filler on cheap work, bearing out the varnish nicely and giving a good clean job with one coat of filler and one of cheap varnish. For finer effects, use two or more coats of varnish.