Finishing Materials Used in Restoration
Authentic and traditional finishing materials should be used in furniture restoration. Traditional finishing materials, as the name suggests, are those that have been used for a very long time and are made using old technologies based on natural materials. Modern finishing materials are made using mostly synthetic materials, which are not always proven to be durable, and repeated finishing is possible only by mechanically removing the old coating. Traditional finishing materials not only retain their properties for a long time, but are also generally easy to restore. The reversibility principle is one of the most important in restoration, therefore irreversible synthetic materials should not be used.
In the past, furniture finishing used varnishes that used shellac, copal, rosin, sandarac, drying oils, and natural waxes as binders. From the beginning of the 19th century to the 1950s, the most popular were shellac finishes, less often furniture finished with beeswax or oil varnish.
Natural oils.
The main raw material for the production of varnishes, oil paints, enamels and emulsions are various natural oils, which are obtained from purified plant seeds by pressing or extraction.
Chemically, natural oils are mainly esters of glycerin and monounsaturated fatty acids. The different properties of oils depend mainly on the composition and structure of the fatty acid radicals present in the oils. The main property of oils that determines their suitability for use in finishing materials is their drying ability and the ability to form a hard and elastic finish.
The drying of oils is a very complex process. Initially, oxygen from the air is added to the free radicals of unsaturated fatty acids, i.e. oxidation. Then, as the chemical transformations of the coating layer continue, a polymer is formed, and the coating layer gradually hardens, becomes immobile and chemically resistant.
According to the drying rate, natural oils are divided into three groups: drying oils, slow-drying oils and non-drying oils.
Drying oils are tung oil, linseed oil and hemp oil. Tung oil dries the fastest, so it is used to make quick-drying oil varnishes and varnishes. An undesirable circumstance is that the finishes, in which the main binder is tung oil, age relatively quickly, become brittle and crack. Therefore, other binders and plasticizers are often added to the finishing compositions in addition to tung oil.
Natural waxes.
Beeswax is a fat-like, white substance in its pure form with a characteristic honey aroma. It is secreted by bees from wax glands. Becomes plastic at 35°C. Melting point 62—68°C, boiling point - 100°C. It is well soluble in turpentine, essential oils, gasoline, ether, poorly soluble in ethyl alcohol. It is not recommended to use it in its pure form for furniture finishing, because it has a relatively low moisture resistance, therefore it is modified with paraffin, linseed oil, rosin or carnauba wax.
Natural resins.
Natural resins are solid or semi-solid viscous substances. Characteristic properties of resins are their solubility and ability to form transparent, shiny solid coatings that have good adhesion to various surfaces. Depending on the solubility, resins are sometimes divided into alcohol-soluble and oil-soluble resins.
Rosin(colophony) is a dry crystalline substance. It is obtained from coniferous tree resin by distilling off essential oils, turpentine, etc. Rosin is light yellow to brown in color, its melting point is 60—70°C, and its density is 1.09 g/cm3. Rosin is soluble in alcohol, acetone, turpentine, benzene and partly also in gasoline. In its pure form, rosin is not suitable as a binder, because it forms very brittle, heat-resistant coatings, which become sticky when heated slightly.
Therefore, in the production of finishing materials, rosin processing products are more widely used - its resinous acid salts and esters. The most widely used are rosin glycerin esters, or so-called. rosin esters. These are light, transparent resins with a melting point not lower than 70°C. They are well soluble in oils, turpentine and aromatic hydrocarbons, but almost insoluble in alcohol. Rosin glycerin esters are widely used together with other resins in the manufacture of oil and nitrocellulose varnishes and enamels.
Similar to rosin is abietic resin, which is obtained by oxidizing spruce resin at high temperatures. Abietic resins are relatively heat-resistant, melt at 95—100°C and are well soluble in alcohols. However, they are dark in color and form relatively weak finishes with low gloss. Abietic resins are used together with other binders to make dark nitrocellulose and spirit varnishes. A product of coniferous resin processing is the so-called. oxyterpene resins, which are obtained by oxidizing turpentine and evaporating the volatile constituents. At room temperature, these resins
Shellac (English: shellac, German: schellack, Russian: шеллачный лак; шеллак, French: gomme-laque) is a resinous secretion produced by the lac bug (Coccus lacca) on the young shoots of certain tropical trees in India and Thailand. The lac bug is a scale insect, and the resin is produced as a protective coating for the insect's larvae.
Shellac is harvested by scraping the resinous encrustations from the host trees. The raw shellac is then processed to remove impurities and to produce various grades of shellac.
Shellac is a natural, non-toxic material that is used in a variety of applications, including:
Wood finishing: Shellac is a traditional wood finish that is prized for its durability, clarity, and warmth. It is available in a variety of colors and finishes, and can be applied with a brush, roller, or sprayer.
Food additive: Shellac is used as a food additive to give foods a shiny coating and to protect them from moisture loss. It is also used as a glazing agent in confectionery.
Pharmaceutical ingredient: Shellac is used in the manufacture of some pharmaceutical products, such as enteric coatings for tablets and capsules.
Cosmetics: Shellac is used in some cosmetics, such as nail polish and hairspray.
Shellac is a versatile material with a wide range of applications. It is a natural, non-toxic material that is safe for use in food, pharmaceuticals, and cosmetics.
Here is some additional information about shellac:
Solubility: Shellac is soluble in alcohol, acetone, and other organic solvents. It is insoluble in water.
Melting point: The melting point of shellac is 75-85°C.
Density: The density of shellac is 1.04-1.18 g/cm3.
Chemical composition: Shellac is a complex mixture of organic compounds, including resin, wax, and a small amount of protein.
Here are some of the benefits of using shellac:
Durability: Shellac is a very durable finish that can last for many years.
Clarity: Shellac is a clear finish that will not yellow or darken over time.
Warmth: Shellac has a warm, natural look that is often preferred over other finishes.
Non-toxic: Shellac is a non-toxic material that is safe for use in food, pharmaceuticals, and cosmetics.
Here are some of the drawbacks of using shellac:
Cost: Shellac can be more expensive than some other finishes.
Solubility: Shellac is soluble in alcohol and other organic solvents, which can make it difficult to clean up.
Fire hazard: Shellac is a flammable material, so it should be used with caution.
Sandarac (English: sandarac, sandarach, German: sandarak, Russian: сандарак, сандарака) is obtained from the resin of Callitris guadrivalis and other coniferous trees growing in Africa and Australia. Until recently, sandarac was considered the best resin for making spirit varnishes used for finishing the bodies of stringed musical instruments.
Sandarac is prepared in the form of hard, light yellow or reddish grains. Its density is 1.05-1.10 g/cm3 and its melting point is 110-145 °C. Sandarac is soluble in ethanol and partially in turpentine. Sandarac varnishes form hard coatings with very good resonance properties.
Copal (English: copal, German: copal or kopal, Russian: копал) is a resin of tropical plants. After heat treatment (280-320 °C) and separation of volatile substances, the resin is relatively soluble in organic solvents and mixes well with vegetable oils. Copal was once considered the best resin for making oil varnishes. Copal varnish and enamel coatings are relatively hard, with good gloss, high melting point and atmospheric resistance.
Synthetic resins (should not be used in furniture restoration) Synthetic resins are now the main binders in the varnish and paint industry. They are various organic compounds of diverse composition. The majority of synthetic resins used in finishing materials are polymers, i.e., high-molecular-weight compounds that are soluble in organic solvents or melt at elevated temperatures, mix with other binders and form durable coatings.
Oil varnishes
Oil varnishes are solutions of resins in heat-treated drying oils and solvents with the addition of siccatives. The hardening of these varnishes is a physicochemical process that involves both oxidation and polymerization reactions of the binders and evaporation of the solvents. Oil varnish coatings bond well with wood, are elastic, have medium mechanical properties, are heat and water resistant. In terms of appearance, oil varnish coatings with their matt shine lag behind coatings of other materials. Oil varnishes are used for finishing work both indoors and outdoors. Oil varnishes are classified according to the type of resin, the amount of resin and oil - the ratio and the application of the varnish. According to the type of resin, there are colophony, glyptal resin, pentaphthalic resin, copal and other varnishes. According to the ratio of resin and oil, oil varnishes are divided into: fatty varnishes, which contain 2-5 times more oil than resin, medium varnishes, which contain 1.5-2 times more oil than resin, and lean varnishes, which contain less oil than resin. Fatty oil varnish coatings are elastic and have high atmospheric resistance, therefore they are used for external finishing work. The disadvantage is the slow drying of these coatings, which takes up to three days. Medium oil varnish coatings are less elastic but dry faster. They are used for indoor and outdoor finishing work. Lean oil varnishes form hard and glossy, but atmospherically unstable coatings. These varnishes are used for finishing work indoors.
Spirit varnishes
Spirit varnishes are varnishes that consist of natural or synthetic resins dissolved in ethanol with the addition of a plasticizer. The varnishes may also contain other solvents and dyes. The solids content of spirit varnishes is 25-30%. These varnish coatings harden by evaporation of the solvents. Spirit varnish coatings have relatively low mechanical strength, low water, thermal and chemical resistance. Therefore, spirit varnishes are used for finishing objects used indoors. According to the binder used, there are shellac, colophony shellac, iditol resin, sandarac and copal spirit varnishes. Shellacs are 35-40% solutions of shellac in ethanol. They are spirit varnishes that form high-quality, highly decorative finishing coats that are elastic, hard, well sandable and polishable. Colophony shellacs are a solution of shellac and colophony in alcohol with the addition of a plasticizer. In terms of quality, colophony shellac coatings are not much inferior to shellac coatings, however they are slightly more fragile. Iditol resin varnishes are a 30% solution of iditol resin in alcohol. Iditol resin varnishes are used as a substitute for shellac. They form fairly durable glossy coatings, but with low lightfastness. When exposed to light, iditol resin varnish coatings yellow over time. The most widely used wood products are cresol iditol resin varnishes and phenolic iditol resin varnishes. Sandarac and copal varnishes are solutions of natural sandarac and copal resins in alcohol. In terms of mechanical strength and elasticity, their coatings are inferior to shellac coatings. Sandarac and copal varnishes have good resonance properties, therefore they are used for finishing musical instruments.
Polishes
Polishes are used to smooth and polish the surface of finishing coats. Polishes are solutions of binders in organic solvents. Unlike varnishes, polishes contain more or less active solvents. This prevents the possibility of quickly dissolving the varnish layer and the formation of so-called "burning" during the polishing process. The binders