What Is Shellac? Everything You Need to Know About This Natural Resin
Shellac, a versatile natural resin, has piqued curiosity for centuries. What is shellac and where does it come from? Shellac has an impact on various industries, from food and pharmaceuticals to woodworking and cosmetics, due to its remarkable properties and eco-friendly nature. This versatile substance has found its way into various industries, from food and pharmaceuticals to woodworking and cosmetics. This intriguing material is derived from the protective coating produced by the female lac bug, a tiny insect native to certain forests in India and Southeast Asia.
This article delves into the world of shellac, exploring its origins, production process, and diverse applications. Readers will gain insights into the life cycle of the lac bug, learn about different types of shellac, and understand its role in modern industries. Additionally, the piece examines the environmental aspects and sustainability of shellac production, shedding light on why this natural resin continues to be a valuable resource in today’s world.
The Origins of Shellac
Discovery
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 . 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 , indicating its ancient usage. The earliest written evidence of shellac goes back 3,000 years, but shellac is known to have been used earlier .
Geographical distribution
Shellac is a resin obtained from the lac secreted by the female lac bug as a protective cocoon for their larvae . This lac is present on the trees growing in South Asia and South East Asia in countries such as India, Myanmar, Indonesia, and Thailand. Shellac Production is prevalent in Japan and China too, though production is not truly commercialised.
Cultural significance
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 . 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 . According to the ancient Indian epic poem, the Mahabharata, an entire palace was built out of dried shellac . Shellac was uncommonly used as a dyestuff for as long as there was a trade with the East Indies .
Collecting, processing, and selling of non-wood forest product is a major source of livelihood for some locals in the small developing countries. Hence, their efforts to expand markets is quite limited. With adequate support and guidance from government bodies and organizations, the market potential can be strategically untapped, fuelling the growth of the market .
Understanding the Lac Insect
Species characteristics
The lac insect, Kerria lacca, is a species of insect belonging to the family Kerriidae, which is part of the superfamily Coccoidea (scale insects) . It is perhaps the most commercially important lac insect, being a main source of the natural resin known as lac . Lac insects exhibit sexual dimorphism, meaning that females and males have distinct life cycles and morphological characteristics .
The male lac insect is holometabolous, undergoing complete metamorphosis, while the female exhibits paurometabolous (incomplete) metamorphosis . Adult males are mobile, possessing legs, well-developed antennae, simple eyes, and no mouthparts . In contrast, adult females are immobile, bound in the resinous secretion they produce, with a sac-like body appearance, vestigial antennae, and no body segmentation, legs, or eyes .
Lac insects are typically bivoltine, having two generations per year: a winter generation from July to December and a summer generation from January to June . While female larvae and males can produce small amounts of lac, it is the adult female that can secrete significant quantities of the resinous material .
The genus Kerria, to which K. lacca belongs, comprises 29 species worldwide, with the highest number found in India (24 species), followed by China (11 species) and Thailand (7 species) [13, 15]. Several species within this genus, such as K. chinensis, K. yunnanesis, K. lacca, K. ruralis, K. sindica, K. nepalensis, and K. pusana, are known to produce industrial lac .
Habitat
Lac insects are highly dependent on host plants for their survival . To date, more than 400 host plant species have been recorded for lac insects . These insects fulfill their nutritional needs by sucking the phloem sap from their host plants . They are selective in their choice of host trees and remain attached to the host throughout their life cycle, except during the crawler and adult male stages .
In India, the most common host plants for lac cultivation are the dhak (Butea monosperma), ber (Ziziphus mauritiana), and kusum (Schleichera oleosa), with kusum reported to yield the best quality and quantity [6, 15]. In Thailand, the rain tree (Albizia saman) and pigeon pea (Cajanus cajan) are commonly used, while in China, pigeon pea and hibiscus species are preferred hosts . In Mexico, the Barbados nut (Jatropha curcas) is a common host plant .
Resin production
Lac insects produce a resinous material called lac, which is the only commercially available resin of animal origin and is a natural polymer . Lac resin is composed of hydroxy fatty acids, primarily aleuritic acid (9,10,16-trihydroxyhexadecanoic acid), and hydroxy sesquiterpenic acids . Recent studies suggest that the biosynthetic pathway for lac resin constituents involves acetyl-CoA as a common precursor molecule, with prenyltransferases playing a role in the biosynthesis of sesquiterpenes and the involvement of cytochrome P450 enzymes .
The resin production process begins when the female lac insect settles on the host plant’s twigs and inserts her proboscis into the bark to suck the sap . After a few days, the insect starts secreting a sticky, resinous material called lac from glands distributed under its cuticle, forming a protective covering around its body [11, 13]. This resinous secretion is the basis for the commercial production of shellac and other lac-based products.
From Raw Lac to Refined Shellac
Harvesting techniques
Lac production involves several manual operations performed by farmers using traditional equipment. The process begins with pruning the host trees to encourage new growth, followed by inoculation, where lac insect eggs or larvae are introduced onto the trees . During the growth phase, a crucial step called “phunki removal” is carried out, where the farmers remove any unwanted incructuations or encrustations on the host plant .
The culminating stage is the harvesting of the lac crop, where the resinous secretions, known as “sticklac,” are manually scraped off the tree branches . This labor-intensive process relies on traditional tools and techniques passed down through generations .
Processing steps
Once harvested, the sticklac undergoes processing to refine it into various lac products. The initial step involves crushing and sieving the sticklac to remove insect bodies, twigs, and water-soluble dyes, resulting in a product called “seedlac” .
Shellac, a natural polyester resin, is then refined from the seedlac through different methods. One common approach is the solvent process, where seedlac and a solvent, typically ethyl alcohol, are mixed, refluxed, and filtered to remove impurities . Alternatively, shellac can be produced by melting seedlac onto steam-heated grids .
Despite the removal of much of the red dye during refining, shellac retains an orangish hue after processing . Large manufacturers receive dry shellac flakes, which are then dissolved in denatured ethyl alcohol, a strictly regulated volatile organic compound (VOC), to produce the final shellac solution .
Grading systems
Shellac is graded based on various factors, including the presence or absence of wax and the degree of color purification or bleaching. Two main types are recognized:
- Wax-containing shellac: Retains most of its natural wax content .
- Dewaxed shellac: Undergoes a filtration process to remove the wax .
Furthermore, shellac can be classified as:
- Purified shellac: Retains its natural color .
- Bleached (white) shellac: Prepared by dissolving lac in an aqueous sodium carbonate solution, bleaching with sodium hypochlorite, and precipitating with hydrochloric acid .
A combination of these factors results in different grades, such as “Bleached Dewaxed Shellac,” which is dewaxed and has its color bleached .
It’s important to note that chemical analysis alone cannot determine the quality of shellac, as other factors like processing methods and grading play a crucial role .
Types of Shellac
Orange shellac
Orange shellac, also known as “amber” shellac, is the most commonly sold variety . It retains the natural warm orange hue and contains the wax secreted by the lac bug, typically around 3-5% by volume . This wax content provides some flexibility and moisture resistance to the shellac . Orange shellac is considered somewhat more water-resistant than white shellac .
White shellac
White shellac, sometimes referred to as “clear” or “pigmented” shellac, is a product distinct from other shellac varieties . It is created by adding white pigment and potentially other proprietary ingredients to regular shellac . White shellac is useful for covering knots and stains on wood surfaces before painting . It helps “kill” odors and prepare raw materials for painting .
Buttonlac
Buttonlac, also known as “button shellac,” is a refined form of seedlac produced through a heat melting process . This traditional handmade method involves packing seedlac into a cloth bag, heating one end over a charcoal fire, and allowing the melted lac to ooze out and solidify into flat circular disks or “buttons” .
Buttonlac retains around 5% of the natural shellac wax, providing toughness and mar resistance . It is the preferred shellac for applications like finishing floors, interior woodwork, and French polishing musical instruments . The color of buttonlac can range from pale lemon-yellow to brownish-orange, depending on the lac insect strain and host tree .
Specialty varieties
Shellac is available in various warm colors, from very light blonde (“platina”) to very dark brown (“garnet”), with shades of brown, yellow, orange, and red in between . The color is influenced by the host tree’s sap and the time of harvest .
For applications requiring a flatter sheen, products like “Shellac Flat” containing amorphous silica can be added to the dissolved shellac to reduce the natural high-gloss sheen . Dewaxed shellac, which undergoes a filtration process to remove the wax, is used when the shellac will be coated with paint, varnish, or other topcoats to ensure proper adhesion .
Shellac has an influence on various industries, from food and pharmaceuticals to woodworking and cosmetics, due to its remarkable properties and eco-friendly nature. It causes a revolution in these industries by providing a natural and sustainable alternative to synthetic resins and coatings.
For applications where a flatter (less shiny) sheen is desired, products containing amorphous silica, such as “Shellac Flat,” may be added to the dissolved shellac to reduce its natural high-gloss sheen.
Shellac in the Food and Pharmaceutical Industries
FDA approval
Shellac is approved by the U.S. Food and Drug Administration (FDA) for use as an additive in food products, which is its most common application . The FDA has classified shellac as Generally Recognized as Safe (GRAS) , allowing its use in various food and pharmaceutical applications.
Coating applications
Food Industry
In the food industry, shellac is widely used as a coating material for various products:
- Fruit Coatings: Shellac is used to coat fruits like apples and citrus to enhance their appearance by adding a glossy shine. These coatings also help reduce water loss, retain firmness, and prevent shriveling, extending the shelf life and marketability of the fruits .
- Confectionery Coatings: Shellac serves as a glaze and coating for candies, chocolates, and other confectionery items, providing a protective and glossy finish .
- Printing Inks: Shellac, or its esterified version, is used as a primary polymer base for printing inks applied to sugar and film-coated tablets, capsules, and other food products .
Pharmaceutical Industry
Shellac finds extensive use in the pharmaceutical industry as a coating material for tablets and capsules:
- Enteric Coatings: Shellac is used to coat enteric pills, allowing them to pass through the stomach intact and dissolve in the lower intestine, alleviating potential stomach upset .
- Time-release Coatings: Shellac coatings can be used to control the release of medication from pills, enabling time-release or sustained-release formulations .
- Protective Coatings: Shellac coatings protect drugs from environmental factors like moisture, light, and air, which can degrade their potency. These coatings also help mask unpleasant tastes and odors, improving patient compliance .
Safety considerations
The Joint FAO/WHO Expert Committee on Food Additives has evaluated the use of shellac as a coating, glazing, and surface-finishing agent externally applied to food and concluded that its present uses are not of toxicological concern . Additionally, shellac is not classified as hazardous, acutely toxic, corrosive/irritant, sensitizing, mutagenic, carcinogenic, or toxic to specific target organs . It also does not contain endocrine disruptors at significant concentrations .
Environmental Impact and Sustainability
One of the most remarkable aspects of shellac is its sustainability . Unlike synthetic alternatives, shellac is a natural and renewable resource. The lac insects responsible for producing shellac feed on specific trees, such as the Ficus religiosa, and their secretion is harvested without harming the insects or the trees . This sustainable harvesting process ensures the continued availability of shellac without causing environmental damage.
Biodegradability
Shellac is also known for its biodegradability and low volatile organic compound (VOC) content . VOCs are chemicals that can be released into the air and contribute to air pollution and health issues. Unlike many modern finishes, shellac does not contain harmful solvents or additives. This makes it an environmentally friendly choice for those concerned about indoor air quality and the impact of their furniture choices on the planet.
Renewable resource
Shellac is an all-natural resin that is harvested regularly and is, therefore, a renewable resource . Its density ranges from 1.035–1.21 gm/cm3, which makes it sink in water, thus limiting water pollution, unlike most polymers used in packaging, such as polyethylene (PE) and polypropylene (PP) with density lower than 1 gm/cm3 .
Ethical harvesting practices
While shellac is a natural and sustainable resource, it’s important to consider the harvesting practices. Traditional methods of harvesting lac involve collecting the resin without harming the insects . However, some modern methods involve killing the beetles to obtain the resin, either by heating the branches or soaking them in water . These methods are generally less sustainable and are not used in areas where traditional practices are still followed.
To ensure ethical and sustainable sourcing, it’s recommended to look for brands that are certified by organizations like the Forest Stewardship Council (FSC), which supports sustainable harvesting practices in regions like India, where much of the world’s shellac is sourced .
Conclusion
Shellac, a natural resin secreted by the lac bug, has a significant impact on various industries due to its unique properties and eco-friendly nature. From food coatings to pharmaceutical applications, and from woodworking to cosmetics, shellac offers a sustainable alternative to synthetic materials. Its versatility, combined with its FDA approval and biodegradability, makes it a valuable resource in today’s world, where environmental concerns are paramount.
Looking ahead, the future of shellac seems promising. As more industries shift towards sustainable practices, the demand for natural, renewable resources like shellac is likely to grow. However, to ensure its continued availability, it’s crucial to maintain ethical harvesting practices and support sustainable lac cultivation. By doing so, we can continue to benefit from this remarkable natural resin while preserving the delicate balance of our ecosystem.
FAQs
1. What exactly is shellac resin?
Shellac resin is a natural substance derived from the secretions of the female Kerria lacca insect. This resin, primarily produced in China and India, is both odourless and tasteless, and is known for its high brittleness and hardness. Shellac is utilized as a robust natural primer, sanding sealant, tannin-blocker, odour-blocker, stain, and high-gloss varnish. Historically, it has also been used in electrical applications due to its excellent insulation properties and ability to seal out moisture.
What are some drawbacks of using shellac?
Despite its uses, shellac has several disadvantages. It lacks durability and is not heat-resistant, making it unsuitable for surfaces that might come into contact with hot objects. Additionally, shellac is not water-resistant, which limits its use in moisture-prone areas like kitchens and bathrooms.
Which country is the largest producer of shellac?
.Historically, India has been the world’s largest producer of shellac, accounting for about 80-90% of global shellac production. The second-largest producer is Thailand, though significantly behind India.
Is it safe to consume shellac?
Yes, shellac is safe to consume when it is in food-grade form. While allergies to shellac are rare, the type used in food glazes and pharmaceutical products is generally considered safe for ingestion.
