Pigments of the Imagination: Cochineal’s Renaissance

June 22, 2016

SAP-SUCKING SCALE INSECTS, such as cochineal, kermes and lac, are sometimes sprayed with pesticides as landscape and crop pests, and other times cultivated as beneficial insects. For example, cochineal secals have provided biological weed control in India, Australia and South Africa where imported prickly pear cactus (Opuntia spp.) hedges have escaped and become rangeland weeds. Cochineal scale insects, bred in ancient Mexico to yield 15%-30% color pigment content, have been grown in the Americas for many centuries on prickly pear cactus as a sustainable, biodegradable colorant crop yielding dyes ranging from red, yellow, orange and brown to pink, lavender and purple (depending on mordant, pH, etc.). Intensely red cochineal has a long and famous history in painter’s palettes, tapestry and fabrics, and has been used for centuries to color or stain tissues red or purple for microscope visibility in biology and microbiology labs, medicine and dentistry. Cochineal scale pigments also color selected beverages, foods (on labels as E-120 & carmine) and cosmetics like lipstick, rouge and nail polish. Biochemistry labs like the cochineal red molecule’s ability to bind or bond with proteins, nucleic acids and fats (lipids). Analytic chemists use cochineal “for photometric determination of boron, beryllium, uranium, thorium, and osmium.” At the cutting edge frontier of science, cochineal pigments are being adapted to “molecular information processing” and computing. The red pigment’s “strong photosensitization and photocurrent switching effects” are being designed into next generation optoelectronic (i.e. light, photon) devices like semiconductors, fuel cells, sensors and photovoltaic solar energy systems.

“In Latin-the indispensable language of Renaissance medical professionals—the word pigmentum signified both a pigment and a drug,” writes Amy Butler Greenfield on page 83 of the paperback edition of her meticulously researched book, A Perfect Red, which follows the parallel rise and fall of the Spanish Empire and the secretive cochineal red export trade. “Artists who made their own paints were often advised to procure cochineal from their local “Drugist” or pharmacy, advice that highlights the fact that Europeans also used cochineal as a medicine,” a practice “at least partly borrowed from ancient Mexico,” where cochineal was used to clean teeth and also dissolved in vinegar and applied as a poultice to cure wounds and strengthen bodily organs. Spain profited more from importing cochineal into Europe than from all its plundered and mined New World gold. When ancient alchemy’s metamorphosis into modern chemistry advanced to synthesizing a less expensive, wider range of brighter dye pigments, the Spanish red dye monopoly was obsoleted and the financial collapse of the steadily weakening empire allowed for a global power shift; the USA, fresh from coast to coast expansion and hot for global colonial-style conquests, easily knocked off the remnant hollow shell of the Spanish Armada in the Caribbean and Philippines in 1898.

Let’s start with cochineal and scale insects as pests, and organic control alternatives, as that is how most people encounter and view scale insects. Parasitoid wasps, lady beetles, birds and many other natural enemies provide biological control of scale insects, but not always enough at the right time. Highly refined petroleum oils, vegetable oils and high-pressure water sprays (with or without soap or surfactants) are among the often used remedies. High pressure water sprays, from a nozzle or heavy overhead rainfall, wash off or injure cochineal scales; and this remedy is sometimes used post-harvest by packing houses to clean fruit prior to shipping. Laboratory studies indicate that epazote (Chenopodium ambrosioides), mint (Mentha spp.) and marigold (Tagetes spp.) extracts applied with emulsifiers are potential organic or environmentally friendly synthetic pesticide alternatives.

At the Entomological Society of America (ESA) annual meeting in Minneapolis I talked with Colorado State University extension entomologist Whitney Cranshaw, whose special spiked shoes for killing white grub beetle larvae beneath the soil surface while walking golf course turf and lawns achieved notoriety in Smithsonian magazine many moons ago. This time he was a lonely entomologist, as out of hundreds of passersby no one was stopping at the poster of graduate student Rachael Sitz reporting on a kermes scale vectoring a bacteria causing drippy blight of red oaks in Colorado. Cranshaw was ecstatic having a customer, and figured I was studying the poster display because the kermes scale was also found in California locales such as San Jose, Mammoth Lakes and Monticello Dam on blue oaks and chinquapin bushes. Actually, I was wondering if this particular kermes scale, which went by the scientific name Allokermes rattani, was related to Old World kermes scales used for centuries by pigment artists in Europe and Asia. According to Cranshaw, workers handling the Colorado kermes scale came away with hands dyed a deep brown. So, perhaps this “pest” scale insect is indeed an untapped resource, similar to cochineal, waiting to be discovered by textile artists, painters and photographers looking for natural organic pigments.

My own interest in these insect pigments is a bit abstract, how to incorporate these pigments into the photographic printing process, inspired in part by viewing Robert Rauschenberg’s vegetable pigment prints with photo images from Indonesia. Cochineal was apparently on occasion used in early color photography printing, dating back to the 1800s and heliochromes, which I surmise are solar prints that also use silver as a light-sensitive pigment. Some modern authors talk of a “green synthesis,” fusing conventional silver nanoparticle photography with cochineal red pigments; but I have not found much on the subject. “Color photography,” U.S. Patent No. 923,019 from 25 May 1909 reads: “To all whom it may concern: Be it known that I, EDGAR CLIFTON, a subject of His Majesty the King of the United Kingdom of Great Britain and Ireland, residing at 3 BeaufortVillas, London Road, Enfield, in the county of Middlesex, England, have invented certain new and useful Improvements in Color Photography…known as the two color process; the three color process; and the four plate process…so that the assemblage gives more or less natural color effects…As the red dye: alizarin (with alumed reliefs), cochineal red (or carmin with ammonia), or magdala red…”

SCALING UP PRODUCTION of pigment scales, versus natural harvest, is often surprisingly difficult. For one thing, about 14,000 individual scale insects are needed to obtain 100 grams of raw cochineal pigment. Far from being dumb savages, ancient Mexico’s New World cochineal growers were superb insect breeders. The best cochineal “breeds” contain 18%-30% pigment by dry weight. Spaniards settling in the New World never mastered the delicate art of cultivating cochineal scale on prickly pear cactus, and instead relied on the indigenous los indios de Mexico, some of whom grew rich on the cochineal trade in what was essentially a free market. Many Spanish colonists found it intolerable that the natives were becoming the richest citizens, and this led to all kinds of frictions and conflicts aimed at turning the natives into poorer, more docile (less uppity) and easier to control colonial subjects. The Spanish were remarkably successful at keeping curious outsiders out of the cochineal production areas for centuries, making the cochineal red dye one of the world’s all-time best kept trade secrets. Most Europeans assumed the grana or granules of cochineal were seeds or plant material, like indigo or madder. On those rare occasions when the secret was revealed, the public refused to believe that cochineal red was literally dried insects. This combination of secrecy and worldwide ignorance allowed the Spanish cochineal monopoly to persist for several centuries and be more lucrative than precious metals.

As any entomology grad student can tell you, the same insect that is an abundant pest can often be impossibly hard to grow when you want it for experiments or as a thesis subject. For one thing, the “insect crop” usually has its own set of pests (called natural enemies), which for cochineal scales includes bacteria, lady beetles, syrphid or hover flies, predatory caterpillars, rodents, reptiles and birds. To prevent “crop failure,” cochineal scales need pampering and protection: 1) from natural enemies; 2) shade to protect from direct sunlight; 3) shelter from heavy rains that wash off and injure the scales. Raising cochineal scales as “farm animals” or “livestock” on prickly pear cactus was often a family enterprise in Old Mexico, an art or skill passed down from generation to generation. The prickly pear cactus itself is still also food, animal fodder and medicine in Mexico. But cochineal grana are no longer treated like money or currency, as it was in Aztec Mexico when cochineal was used in payment of tribute or taxes. In that sense, in contrast to a modern dollar, euro, yen, peso, pound, rupee or digital currency, which cannot be directly used as dyes or medicines, the grana possessed an exquisite versatility and flexibility in ancient times.

CARMINIC ACID, a MEDICINAL CHEMICAL pigment compound extracted from cochineal and first synthesized in 1998, belongs to a class of anti-tumor and antibiotic compounds called anthracycline derivatives, which “are believed to develop their cytotoxic effect by penetrating into the tumor cell nucleus and interacting there with DNA,” write chemists at Gazi University in Ankara, Turkey. Combined with other compounds, cochineal is also active against viruses and other microbes. In Tamil Nadu, India cochineal scale insects collected from cacti are crushed, boiled in water and dried to a powder used against whooping cough and as a sedative. Other traditional uses likely abound.

In nature, cochineal functions as an insect repellent. One theory is that cochineal repels ants, protecting young scale insects before their protective waxy outer covering forms. A carnivorous caterpillar eating the scales incorporates the cochineal dye into its own bodily defenses. A study in the Journal of Polymer Science concluded that cochineal and other natural dyes (madder, walnut, chestnut, fustic, logwood) and mordants (aluminum, chrome, copper, iron, and tin) increased the insect resistance of the wool fabric to attack by black carpet beetles.” Indigo was least effective, and cochineal and madder were most effective except when used with tin and chrome as the mordant or binding agent. I only remember one ESA presentation investigating cochineal as a natural insecticide, and that was back in 2004; the idea was that since carminic acid was already approved as safe for food by the FDA, cochineal could be formulated as an organic bait spray to stop fruit flies without losing organic certification. The researcher theorized that cochineal needs sunlight to be activated as an insecticide, and would thus be ideal for organic agriculture. But as far as I know, the idea was never adapted as an agricultural or quarantine practice.

COMBINING COLOR and HEALING is, however, an idea gaining traction. Carminic acid, a brilliant red compound constituting about 10% of cochineal8, “is one of the most light and heat stable of all the colorants and is more stable than many synthetic food colors,” write Khadijah Kashkar and Heba Mansour in the Department of Fashion Design at King Abdul Aziz University, Saudi Arabia. “Besides the color attributes, recently, also has been reported to beneficial to health with potential antibiotic and antitumor properties. At the beginning of the 21st century it is predicted that many colors will be used for both their additional beneficial functions in the body, as well as, coloring effect.” Whether color and healing were also linked in ancient or Aztec times with cochineal is an intriguing question. Perhaps everything old is indeed new again, but who knows what the ancient New World healers or shaman thought when applying bright red or purple cochineal poultices.

PREVENTIVE MEDICINE might be what to call the combination of organic cotton and natural cochineal dyes to block ultraviolet light from skin contact. Ajoy Sarkar of Colorado State University, writing in the journal BMC dermatology: “The ultraviolet radiation (UVR) band consists of three regions: UV-A (320 to 400 nm), UV-B (290 to 320 nm), and UV-C (200 to 290 nm). UV-C is totally absorbed by the atmosphere and does not reach the earth. UV-A causes little visible reaction on the skin but has been shown to decrease the immunological response of skin cells. UV-B is most responsible for the development of skin cancers…Other than drastically reducing exposure to the sun, the most frequently recommended form of UV protection is the use of sunscreens, hats, and proper selection of clothing. Unfortunately, one cannot hold up a textile material to sunlight and determine how susceptible a textile is to UV rays.” Heavy concentrations of synthetic dyes in synthetic fabrics generally provide good UVR protection, but are not as comfortable as cotton fabrics for warm, humid climates. Generally, the darker the color and the thicker the weave or denser the fabric, the better to protect against UVR. Depending upon the weave (e.g. twill vs sateen), Sarkar reported good to excellent UVR protection with natural dyes such as madder, indigo and cochineal.

COCHINEAL’S 21ST CENTURY RENAISSANCE and resurgence includes harnessing cochineal’s ability to capture (harvest) or route light (photons) and electrons in advanced or next generation optoelectronic devices such as semiconductors, light harvesting antennae, sensors, fuel and solar cells, and molecular information and logic gates for computing devices. I was surprised to learn that natural pigments have a long history in advanced electronics: “As early as the birth stage of lasers, coumarin, which is found naturally in high concentration in the tonka bean (Dipteryx odorata), was used in dye lasers” and “coumarin dye is still the basic active medium for many tunable dye laser sources,” writes M. Maaza (2014) of the University of South Africa. “Extracts from Hibiscus sabdariffa, commonly known as Roselle, carminic acid of the cochineal scale and saffron exhibit exceptional nonlinear optical (NLO) properties of a prime importance in optics.”

THE “NEXT GENERATION” SOLAR CELL replacement for today’s silicon-based solar cells will probably be a dye-sensitized solar cell (DSSC) based on titanium dioxide (TiO2), a semiconductor material that is fused with color pigments analogous to those used in conventional color photography (e.g. silver halide emulsions sensitized by dyes). TiO2 and other metal oxides are widely used in medicine, food preservation, cosmetics, sunscreens, paints, inks and a wide range of electronic devices for sensing, imaging, optics, etc. TiO2 is relatively inexpensive, and deemed low toxicity. Interestingly, TiO2 nanoparticles for solar cells can be produced from cultures of bacterial cells, such as the Lactobacillus sp. found in yogurt or curd, which means an even “greener” solar cell fabrication process.

The scientific roots of the modern solar cell go back to French physicist Edmond Becquel’s discovery of the photovoltaic effect in 1839; and prototype solar cells with efficiencies of 1% or less also date back to the 1800s. Though Albert Einstein explained the photovoltaic effect in 1904, the development of lightweight solar energy cells to power spacecraft in the 1950s. But the DSSC or Grätzel cell is a 1990s’ innovation attributed to Mr. O’Regan and Michael Grätzel. “This new device was based on the use of semiconductor films consisting of nanometer-sized TiO2 particles, together with newly developed charge-transfer dyes,” and had “an astonishing efficiency of more than 7%,” write Agnes Mbonyiryivuze et al. (2015) in the journal Physics and Materials Chemistry.

Next generation DSSCs or photovoltaic cells are currently undergoing a major design transition using natural color pigments like those found in cochineal scale insects. DSSCs with efficiencies in the 10% to 15% range can be manufactured with titanium dioxide (TiO2) nanoparticles bonded on a thin film with a light-sensitive dye utilizing a rare and expensive platinum group heavy metal, ruthenium (Ru; named after Russia). Ruthenium’s relatively high cost and environmental and toxicology concerns are a barrier to commercialization that is spurring the search for substitutes; namely cheaper and more environmentally friendly natural pigment. Companies working “to bring DSSC technology ‘from the lab to the fab’” include “Dyesol, G24i, Sony, Sharp, and Toyota, among others,” write Mbonyiryivuze et al. (2015). “Functional cells sensitized with berry juice can be assembled by children within fifteen minutes, the large choice of colors, the option of transparency and mechanical flexibility, and the parallels to natural photosynthesis all contribute to the widespread fascination. In 2013, the drastic improvement in the performance of DSSC has been made by Professor Michael Grätzel and co-workers at the Swiss Federal Institute of Technology (EPFL). They have developed a state solid version of DSSC called perovskite-sensitized solar cells that is fabricated by a sequential deposition leading to the high performance of the DSSC. This deposition raised their efficiency up to a record 15% without sacrificing stability…this will open a new era…even surpass today’s best thin-film photovoltaic devices.”

“PIGMENTS MAKE NATURE COLORFUL and LIKABLE,” writes Chunxian Chen, a researcher at the University of Florida’s Citrus Research and Education Center and the editor of a 277-page book published by Springer in 2015, Pigments in Fruits and Vegetables: Genomics and Dietetics, which places a heavy emphasis on the nutritional and medicinal benefits of colorful natural pigments like those coloring crops of carrots and sweet potatoes orange and radishes and tomatoes red. “Plant pigments usually refer to four major well-known classes: chlorophylls, carotenoids, flavonoids, and betalains…Chlorophylls are the primary green pigments for photosynthesis. The latter three are complementary nongreen pigments with diverse functions…The importance of colors in living organisms cannot be overstated…they are biosynthesized behind the scenes in living organisms and ultimately ingested in daily diet.” Presumably this daily consumption and medicinal benefits makes natural pigments in general logical and sustainable alternatives to expensive heavy metals in “green” electronic, computer and solar energy cell designs.

Agnes Mbonyiryivuze, in her 2014 dissertation titled “Indigenous natural dyes for Gratzel solar cells: sepia melanin,” provides a readable overview of solar energy cells utilizing natural pigments. The list of natural pigments fabricated into solar cells is long, and the sources range from cochineal scale insects, green algae, baker’s yeast, fungi and bacteria to bougainvillea flowers, Chinese medicinal plants (e.g. tea, pomegranate leaves, wormwood, mulberry fruit) and food crops like beets, parsnip, purple cabbage, blackberry and black grapes. The black pigments are of particular interest, including skin melanins providing UV protection and the black powder from cuttlefish (Sepia officinalis) ink sacks. “To maximize the absorption of more photons from the sun light for DSSC,” writes Mbonyiryivuze, “it is better to have a black dye sensitizer having extremely high broadband absorption. It should absorb not only in visible range but also in ultraviolet and near-infrared regions. This challenge can be handled by using natural dyes from other sources such as fauna from which sepia melanin was obtained. Melanins are well-known natural pigments used for the photoprotective role as a skin protector because of their strong UV absorbance and antioxidant properties. Melanin possesses a broad band absorbance in UV and visible range up to infrared.” Sepia melanin “can also conduct electricity and is thus considered a semiconductor material.”

“There are numerous trials of solar cell construction which are based on biomolecules and supramolecular systems, for instance, chlorophylls, porphyrins, phtalocyanines, and other natural or bioinspired dyes,” write researchers in Poland constructing double layer solar cells with cochineal red and gardenia yellow pigments bonded to TiO2 nano-surfaces. “Hybrid materials incorporating biomolecules immobilized on conducting or semiconducting surfaces are unique systems combining collective properties of solids with structural diversity of molecules, which besides photosensitization show other unique electrochemical and catalytical properties.”

According to Mousavi-Kamazani et al. in Material Letters (2015), quantum dots composed of cochineal and copper offer the economically attractive “possibility of single step production of three-layered solar cells.” Clearly, though the distance might be measured in years or decades, we are getting closer to a cochineal and natural pigment renaissance that transcends traditional fabric dyes and artist’s pigments and extends into medicine and the heart of modern computers, lasers and electronic and optical devices of all sorts.