This spring, an exhibit opened at the National Gallery of Art featuring the work of Elizabeth Catlett—a Black artist, activist, and feminist who explored racial and class injustice through striking prints and dynamic sculptures. Her work, as showcased in the exhibition, relied heavily on lithography, a printmaking process in which a design is drawn on stone, treated with gum arabic, and subsequently inked and printed. This artistic process wouldn’t be possible without the acacia tree—namely the species Senegalia senegal and Vachellia seyal—a small, thorny, deciduous tree native to the Arabian Peninsula, Pakistan, west coastal India, and the semidesert regions of Africa.
The acacia tree grows about five to twelve meters tall, with a short trunk and low branches. Its distinctive leaves consist of small leaflets arranged in rows on each side of the central vein, and its small yellow flowers appear in spherical clusters. The tree secretes gum arabic—a tasteless, nontoxic, pale-white or orange-brown sap that may be harvested at the end of the rainy season in sub-Saharan Africa. This globular substance, shaped like a teardrop and unassuming in size, has been used by artists for millennia.
One of the earliest recorded uses of gum arabic was as a binder or thickener in paints. Because gum arabic is both water-soluble and adhesive, it can hold pigment particles together and bond them to surfaces. Around 2000 BCE, the Ancient Egyptians mixed pigments made from ground-up minerals together with gum arabic to create paint, which they applied to papyrus with brushes composed of bundled grasses and reeds.
The gum continued to be used as a paint or ink binder throughout history. Anthropologist and journalist Dorrit van Dalen writes that “[i]n the first century CE, Pliny the Elder noted that writers would use ink made from soot, charcoal and gum.” In the Middle Ages, gum arabic reached Europe by way of pilgrims and merchants traveling to ports of the Levant, the coastal region of the eastern Mediterranean. The ingredient arrived in Christian monasteries, where scribes would dissolve it in water to create ink or paint. These materials would then be used in the copying and illumination of manuscripts.
Colonialism and the Gum Arabic Trade
Arab ports, which fell under Ottoman control after the Ottoman Empire succeeded the Arab caliphate and successor states, dominated the gum arabic trade until the second half of the fifteenth century, when Portuguese maritime explorers made contact with inhabitants of the West African coast. Through interactions with local communities, the explorers learned of an abundant source of gum arabic in the region, purportedly equal in quality to that from the Levant. This discovery shifted the center of gum arabic trade for the European market, laying the foundation for one of the most significant and tumultuous periods in the history of the acacia tree: the eighteenth century.
European demand for gum arabic in the eighteenth century surged to support a growing textile market. When printing textiles, gum arabic played the indispensable role of a thickening agent that helped bind dyes on fabric. Previously used substances, such as starch and flour, failed to achieve the desired level of detail in printed designs. As commercial taste fueled the large-scale production of intricately printed cottons and linens, Europeans’ need for large quantities of gum arabic also rose.
Over the next century, state-run merchant companies—namely the British Royal African Company, the French Compagnie des Indes, and the Dutch West India Company—competed for the control of the trade in Saint-Louis in Senegal, an area where traders met with the local suppliers, the Berbers, to receive gum arabic. While the French sought and achieved a near-monopoly of the trade at Saint-Louis through agreements with the Trarza Berbers, the English and Dutch nevertheless pursued “illegal” trade further north in Portendick, which is in modern-day Mauritania. The struggle between these nations erupted during the Seven Years’ War, in which Britain captured Saint-Louis from the French in 1758, shifting European dominance of the gum trade toward the English. Weakening France’s commercial influence, Britain aimed to establish a monopoly in global trade of gum arabic, even though a treaty signed in Versailles in 1783 returned Saint-Louis and the Senegal River to French control, and French private merchants regained power over the gum trade in West Africa.
Gum arabic’s importance was therefore bound up in political conquest and colonial dominance in West Africa. Historian James L. A. Webb, Jr. describes the prevalence of the gum trade during this period, writing that
In fact, gum arabic emerged as the only natural resource exported in large quantities from West Africa to Europe prior to the abolition of the Atlantic slave trade in the nineteenth century.
Artistic Innovations
As gum arabic entered Europe in increasing quantities during the eighteenth and nineteenth centuries, it fueled artistic production in multiple mediums across the continent. One such medium was watercolor painting, which had existed in varying forms since ancient times but soon reached a new level of prestige in Britain. As Elizabeth E. Barker explains, “The rise of watercolor painting as a serious artistic endeavor progressed hand-in-hand with the improvement and commercial development of its materials.”
Watercolor cakes, invented by William Reeves in 1780, emerged as a pivotal material innovation in the history of watercolor. As recent material analysis demonstrates, gum arabic was predominantly used as a binder in these small and hard cakes of paint. Artists could produce paint with cakes by dipping them in water and then rubbing them on a saucer. Soon after the invention of watercolor cakes, paint manufacturers known as Artists’ Colourmen sold ready-made boxes, which allowed artists to easily venture outdoors for sketching. From the mid-eighteenth to the mid-nineteenth century, Britain entered the so-called “Golden Age of watercolor,” a time when artists elevated the status of the medium and pushed it to new levels of expressive potential in brilliantly colored landscape paintings.
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As watercolor materials incorporated gum arabic, the printing industry would soon also come to rely on the substance. In 1798, German author and actor Alois Senefelder invented a new printing technique that would contribute to the rapid reproduction and circulation of images in the nineteenth century: lithography. The artist or printer drew a design onto a flat stone before fixing the image to the surface with a gum arabic solution. During his experiments, Senefelder noted that gum arabic was a principal component in the preparation of the lithographic stone.
“I had hoped to have been able to dispense with the gum-water,” he wrote, “but was soon convinced that it really enters into chemical affinity with the stone, and stops its pores still more effectually against the fat, and opens them to water.”
Since the drawn image remains greasy while the stone is receptive to water, oil-based ink only prints the design.
Because the lithographic stone experienced minimal wear during printing, a single stone could yield a nearly unlimited number of prints. Furthermore, the printing process, which simply required the artist to draw on stone, was more convenient than the earlier, labor-intensive processes of woodblock print and etching on copperplates and enabled a more varied aesthetic quality in printed images. For these reasons, artists began to fully adopt this new printmaking process by the 1820s, especially in France. Lithography blended artistic and commercial interests, becoming well-suited for magazine illustrations, satirical images, and pictures that could be hung at home.
The invention of lithography shifted European and North American visual culture toward one of mass-produced visual media. Not unlike today, the nineteenth and twentieth centuries saw a flood of commercial, standardized, and reproducible images in billboards, newspapers, stamps, and more. Although gum arabic was an agent of reproduction in this context, it also served a different function in photography.
In the middle of the nineteenth century, photographers frequently experimented with photographic materials and processes. One innovation in the early days of photography became known as the gum dichromate process, in which paper was coated with a light-sensitive emulsion—made up of a mixture of gum arabic, a dichromate salt such as potassium, and a pigment—and exposed to light through a negative image to harden the emulsion. This resulted in high-contrast, grainy, and soft photographs, which allowed artists to push against popular manufactured and standardized photographs in Europe.
Gum’s Enduring Legacy
In the twentieth century, British and French firms continued to exert control over the gum arabic trade until nations in the Sahel region of Africa gained their independence around 1960. Sudan soon emerged as and remains the world’s largest producer of gum arabic, providing around 80 percent of the global supply of the substance. As countries like Sudan independently took charge of the supply of gum arabic, they were met with rising global demand for this commodity and its new commercial applications.
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In the current global economy, gum arabic remains vital across multiple industries. In the food and beverage industry, it’s frequently used to improve the texture of various foods, prevent crystallization in soft drinks, and stop separation in liquids. In the pharmaceutical industry, it’s used in the creation of various vitamins and tablets and improves the consistency of oral medications. And its properties remain unique. Mohammad Zarrag, an exporter of gum arabic, suggests that “[n]o other ingredient can do what gum arabic does. It cannot be replaced by anything else. People have tried but not succeeded.” This sentiment is reflected in explosive industry growth: exports of unprocessed and semi-processed gum have nearly tripled in the last three decades.
Today, both the acacia tree itself and the process for harvesting gum arabic are at risk. The tree faces several threats, including habitat decline due to climate change, livestock grazing, droughts, fires, and overharvesting. Rising temperatures have made harvesting, which is carried out by hand, increasingly dangerous, and the economic viability of the local business rests precariously in political instability. Conservation efforts such as the Great Green Wall Project seek to combat desertification and climate change by planting trees across the Sahel region. Amidst today’s uncertain outlook on gum arabic, mired in threats of climate change and caught between political tumult and the demands of multinational corporations, it is perhaps in the enduring legacy of artworks, like Catlett’s lithographs, where gum arabic continues to steadily tell its story. The Dumbarton Oaks Plant Humanities Initiative seeks to bring these dynamic conversations about plants to the fore.
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