Gum arabic is one of the most versatile materials in art, serving as the primary binder in watercolor paint, a key chemical agent in lithographic printmaking, a light-sensitive medium in historical photography, and a flow controller in calligraphy inks. It comes from the hardened sap of acacia trees, mainly species grown in the Sahel region of Africa, and its unique water-soluble properties make it useful across a surprising range of artistic disciplines.
The Binder That Makes Watercolor Work
Gum arabic’s most well-known role in art is as the binder in watercolor paint. Watercolor is essentially a suspension of pigment particles in a solution of water, gum arabic, and a small amount of surfactant. The gum surrounds individual pigment particles and holds them in suspension while the paint is wet, then adheres them to the paper once the water evaporates. Unlike oil paint binders, gum arabic remains water-soluble after drying, which is why you can reactivate dried watercolor with a wet brush.
Beyond holding pigment in place, gum arabic influences how watercolor looks and handles. Adding extra gum arabic to your paint increases gloss, transparency, and flow without dulling the intensity of deep colors like Prussian blue. Some artists mix a small amount of gum arabic solution directly into their palette to push a wash toward a more luminous, glaze-like finish.
Making Your Own Watercolor Paint
Artists who grind their own watercolors start with a gum arabic solution, then mix in dry pigment until the consistency feels right. The ratio varies by pigment because some powders absorb more binder than others. A simple test: let a painted swatch dry completely, then wipe your finger across it. If pigment stays put on the paper, you’ve added enough binder. If it smears or lifts, you need more gum arabic.
Gum arabic on its own is brittle when dry, which is why most watercolor recipes include a plasticizer. Honey and glycerin are the two most common additions. Honey is a humectant, meaning it draws moisture from the air, which helps dried paint rewet more easily. It also acts as a plasticizer, increasing the flexibility of the dried gum and preventing cracking in paint pans. Glycerin does essentially the same thing and works as a vegan alternative. Many artists use both: a couple of tablespoons of honey in the binder medium, plus a small amount of glycerin (around 24 drops) to further improve flow and vibrancy. Too much honey alone can leave the paint sticky.
Lithographic Printmaking
In lithography, gum arabic plays a completely different role. Rather than binding pigment, it acts as a chemical agent that controls where ink sticks to a printing surface. Lithography works on the principle that grease and water repel each other. An artist draws on a flat limestone slab or metal plate with a greasy crayon or ink, then treats the entire surface with a solution of gum arabic and a small amount of nitric acid. This “etch” desensitizes the non-image areas, making them attract water and repel the greasy printing ink. The drawn areas, meanwhile, continue to accept ink.
After the initial etch, the artist applies a thin layer of pure gum arabic across the whole stone to even out the surface chemistry before inking. This step stabilizes the print, ensuring clean separation between the image and the blank areas through repeated print runs. Without gum arabic, lithography as a medium simply wouldn’t function.
Gum Bichromate Photography
One of the more unusual uses of gum arabic is in gum bichromate printing, a photographic process dating to the 19th century that artists still practice today for its painterly, handmade quality. The process exploits a chemical reaction between gum arabic and a dichromate salt that becomes sensitive to light.
Here’s how it works. The gum arabic molecule is a flexible chain of hydrogen and carbon atoms with oxygen branches along its length. When mixed with a dichromate salt and exposed to ultraviolet light, the dichromate releases oxygen atoms that fill gaps between those branches, stiffening the chain. The stiffened gum becomes insoluble in water. More light exposure means more stiffening. The artist coats paper with a mixture of gum arabic, dichromate, and pigment, exposes it under a photographic negative, then washes the print in water. Areas that received the most light harden and trap pigment in their porous structure. Unexposed areas dissolve away, along with any remaining dichromate. The result is a print with soft, organic tones that can be layered in multiple colors through repeated coatings and exposures.
Calligraphy and Ink Making
Calligraphers have used gum arabic for decades as a viscosity adjuster in ink. Its molecular structure forms hydrogen bonds with water and pigment particles, thickening the ink and reducing surface tension. This slows how quickly ink absorbs into paper, giving the calligrapher more control over line quality and reducing feathering, the unwanted spread of ink along paper fibers.
The concentration matters. At lower concentrations (5 to 10 percent by weight), gum arabic provides moderate thickening suited to fine-line work on lightly sized paper. At 15 to 20 percent, it slows absorption enough for brush lettering on medium-weight papers like washi, though it can increase drying time by 40 to 60 percent and create slight drag with broad-edged nibs. At 25 to 30 percent, it creates a temporary barrier film on highly absorbent papers like mulberry, offering maximum feathering control. But at that concentration, it risks crystallizing on the nib and requires careful temperature control during mixing. Calligraphers typically find their sweet spot through experimentation based on their tools, paper, and style.
Two Grades From Two Trees
Not all gum arabic is the same. The two main botanical sources are Acacia senegal and Acacia seyal, and their molecular differences affect performance. Acacia senegal gum has a more highly branched molecular structure (about 78 percent branching compared to 59 percent in seyal) and nearly twice the protein content (1.8 percent versus 0.9 percent). It also produces a more viscous solution because its molecules are less compact and spread out more in water.
Acacia seyal gum, by contrast, has larger but more compact molecules that result in lower viscosity. For artists, this translates to practical differences in how the gum handles when mixed with pigments or applied to a lithographic stone. Acacia senegal is generally considered the higher grade for art use because its greater viscosity and branching give it stronger binding and film-forming properties. Art supply manufacturers typically use senegal-type gum in professional watercolor paints, though many products don’t specify the source on the label.
Glazing and Mixed Media
Outside of these primary applications, artists use gum arabic as a standalone medium for glazing effects. A thin wash of diluted gum arabic over a finished watercolor area adds a subtle gloss and deepens transparency, similar to how varnish works in oil painting but fully reversible with water. Some mixed media artists also use it as a fixative for soft pastel or chalk work on paper, or as a sizing agent to seal porous surfaces before applying water-based media.
Its water solubility is both a strength and a limitation. It makes gum arabic forgiving and easy to work with, since mistakes can be lifted or reworked. But it also means finished works remain vulnerable to moisture unless framed behind glass, which is standard practice for watercolors and works on paper regardless of the binder used.