If someone asked you to explain precisely in one sentence, “What is paint?”, how would you answer? You might fall back on a description that encompasses house paints and utility enamel as well as artist’s colors. It would be true to say that paint is “a combination of a colorant in the form of a pigment and a vehicle containing a binder, that forms a durable film over a substrate”. But, that doesn’t explain the ways that artists use paint. It also doesn’t sort out the nuanced differences between similar materials that are used like paint, but called something else.
These boundaries are blurred because artists use many different materials in a huge range of techniques, always pushing the limits. Fundamentally, however, there are properties that most would agree which distinguish paint from something else:
Paint imparts color through pigments:
The ingredient that gives paint its hue is pigment, colorful, solid particles dispersed throughout the vehicle. Pigment holds its color and doesn’t dissolve into the vehicle or migrate once the binder has dried. Dyes are also sources of color for art materials like inks and stains, but in order for a dye to be used in paint, it has to be made into what’s called a “lake pigment” by fixing it to an inert solid.
Paint uses a binder:
Pigment needs a binder to give it adhesive power and to form a film. A paint binder also surrounds the pigment particles and enhances appearance.
Paint has a vehicle:
The paint vehicle is a substance that carries pigment and binder to the substrate. A vehicle can either be a mix of binder and other materials, or vehicle and binder can be the same thing, like the oil in oil paint which is both vehicle and binder in one. By comparison, the vehicle for acrylic paint is an acrylic dispersion base, which has acrylic microparticles, water, dispersants, glycols, and many other components. A paint vehicle, sometimes called a “base”, spreads and flows, and contributes to paint body, workability, and other physical characteristics. When paint is made, pigment is combined with the vehicle in a way that breaks up clusters and clumps so each particle is separately surrounded, in a process called “dispersal”.
Paint forms a covering film:
Even when paint sinks into the support, it still forms a coherent layer. Paint forms a continuous film, held together internally and stuck to the substrate by the binder. A paint film should last as long as the application requires. It should achieve a stable state that doesn’t deteriorate prematurely so that the artist’s expressive work is protected and preserved.
Where it gets complicated:
Some art materials share one or more properties of paint, but we don’t call them paint. Inks, for instance, may have pigments, but they can also have staining dyes that dissolve into the vehicle. Inks may have binders, but the function is different. Drawing inks generally rely on a porous, absorbent support like paper to hold together broad applications. While it’s not necessarily important or desirable for an ink to form a coherent film, a small amount of binder may be present to make it waterproof and keep it from reactivating. Printing inks are extremely similar to paint, but they aren’t formulated for direct application, and they can’t form a thick, durable film on supports.
There is also a lot of variation in painting technique, with many methods of application. Watercolor technique is arguably closer to how ink is applied than it is to the way oils and acrylics are used. Both watercolor and ink are applied thinly on an absorbent paper that holds the medium in a fiber structure, rather than in a continuous, thick film. Watercolors also have “staining pigments” which, while they don’t actually dissolve into the vehicle like dyes, do have a similar behavior because of small particle size.
The lesson we can take from these exceptions and “gray areas” is that how the artist uses a material has a lot to do with whether it can be called “paint”. Even the technique of working with friable soft pastel is called “painting”, despite being a dry, powdery medium. If an ink is mixed with a binder like acrylic medium, for instance, or if acrylic gesso is mixed with tube colors on a palette, it’s hard to interpret those as anything other than paint, despite what the product label says. The spirit of experimentation and joy of combining materials in novel ways has been a part of the craft of painting from the very beginning, and that continues to drive developments in art materials today.