Latte Art

Latte art is a mixture of two colloids: the crema, which is an emulsion (liquid-in-liquid) of coffee oil and brewed coffee (water); and the microfoam, which is a foam (air-in-liquid) of air in milk. (Milk itself is an emulsion of butterfat in water, while coffee is a solution of coffee solids in water.) Neither of these colloids are stable - crema dissipates from espresso, while microfoam separates into drier foam and (liquid) milk - both degrading significantly on the order of minutes, and thus latte art lasts only briefly.
Technique
Latte art requires first producing espresso with crema and microfoam, and then combining these to make latte art.