Latte Art

In the United States, latte art was developed in Seattle in the 1980s and 1990s, and particularly popularized by David Schomer. Schomer credits the development of microfoam ("velvet foam" or "milk texturing") to Jack Kelly of Uptown espresso in 1986, and by 1989 the heart pattern was established and a signature at Schomer's Espresso Vivace. The rosette pattern was then developed by Schomer in 1992, recreating the technique based on a photograph he saw from Cafe Mateki in Italy. Schomer subsequently popularized latte art in his course "Caffe Latte Art".
Physics
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.