Venetian Plasters
While traveling in Italy, I discovered Italian plaster finishes, called “decorative
stucco” by the Italians. This plaster is remarkably glossy and—considering it was mid-July—surprisingly cool to the touch. It
piqued my interest because of my own business experience with painting. Throughout the remainder of my travel, I came across
various plasters and finishes at urban historical buildings, churches, villas, and museums. I even had the opportunity to learn
more about these plasters in conversations with plaster craftsmen.
Back in the U.S., after months of researching Venetian plasters , I formally began studying the techniques of applying Venetian plasters.
The process of creating Venetian plaster starts with a cool, white piece of limestone (calcium carbonate), and interestingly, this is finished product as well. The limestone is first burned in a kiln at temperatures between 900°C and 1200°C. Carbon dioxide is released into the air, leaving a product called “quicklime.” In the next process called “slaking,” water is introduced to the quicklime to create a hydrate: calcium hydroxide. Time is an important factor in slaking; in Italy, a quality plaster company will slake a plaster for at least a year and up to three years.
The resulting hydrate can be either wet or dry, depending on how much water is used. With enough water to create putty, Italians call this grassello, pigments and aggregates such as fine marble dust can then be included to yield a distinctive texture and appearance. After the plaster is applied to a wall surface, carbonation takes place. The plaster takes in carbon dioxide from the air for approximately twenty-eight days and finally reverts to its original—now enhanced—form, limestone.
