If you search popular DIY websites for Venetian Plaster, you're likely to find statements like this, from the website ehow.com: "Venetian plaster is a faux finish technique for house painting, where the wall surface is painted using a trowel and a thick paint material called venetian plaster."
Don't be mislead. In the same way the term "Burgundy," a term once reserved for the finest red wine from Bourgogne, France, became bastardized in order to market lesser quality wines on the basis of their deep red color, the term "Venetian Plaster" became marketed over the past 20 years in America, to generically refer to virtually any troweled-on, shiny, decorative finish.
These paint-based products labeled "Venetian Plaster" found at large building supply chain stores or paint stores, are synthetics. Many contain dangerous chemicals (read the warning labels) and their application/finishing process can create a toxic interior environment. While these formulations may contain some of the same materials you'll find in true Venetian plaster, they also include vinyl polymers, acrylics, cement, and other chemicals or fillers. Their finished effect feels like plastic or vinyl, NOT the cool, exquisitely polished marble sensation achieved only through real Venetian plaster.
Nor is Venetian Plaster a tinted joint compound, tinted gypsum plaster or tinted portland plaster. Real Venetian plaster is not dry mixed, rolled on or sanded between coats. These faux plasters will not age as gracefully as true Italian plasters, do not have the durability and breathability of natural lime plaster, and as they eventually fade and look dingy and tired, do not impart the same lifetime value as true Venetian plaster.
Authentic Venetian Plaster is distinguished by the natural, organic plaster material itself, and by the special techniques used to achieve the desired effect, which can range from a marble-like translucence, to a rustic, aged stone effect. The techniques are centuries-old, creating a sensuality of multi-dimensional texture, movement and life that is impossible to duplicate with faux products. The surfaces feel organic; the colorations natural and exquisite. Touch the natural Italian plasters, and your fingers will discern the difference.
The finest venetian plasters are imported from Italy, where the natural limestone is the purest in the world. The premium manufacturers of Northern Italy mine a calcium limestone that is slaked and given time to mature, creating a high-grade plaster material suitable for frescos, as well as walls, ceilings and surface decoration. Other grades of lime, called hydraulic limes, are not good for slaking and do not provide the same degree of polish in the finished application. Many have tried to match or copy this product, but like any good cook will tell you, food always tastes better when using the fresh ingredients from the very region that inspired it.
The process is "low-tech" and time-intensive: the lime is soaked in water for a minimum of three years (usually much longer), and like wine in a cellar, left to age in a cool, dark spot. The lime that melts into the water is called grassello di calce or slaked lime, and the top part--the "cream"--is what is used in the Venetian plaster process. Aged, slaked lime brings out the crystallized and reflective characteristics of limestone. The addition of crushed marble, terra cotta or other natural stone to various formulations adds additional sparkle and interest. Special lime plaster pigments are blended into the plasters on site at the time of application, imparting the highest quality, fade-resistant, all natural colors. The color permeates and is embedded into the plaster and not simply applied on the surface.
As the plaster is trowel onto a surface, its moisture content, the angle and pressure of the trowel, and the chemical reaction of exposing the material to air, are all factors in achieving the desired outcome. Mastering the techniques to control the outcome, when using all natural materials, takes training and practice. The result is a natural stone veneer surface with the look of marble, but without the weight. The plaster and the technique can range from a flat matte finish all the way up to a reflective gloss, and can be enhanced with natural, breathable waxes that can be polished to an even higher luster, and add an additional layer of protection in high traffic areas. The fact that the plasters do harden back into stone is what gives the authentic finish its special properties that create a more healthy, organic living environment. The plastered surfaces age gracefully over the years and need little to no maintenance. They are considered a lifetime finish that will never need to be redone.
Compared to decorative painters and faux finishers, the numbers of artisans trained to apply authentic Italian plasters are relatively few, and the best are highly sought after. When you chose the best, you can rest assured that every project is a one of a kind work of art.