Venetian plaster can be painted over if the Venetian plaster is less than 5 millimeters thick on the wall. For Venetian plaster that is thicker, painting over the plaster may not provide a smooth finish and may look cheap or have a "stucco" look to it.
Venetian plaster is a term that is used frequently in the home improvement world, but rarely do the people using the term truly know what it means. Venetian plaster is not a faux finish as it is so commonly called and is actually an authentic veneer wall finish. It is natural and lime-based so that once it has been applied, it returns to a natural lime and marble state. This creates actual stone on the wall.
Venetian plaster cannot be bought at most local home improvement stores even though there are products there that will be labeled "Venetian plaster." These products, if a person looks at the ingredient list, are often made out of acrylic polymers and gypsum or clay fillers; they are synthetic Venetian plasters. They might look similar to Venetian plaster, but they are not authentic Venetian plaster. After a short time, they will begin to look like a paint finish rather than a true Venetian plaster finish.