Applying Venetian Plaster is time consuming and a bit labor intensive but, the finish is awsome.
First, start with a metal trowel (about 6" wide). Round off the edges so as not to gouge into the plaster. Spread your first coat using short strokes. Spread as smooth as possible. You will have gaps. Don't work too big an area at once. Wait approximately 4 hours and apply the second coat. Cover the gaps with the same technique. Remember: as smooth as possible. Wait another 4 hours. The waiting depends on the temperature and humidity. You can now "burnish" the finish. This is where you use the same trowel to basically "friction-burn" the finish to acheive the desired finish.
-Make sure the trowel is constantly clean and free of any burrs.
-Hold the trowel at flat angle pressing on the blade while you burnish in a circular motion.
-WATCH THE GOUGING...Make sure the corners are rounded or ground.