Patina is a chemical treatment that converts the copper content in the bronze to various metal salts. In the beginning, a patina was formed naturally from chemicals in the atmosphere or from ground contact. Now we "force" patinas using heat and chemicals. Here is a link to my small monograph on patina work. Click Here Patination is both an art and a science. I used a sulphurated potash base followed by ferric nitrate washes. This is a "standard" outdoor patina. The final finish is a wax formulation I use that was developed long ago and slightly modified by myself. It is applied to a hot surface. It will seal the piece from the elements for a few years. All bronzes require periodic cleaning and rewaxing.
A shot of the final piece in the foundry. The base is limestone, turned by Heritage Stone Works. The total height is 8 1/2 feet. Total time to complete was around 8 to 9 months. I quit counting after 6 months.