The patina surface for sculpture or copper thermal coloring, also known as patina color, modeled after an antique. That is to use chemical, electrolytic, physical, mechanical, and heat treatment methods. A film, coating, or coating that produces a variety of colors for the sculpture surface. Patina’s method is more, the appellation also different. Often depending on the means of treatment and color source for bronze sculpture. Generally can be divided into coating (including spraying) thermal coloring, chemical coloring, electrolysis coloring, electroless plating, and electroplating coloring, vacuum coloring, vacuum plating gold, gold coloring technology. Among, the most commonly used are chemical coloring, dyeing, heat treatment coloring for bronze sculpture. The traditional coloring methods are many, especially in copper and copper alloy artworks that are more widely used.
1>Pre-patina treatment for copper and copper alloy castings
In order to ensure that the sculpture surface of metal artworks can form a uniform color, good combination, strong corrosion-resistance coloring layer. Before that, the surface of the sculpture must be pretreated with oil removal, erosion and rust removal, polishing, and so on. There are a variety of oil removal methods, which generally can be selected according to the appropriate conditions and the size of the work.
1-1>Wipe and remove oil: use a brush or cloth dipped in detergent, washing powder, lime slurry, magnesium oxide, and other degreasing substances to wipe the oil on the surface of the work. It is mainly used for the deoiling of works of art with large volume, complex shape, and difficult to be processed by other methods.
1-2>Drum oil removal: put the work into the drum of the polishing machine, add appropriate abrasive and oil removal. Suitable for large batch, small size, not easy to deform art casting oil removal.
1-3>Ultrasonic oil removal: it can remove the oil in the fine hole and the hole, and the metal corrosion on the surface of the work is small. Suitable for oil removal of small art castings.
1-4>Sulfuric acid method: Sulfuric acid can remove the oxide and rust on the surface of the work.
1-5> Etching or pickling process(Chemical coloring is the most common sculpture surface decoration method for copper sculpture and copper alloy).
1-5-1> Sulfuric acid method for sculpture surface: Sulfuric acid can remove the oxide scale and rust on the surface of the work.
Firstly, pour water into a large hard glass container. Secondly, sulfuric acid slowly into the water (equivalent to the amount of water). Dissolve the sulfuric acid solution to remove the oxide scale. It must be washed with clean water. The etching time is about 30 seconds. If the production of gold, silver, and other different sculpture artworks, need to prepare different acid. If the same acid solution is used for a long time, the concentration of the liquid will decrease. So the solution must be remodeled frequently. Copper etching can be used to brush the work with a metal brush. Wash dilute sulfuric acid with clean water and dry it.
1-5-2:Preparation of nitric acid solution: the same steps as the production of sulfuric acid solution.
Our handlers can not be rapidly poured and do not let the water directly touch the sulfuric acid. Because sulfuric acid spatters easily cause scalds or spray on the clothes will burn holes in the solution for handlers. It can burn the skin. So, handlers hand sure to use rubber gloves to protect themselves and handle with extra care and can not touch the liquid.