What is Patina?
Commonly pronounced in the US as pa tee'ne, or puh tee'nuh".
Tree Blue
Most broadly defined as the observed and physical change in a surface over time caused by exposure to oxygen or other environmental elements and compounds. On metal, it is the film of corrosion on the surface caused primarily by the reaction of the metal with oxygen. To put it in perspective, think of an old penny, a rusty pipe, or the Statue of Liberty. However, there is more to it; The natural rate of change depends upon the aggressiveness of the environment. Since the level of pollutants, rainfall, and acidity vary locally, the rate, chemical make-up, and therefore the color and depth of the patina will also vary. Rates of patina build-up and color will change year-to-year, and even seasonally.
Patina is not confined to metal. It can also refer to the change over time in wood or the long-term change in furniture or other items, caused not only by oxidation, but also by repeated cleaning, rubbing and polishing. To summarize, patina is the rich and often lustrous natural toning once only available by waiting months, decades, or eons. Because of the time factor, surfaces with a fine patina often command a premium price.
For metal coating companies, copper, bronze and brass are among the most popular coatings. These have some similarities in the way they naturally patina. Although other elements can be included in the mix, Bronze and Brass are primarily alloys of Copper along with Tin and Zinc, respectively. The natural coating that develops on these copper-based metals can range from brown to green, all in a multitude of shades and hues, depending on time and environment. The desirable green shades (formations of copper carbonate) used to be called Verdigris, but in modern times are usually shortened to Verde or Verdi.
The layer of patina, interestingly, can protect against continuing corrosion and is encouraged to provide a protective barrier against further deterioration. However, this is less likely to be the case in larger cities or areas with higher levels of natural or industrial pollution. In these cases, the green and blue colors are mainly from copper sulfides and are not protective, allowing corrosion to wreck the havoc of deterioration beneath the surface. Areas of harmful or beneficial patina can flake-off allowing the patina process begins anew on that area. This phenomenon can be responsible (along with pigeon poop) for some of the wilder patinas seen in many ancient cities.
While we have been reviewing copper and copper alloys, common rust in all it's splendid coloring, is a patina effect on iron and iron alloys such a steel. Rust is Iron Oxide formed by the reaction of Iron and oxygen in the presence of water or atmospheric water vapor. We think rust is beautiful!! Unknown to many, even Aluminum forms a surface oxidation (patina) of Aluminum Oxide almost immediately. It often goes unnoticed because it is, most commonly, in a whitish crystalline form. Like the patina on copper and copper alloys, the surface oxidation on Aluminum protects the metal against further deterioration.
We look forward to the way metal ages over time, but waiting years for this weathering process is not always the most practical way to enjoy the coloration changes. Patination is the art of applying coloration to metals. It can be done to add a sense of mood and drama to an object, to enhance and highlight detail or to accelerate the ageing process. The patinator can utilize compounds to hasten the natural process or can add other patina colors such as blue, red, or black. Artists have been using patina since, least the 1800s. Sculptor, Auguste Rodin used patinas on many of his bronze pieces. Likewise American Western Artist Frederick Remington, used patinas on his 22 famous statues depicting Cowboy and Western American life.
Metal coating companies primarily apply patinas to add the interest of shading that would be acquired with some measure of time. While a shiny new penny may a fun thing to receive, it is rather too coppery and of such a monotone color that the detail gets lost in the evenness of the luster. Contrast that new penny with one that has been in circulation for years and you will notice that the high spots have been polished or rubbed shiny from use, and the low relief areas remain darker. Overall, a much nicer presentation that allows you to see greater detail.
Patina may be applied to cleaned metal, either hot or cold. Heat from a torch is often used to speed the oxidation process on sculpture and sheet goods. For cold-spray metal coatings patinators use the cold process, which is safer and keeps fumes to a minimum. Most prefer the ease and consistency of store bought over home-brew, but they are expensive considering the Hazardous Materials shipping cost. At times, patination recipes have been garnered from sources online or from books on the subject. Most chemicals can easily be purchased, but you might have to show ID and sign for some of them due to National Security Concerns. Try your local art store, chemical supply company, school supply house, or even your local drug store.
For sign-makers, patination chemicals reach the signs and plaques via several methods. Patinas can be sprayed, brushed, or rubbed onto the metal-coated piece. As an alternative, size allowing, small pieces are sometimes dipped into a vat of patina chemicals. This colors the entire piece. The high areas are then polished to specifications removing some or all of the patina, thus leaving the relief areas in a very natural patinated state.
Very few of us actually see bronze, brass, or copper right out the mold, and just polished. You might be shocked to see, that like a new penny, it just does not look right without a little oxidation, which is, of course, Patina.
How to Patina Metal
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