Verdigris is the green rust or patina on copper, created as the metal reacts with oxygen in the environment. Copper corrodes green to blue in varied hues. Verdigris is a collective term for different copper acetate shades.
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The corrosion of copper by air is a coveted look for statues and roofs including the Canadian Parliament Buildings and American Statue of Liberty. The dome of Temppeliaukio Church in Finland is an impressive example of verdigris.
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In a view of the Parliament Buildings, Ottawa Canada, verdigris roofs are visible on several structures. The round building at right with brown roof is the Library of Congress. Its copper roof is recently replaced and has not yet achieved the green patina of the others.
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In Europe the Berlin Cathedral Church (Berliner Dom) and Belvedere Palace, Vienna are famous examples of copper roofs with green patina. As a standardized color verdigris is a pleasant but difficult addition to the palette.
Verdigris patina is never a single color. It actively grows and changes. The natural purpose of verdigris is to create a protective layer over the metal. It prevents further copper degradation.
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Variations of verdigris can be divided into two groups: basic verdigris and neutral or "blue" verdigris. Difference in color is contingent on the hydration level and degrees of basicity, or how it reacts to acids.
Bronze and brass also develop green-blue patinas due to high copper content. Bronze is 88 - 90% copper and 10 - 12% tin. Under natural conditions, copper takes 5 to 30 years to grow mature verdigris. Early pigment makers hasten the process by adding an acid.
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Brass is about 66% copper and 34% zinc, also in various ratios of combination. Either bronze or brass might also contain arsenic or lead. One or both are historically added to copper or copper alloys to strengthen the compound or replace an ingredient such as tin.
Verdigris is a toxin described as mild, with poisoning effects including nausea, anemia - and death. Immunity to low levels of verdigris was found in female workers in Montpelier, France. Copper gives rocks like turquoise and malachite their varied blue to green hues.
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Early verdigris producers create copper acetate by treating copper hydroxide with acetic acid. The historical methods used for producing verdigris are recorded in artistic treaties, manuscripts on alchemy, works in natural history, and texts on medicine.
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The most common ingredients used are copper and vinegar. Another quick way of corroding copper for the verdigris is to pour human, dog or horse urine on the copper. The acids in urine react with the chemical in copper to create the verdigris effect.
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In the Middle Ages (476 - 1450 CE), copper strips are attached to a wooden block with acetic acid. The block is buried in dung. In a few weeks, the block can be unearthed and verdigris scraped off. In pigments, verdigris first appears on the artists' palette c. 1306 CE.
Demand for the product rises, with Montpelier, France, a center of industry in the 18th century CE. Climatic conditions support a prosperous production. Most of the verdigris industry is run by women.
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The method developed in Montpelier evolves in household cellars. Makers put plates of copper in clay pots and fill the pots with distilled wine. The acid of the grape brings forth crystals on the copper. These develop into verdigris to be scraped off when fully grown.
It's a profitable largely home-based business. At least 80% of product is exported through certified female brokers.
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In the early 18th century, the French government enforces inspection systems, ostensibly to address fraudulent practices. By the 20th century, production of verdigris moves on to other centers.
Used as pigment since antiquity, verdigris is found in paintings in Rome and Pompeii. As artists' pigment it's popular in the Middle Ages, Renaissance and Baroque periods.
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Beloved for its transparency and brilliance, it's a favorite of artists such as Raphael and Botticelli. Its height of artistic use is in the 15th and 16th centuries. However, the color is very unstable.
The artists don't know the long-term effects of verdigris in painting. Over time the pigment continues to corrode and change color. Centuries later, the bright blue-greens used by the artists decay into darker more dismal tones, as seen in the robes and angel's wings below.
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At the time of the painting it's hard to get strong greens from the pigments available. Renaissance painters seek dynamic brilliant color. Black and yellow make natural greens, blue and yellow create more intense tones.
Orpiment produces vivid yellow but as an arsenic sulfide mineral is also toxic. Prussian blue, a brilliant cyanide compound, hasn't yet been invented. It hits the shelves at the beginning of the 18th century.
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Bernardinus Ramazzini, 18th century doctor from Italy, is the first to suggest illness affecting artists and workers may be lead or pigment poisoning. In his De Morbis Artificum Diatriba he writes,
“Of the many painters I have known, almost all I found unhealthy … If we search for the cause of the cachectic and colorless appearance of the painters, as well as the melancholy feelings that they are so often victims of, we should look no further than the harmful nature of the pigments…”
In early Italian, Netherlandish, and German paintings, verdigris yields pure green tones for landscapes and drapery. Verdigris is also used as a glaze. When verdigris glaze is combined with lead white or lead-tin yellow, it creates a strong saturated green.
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It's in demand as oil-based house paint for French and Dutch country homes. Verdigris is also an ingredient in a type of imitation Chinese varnish on European lacquer ware.
Use of verdigris declines in the 19th century. New colors appear in the painterly palette, such as viridian. A chromium oxide, viridian has such side effects as respiratory inflammation, lung irritation and chronic skin ulcers.
Another 19th century green embraced by artists is Emerald Green, an enchanting name with a poisonous secret. The color recipe is fiercely guarded. Among other ingredients it's packed with copper and lead.
Like many poisons, toxins and venoms, verdigris is used as medicine. Copper itself appears as a treatment in an Egyptian medical text c. 2600 BCE. The text records use of copper to sterilize chest wounds and drinking water.
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Copper does work to purify water is it's naturally antibacterial and antifungal. In early times, people threw coins of copper or silver into ponds, wells, or other sources of water, which are considered sacred. The person asks a favor or blessing from the spirit of the wishing well.
The Ebers Papyrus of Egypt (c. 1500 BCE) prescribes copper compounds for headaches, trembling of limbs, burn wounds, itching and growths in the neck, such as infections, tumors or boils.
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Greek physician Hippocrates recommends verdigris to treat leg ulcers caused by varicose veins. In the 18th century it's applied to heal canker sores on the mouth. Verdigris or copper sulfate are also used to treat eye ailments such as bloodshot or inflamed eyes, or cataracts.
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