Nickel silver

Nickel Silver is a copper, nickel, and zinc alloy that contains nearly 30% nickel. Nickel Silver contains no actual silver but is named for its silver-white appearance. In the past, it was also called German Silver and Liberty Silver which led to its present misleading name. It acts like silver because it has an ability to take high amounts of polish.

History
Nickel Silver was first used by the Chinese over 200 years ago. They cast the metal into triangular rings and transported them to Canton where zinc was added. It was originally discovered in 1694 by Hiarni, who named it false nickel or copper nickel. Large quantities of this red, fume-emitting ore resembled copper but did not produce it. When smelted, it produced something that could not be hammered and was extremely brittle. The miners assumed they could not do anything with this product and attempts to use it soon fell by the waste side. In 1751, Aksel Frederik Cronstedt discovered the nickel in these products. In 1824, German brothers by the name of Henninger produced and marketed “new silver”. In 1830, new silver was exported to England where it was called German Silver, until the name was changed (after World War I) to nickel silver. In the early 19th century, the United States imported nickel silver. In the 1830s, nickel silver superseded copper as the metal being combined with silver for metal plating.

Metallurgy
In the beginning, regardless of which country’s method was used, three distinct metals were melted under charcoal or coke dust. Nickel produces a gas when melted and tends to make this process difficult because there are little to no holes for the air to escape. The charcoal and coke dust acted as a blanket and a deoxidizing flux that kept the mixture from getting porous. Nickel Silver is created in roughly the same manner, essentially unchanged. Copper is usually melted first, followed by the nickel. If other metals are added, they are usually charged with zinc first then mixed with the copper and nickel. The metals are then heated, deoxidized and then poured into a mold. Bright white is usually the only Nickel Silver produced by manufactures today but they can be found in shades of green, yellow, pink and blue. In order to achieve a bright white color, the mixture must contain at least 20% nickel and only moderate amounts of zinc. Nickel silver is generally corrosion resistant, nonmagnetic, and strong but ductile. The higher the copper percentage, the less likely it is to sustain trace amounts of corrosion. With its strong but ductile traits, its bright white color, and its propensity to be highly lustrous, Nickel Silver is popular in an array of products, including architectural hardware and ornamental metalwork.

Uses and Installation
Nickel silver is an incredibly diverse metal and was capable of being used for nearly anything. The most popular use for nickel silver was for commercial application until 1914, where it seemed to explode in popularity over night. Nickel silver was being used for jewelry, cigarette cases, hub caps, soda fountains and so much more. It was used architecturally for decorative panels, grilles, railings, plumbing fixtures, and sometimes as trim. It was most popular in Art Deco motifs, being used to separate different colors in the flooring. In the 1930s, it was a favorite for interior and exteriors of buildings. Different shades of nickel were used to relate to other building materials. The Squibb Building in New York has light pink nickel silver in the lobby to complement the stone veneer. Nickel silver remained popular well in the 1940s the ideal material for trim and hardware but nearly died out in the mid 1950s. World War II caused the nickel and copper to be diverted to the war effort. Stainless steel and aluminum had a stronghold following the war because of their inexpensive cost and similar bright white finish. Nickel silver is still used today but predominately for industrial and electrical purposes.

Conservation
Nickel silver is a durable metal that is corrosion resistant. It is attractive and highly popular. Nickel silver can be damaged by chemical pollutants and mechanical strain, both of which have no real treatment. There are no known treatments that specifically address nickel silver deterioration. Polishing nickel silver is one of the only ways that is thought to prevent some problems but does not offer any increase in the nickel silver’s physical strength nor will it protect against chemical pollutants.

Identification
visual examination,spot testing,density
 * Simple methods

xrf,xrd,pixe,libs,electrochemical techniques,metallography
 * Scientific methods

Deterioration
Nickel silver alloys are usually quite resistant to atmospheric corrosion and many mineral and organic acids. In the presence of sulfur, they will slowly tarnish because of the zinc in the nickel silver. Nickel silver, like most nonferrous metals, forms a protective oxide on the top when it comes into contact with oxygen. Without upkeep, the oxide becomes tightly compacted, forming a patina. The patina on nickel silver is usually brownish green and should protect the alloy against further corrosion and surface damage. Nickel silver may also be susceptible to cracking which occurs when it is in a corrosive environment. Temperature, metal composition, and metal structure can also cause tensile stress corrosion cracks. Nickel silver is generally a strong, hard alloy and is abrasion resistant (causing it to become a popular choice for doorknobs and push plates).

Conservation Techniques - architecture
Nickel silver, with a high content of copper, has several of the characteristics found in bronze and brass. Cleaning nickel silver is similar to cleaning bronze or brass. Indoor nickel silver products require little maintenance. Using a non-ionic detergent and a de-ionized water are usually all that is required for cleaning. Natural-fiber bristle brushes are used to scrub off loose dirt and grease and oil are easily cleaned with an a chemical compound such as ammonia with whiting and water. Built-up corrosion and debris may require  a low-pressure washing, which usually includes water or a mineral based lubricant. Also, low grit sandpaper or plastic abrasive pads are usually effective in removing build up. Organic solvents prove most useful in removing graffiti and discolored coatings. Once the nickel silver is cleaned, it should be washed thoroughly with de-ionized water and a protective lacquer or other finish should be applied. Lanolin-based and oil coatings are not recommended, neither is wax due to the high copper content. Since coatings are not permanent, they should be cleaned and maintained on a regular basis.

Cleaning

 * Mechanical removal of corrosion products
 * Chemical removal of corrosion products

Mixture of organic acids

47,5 gms citric acid

47,5 gms sodium gluconate

4,9 gms tartaric acid

1 lit water

Immerse objects in cold or  hot(80C) solution,after treatment  rinse  well and repeat if needs.


 * Electrochemical removal of corrosion products

6 gms sodium carbonate

6 gms sodium  phosphate

1 lit water

up to 12 v,1 A/dm2,stainless steel anode

Object must be connected to negative terminal of current source ,and immersed in solution,anode must be immersed before. Rinse well!


 * Ultrasonic removal of corrosion products

Alkaline cleaner

4-6 gms sodium carbonate

6-8 gms trisodium phosphate

10-12 gms sodium silicate

1 lit distilled water

2-5 minutes,then rinse well and repeat in  needs.


 * Laser removal of corrosion products

Protective coatings
Paraloid B 72 / Paraloid B 67 / Paraloid B 44 / Paraloid B 48 N / Incralac Renaissance Wax / Cosmolloid 80 H basecoat Paraloid B 72 + topcoat Renaissance Wax etc.
 * Clearcoats
 * Waxes
 * Combinations

Replacement
Most companies today produce only the silver white color of nickel silver and yellowish hue of white. Custom orders are usually possible but are expected to be slightly more expensive. The company should be capable of matching the color of the nickel silver as well as its finish.