Silver is often used simply as a precious metal, including currency and decorative items. It has also long been used to confer high monetary value to objects (such as silver coins and investment bars) or make objects symbolic of high social or political rank.[47]
The contrast between the bright white color of silver and other materials makes silver useful to the visual arts. By contrast, fine silver particles form the dense black in photographs and in silverpoint drawings. Silver salts have been used since the Middle Ages to produce a yellow or orange color in stained glass, and more complex decorative color reactions can be produced by incorporating silver metal in blown, kilnformed or torchworked glass.[47]
Currency[edit]
Main articles: Silver coin and Silver standard
Silver, in the form of electrum (a gold–silver alloy), was coined around 700 BC by the Lydians. Later, silver was refined and coined in its pure form. Many nations used silver as the basic unit of monetary value. In the modern world, silver bullion has the ISO currency code XAG. The name of the pound sterling (£) reflects the fact it originally represented the value of one pound Tower weight of sterling silver; the names of other historical currencies, such as the French livre, have similar origins. In some languages, including Sanskrit, Spanish, French, and Hebrew, the word for silver may be used to mean money.
During the 19th century, the bimetallism that prevailed in most countries was undermined by the discovery of large deposits of silver in the Americas; fearing a sharp decrease in the value of silver and inflation of the currency, most states moved to a gold standard by 1900.
The 20th century saw a gradual movement to fiat currency, with most of the world monetary system losing its link to precious metals after the United States dollar came off the gold standard in 1971; the last currency backed by gold was the Swiss franc, which became a pure fiat currency on 1 May 2000; the issues of 1967 and 1969 (for the 5 franc piece) and 1967 (for the others) were the last Swiss coins minted with silver.[48] In the UK the silver standard was reduced from .925 to .500 in 1920. Coins that had been made of silver were changed to cupro-nickel in 1947; existing coins were not withdrawn, but ceased circulating as the silver content came to exceed the face value. In 1964 the United States stopped minting the silver dime and quarter; the last circulating silver coin was the 1970 40% half-dollar.[49] In 1968, Canada minted its last circulating silver coins, the 50% dime and quarter.
For most of the century after the Civil War in the United States, the price of silver was less than the face value of circulating silver coins, reaching its nadir of about $.25 per ounce in 1932,[50] and the silver coins of the United States were effectively fiat coins for much of that history. Not until 1963 did the price of silver rise above the threshold of $1.29 per ounce, at which time the silver content of pre-1965 United States coins was equal in value to the face value of the coins themselves.[51]
Silver coins are still minted by several countries as commemorative or collectible items, not intended for general circulation.
Silver is used as a currency by many individuals, and is legal tender in the US state of Utah.[52] Silver coin and bullion is an investment vehicle used by some people to guard against inflation and devaluation of the currency.
Jewelry and silverware[edit]
Main articles: jewelry and silversmith
Jewelry and silverware are traditionally made from sterling silver (standard silver), an alloy of 92.5% silver with 7.5% copper. In the US, only alloys at least 0.900-fine silver can be sold as "silver" (frequently stamped 900). Sterling silver (stamped 925) is harder than pure silver and has a lower melting point (893 °C) than either pure silver or pure copper.[5] Britannia silver is an alternative, hallmark-quality standard containing 95.8% silver, often used for silver tableware and wrought plate. The patented alloy Argentium sterling silver is formed by the addition of germanium, having improved properties including resistance to firescale.
Sterling silver jewelry is often plated with a thin coat of .999-fine silver to create a shiny finish. This process is called "flashing". Silver jewelry can also be plated with rhodium (for a bright shine) or gold (silver gilt).
Silver is a constituent of almost all colored carat gold alloys and carat gold solders, giving the alloys paler color and greater hardness.[53] White 9-carat gold contains 62.5% silver and 37.5% gold, while 22-carat gold contains a minimum of 91.7% gold and 8.3% silver or copper or other metals.[53]
Historically, the training and guild organization of goldsmiths included silversmiths, and the two crafts remain largely overlapping. Unlike blacksmiths, silversmiths do not shape the metal while it is softened with heat, but work it at room temperature with gentle and carefully placed hammer blows. The essence of silversmithing is to transform a piece of flat metal into a useful object with hammers, stakes, and other simple tools.[54]
While silversmiths specialize and work principally in silver, they also work with other metals, such as gold, copper, steel, and brass, to make jewelry, silverware, armor, vases, and other artistic items. Because silver is so malleable, silversmiths have many choices for working the metal. Historically, silversmiths are usually called goldsmiths and are usually members of the same guild. The western Canadian silversmith tradition does not include guilds but mentoring through colleagues is a common method of professional advancement.[55]
Traditionally, silversmiths mostly made "silverware" (cutlery, tableware, bowls, candlesticks and such). Handmade solid silver tableware is now much less common.
Solar energy[edit]
Solar modules mounted on solar trackers
Silver is used in the manufacture of crystalline solar photovoltaic panels.[56] Silver is also used in plasmonic solar cells. 100 million ounces (685,714.3 pounds (311,034.8 kg)) of silver are projected for use by solar energy in 2015.[57]
Silver is the reflective coating of choice for concentrated solar power reflectors.[58] In 2009, scientists at the National Renewable Energy Laboratory (NREL) and SkyFuel teamed to develop large curved sheets of metal that have the potential to be 30% less expensive than today's best collectors of concentrated solar power by replacing glass mirrors with a silver polymer sheet that has the same performance as the heavy glass, but at much less cost and weight, and much easier to deploy and install. The glossy film uses several layers of polymers, with an inner layer of pure silver.
Air conditioning[edit]
In 2014 researchers invented a mirror-like panel that, when mounted on a building, works as an air conditioner.[59] The mirror is built from several layers of wafer-thin materials. The first layer is silver, the most reflective substance known. Above this are alternating layers of silicon dioxide and hafnium oxide. These layers improve the reflectivity, but also turn the mirror into a thermal radiator.
Water purification[edit]
Silver is used in water purifiers to prevent bacteria and algae from growing in the filters. The silver catalyzes oxygen and sanitizes the water, replacing chlorination. Silver ions are added to water purification systems in hospitals, community water systems, pools and spas, displacing chlorination.[57]
Dentistry[edit]
Previously, silver was alloyed with mercury at room temperature to make amalgams widely used for dental fillings. To make dental amalgam, a mixture of powdered silver and other metals, such as tin and gold, was mixed with mercury to make a stiff paste that could be shaped to fill a drilled cavity. The dental amalgam achieves initial hardness within minutes and sets hard in a few hours.
Photography and electronics[edit]
The use of silver nitrate and silver halides in photography has rapidly declined with the advent of digital technology. From the peak global demand for photographic silver in 1999 (267,000,000 troy ounces or 8304.6 metric tonnes) the market contracted almost 70% by 2013.[60]
Because even when tarnished, silver has superior electrical conductivity, it is used in some electrical and electronic products, notably high quality connectors for RF, VHF, and higher frequencies, particularly in tuned circuits such as cavity filters where conductors cannot be scaled by more than 6%. Printed circuits and RFID antennas are made with silver paints,[5][61] and computer keyboards use silver electrical contacts. Silver cadmium oxide is used in high-voltage contacts because it withstands arcing.
Some manufacturers produce audio connector cables, speaker wires, and power cables with silver conductors, which have a 6% higher conductivity than those of copper with identical dimensions, despite increased cost. Though the issue is debated, many hi-fi enthusiasts believe silver wires improve sound quality.[citation needed]
Small devices, such as hearing aids and watches, commonly use silver oxide batteries because they have long life and a high energy-to-weight ratio. It is also used high-capacity silver-zinc and silver-cadmium batteries.
In World War II during a shortage of copper, silver was borrowed from the United States Treasury for electrical windings by several production facilities, including those of the Manhattan Project; see below under History, WWII.
Glass coatings[edit]
Telescopic mirrors[edit]
Mirrors in almost all reflective telescopes use vacuum aluminium coatings.[62] However thermal or infrared telescopes use silver coated mirrors because it reflects some wavelengths of infrared radiation more effectively than aluminium, and because silver emits very little new thermal radiation (low thermal emissivity) from the mirror material.[63]
Silver, in protected or enhanced coatings, is expected to be the next generation metal coating for reflective telescope mirrors.[64]
Windows[edit]
Using a process called sputtering, silver, along with other optically transparent layers, is applied to glass, creating low emissivity coatings used in high-performance insulated glazing. The amount of silver used per window is small because the silver layer is only 10–15 nanometers thick.[65] However, the amount of silver-coated glass worldwide is hundreds of millions of square meters per year, leading to silver consumption on the order of 10 cubic meters or 100 metric tons/year. Silver color seen in architectural glass and tinted windows on vehicles is produced by sputtered chrome, stainless steel or other alloys.
Silver-coated polyester sheets, used to retrofit windows, are another popular method for reducing window transparency.[57]
Other industrial and commercial applications[edit]
This Yanagisawa A9932J alto saxophone has a solid silver bell and neck with a solid phosphor bronze body. The bell, neck, and key-cups are extensively engraved. It was manufactured in 2008.
Silver and silver alloys are used in some high-quality musical wind instruments.[66] Flutes, in particular, are commonly constructed of silver alloy or silver-plated, both for appearance and for the surface friction properties of silver. Brass instruments, such as trumpets and baritone horns, are commonly plated in silver.[67]
Silver is an ideal catalyst in oxidation reactions; for example, formaldehyde is produced from methanol and air using silver screens or crystallites of a minimum 99.95% silver. Silver (on some suitable support) is probably the only catalyst available today that converts ethylene to ethylene oxide (CH2-O-CH2) in the synthesis of ethylene glycol (used to produce polyesters) and polyethylene terephthalate. It is also used in the Oddy test to detect reduced sulfur compounds and carbonyl sulfides.
Because silver readily absorbs free neutrons, it is commonly added to control rods to regulate the fission chain reaction in pressurized water nuclear reactors, generally in the form of an alloy containing 80% silver, 15% indium, and 5% cadmium.
Silver is used in solder and brazing alloys, and as a thin layer on bearing surfaces, it provides a significant increase in galling resistance, reducing wear under heavy load, particularly against steel.
Biology[edit]
Silver stains are used in biology to increase the contrast and visibility of cells and organelles in microscopy. Camillo Golgi used silver stains to study cells of the nervous system and the Golgi apparatus.[68] Silver stains are used to stain proteins in gel electrophoresis and polyacrylamide gels, either as primary stains or to enhance the visibility and contrast of colloidal gold stain.[69]
Yeasts from Brazilian gold mines bioaccumulate free and complexed silver ions. The fungus Aspergillus niger found growing in a gold mining solution was found to contain cyano metal complexes, such as gold, silver, copper, iron, and zinc. The fungus also plays a role in the solubilization of heavy metal sulfides.[70]
Medicine[edit]
Main article: Medical uses of silver
In medicine, silver is incorporated into wound dressings and used as an antibiotic coating in medical devices. Wound dressings containing silver sulfadiazine or silver nanomaterials are used to treat external infections. Silver is also used in some medical applications, such as urinary catheters (where tentative evidence indicates it reduces catheter-related urinary tract infections) and in endotracheal breathing tubes (where evidence suggests it reduces ventilator-associated pneumonia).[71][72] The silver ion (Ag+
) is bioactive and in sufficient concentration readily kills bacteria in vitro. Silver and silver nanoparticles are used as an antimicrobial in a variety of industrial, healthcare, and domestic applications.[73]
Investing[edit]
Silver coins and bullion are an investment vehicle. Silver investments of various types are available on stock markets, including mining, silver streaming, and silver-backed exchange-traded funds.[74]
Clothing[edit]
Silver inhibits the growth of bacteria and fungi on clothing (such as socks) and is sometimes added to reduce odors and the risk of bacterial and fungal infections. It is incorporated into clothing or shoes either by integrating silver nanoparticles into the polymer from which yarns are made or by coating yarns with silver.[75][76] The loss of silver during washing varies between textile technologies, and the effect on the environment is not yet fully known.[77][78]
