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Friday, 12 June 2015 17:28

Jewellery Metals

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Introduction

Visitors to our website Bulrush are often ask about the metals used in the jewelry we offer. As we offer fine jewelry created in gold and platinum; designer jewelry that includes silver and fashion jewelry that’s created in a mixed alloy of pewter and zinc, it is useful to understand the characteristics of each metal, in terms of its use in jewelry, it color, composition and value. This article discusses the characteristics of gold, platinum and silver. For information regarding the metals and care for fashion (costume) jewelry. Please see the article on the Danon Jewellery making process.

 

Precious Metals

We classify precious metals used in the creation of fine jewelry and designer jewelry as including Gold, Platinum and Silver.

 

The characteristics of Gold 

The most commonly sort after precious metal Gold, has been used in the creation of jewelry and as a universal trading commodity throughout history, with an amazing ability to maintain and even increase in value.

  

 

 

 

It’s allure and value is rooted in its very nature and physical characteristics.  Besides its natural color and luster it has a beauty, density, malleability,  and stability unlike any other metal known to man. It is understandable why we find it so attractive. For the creation of precious jewelry its value lies in its natural beauty and resistance to the elements, neither corroding nor changing color over time.  It also maintains its value and even appreciates, especially in times of economic unrest and political instability.

With a chemical element symbol of Au, it is scarce being sought in its natural form as nuggets or grains in rocks, veins and in alluvial deposits.

 

Due to its unique characteristics , it is used for both monetary, jewelry and other industries such as dentistry and electronics. As it is so pliable and malleable, gold can be beaten into very thin sheets and still maintain its integrity i.e Gold leaf. There are many types of jewelry that are created with a non precious metal core and cover in an exterior our shell of gold leaf. It can easily be mixed with other alloys, modifying its purity and hardness, and affecting it melting temperature and color.

 

Gold Color

Whereas most other pure metals are gray or silvery white, gold is yellow. By melting it with other alloys, its color can be changed, such as rose gold, which is created by adding various amounts of copper and silver, as indicated in the triangular diagram to the left. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. However in the European union, nickel has been banned from use in the creation of white gold alloy due to its allergenic effects on skin.

 

Gold Carat and purity

Pure (fine 24k) gold, it is usually mixed with other base metals to create and alloy for use in jewelry. The greater amount of alternative metals added to the fine gold the greater affect on altering its hardness, flexibility, melting point, color and other properties.
Gold caratage used in jewelry is typically 22k, 18k, 14k, 10k or 9k. The greater percentage of other base metals such as copper or silver, the lower the carat value of gold. Fine jewelry is usually made in 14K or 18K. In Asia it is not uncommon to find 22k gold. However gold with a purity of 22k is softer and can wear down more easily with everyday use. 
The carat system is increasingly being replaced with the millesimal fineness system, which measures gold purity by the amount of fine gold parts out of one thousand. I.e. 24k is 999 or 1000 parts out of 1000 parts fine gold. 18K has 750 parts fine gold and 250 parts base metals.

 

 

The base metals that are added to fine gold also affect its color. White gold is created by adding silver, palladium or sometimes nickel. Rose gold is created by adding copper. The greater amount of alternative base metals added to the gold alloy, the paler the color of the gold.
White gold in its bare state is not usually white like Platinum, but rather off white or yellowish in tinge. Jewelry manufacturers often plate white gold in Rhodium solution to create a true silver color. Especially on rings that are susceptible to wear the plating often wears off after a while and needs to be renewed. It is unlikely for yellow or rose gold to change color as they are not usually plated. 

 

 

Gold Carat Purity

Gold Parts Purity

24 Carat

999 -1000

22 Carat

916

21 Carat

875

20 Carat

833

18 Carat

750

15 Carat

625

14 Carat

585

10 Carat

417

9 Carat

375

8 Carat

333

1 Carat

042

   

 

The base metals that are added to fine gold also affect its color. White gold is created by adding silver, palladium or sometimes nickel. Rose gold is created by adding copper. The greater amount of alternative base metals added to the gold alloy, the paler the color of the gold.

White gold in its bare state is not usually white like Platinum, but rather off white or yellowish in tinge. Jewelry manufacturers often plate white gold in Rhodium solution to create a true silver color. Especially on rings that are susceptible to wear the plating often wears off after a while and needs to be renewed. It is unlikely for yellow or rose gold to change color as they are not usually plated.

 

Gold-filled jewelry

… also known as "rolled gold" or "rolled gold plate" is composed of a solid layer of gold bonded with heat and pressure to a base metal such as brass. Some high quality gold-filled pieces have the same appearance as 14 karat (58%) gold. In the USA the quality of gold filled is defined by the Federal Trade Commission. If the gold layer is 10 kt fineness the minimum layer of karat gold in an item stamped GF must equal at least 1/10 the weight of the total item. If the gold layer is 12 kt or higher the minimum layer of karat gold in an item stamped GF must equal at least 1/20 the weight of the total item. The most common stamps found on gold-filled jewelry are 1/20 12kt GF and 1/20 14kt GF. Also common is 1/10 10kt. Some products are made using sterling silver as the base, although this more expensive version is not common today.

"Double clad" gold-filled sheet is produced with 1/2 the thickness of gold on each side. 1/20 14Kt double clad gold-filled has a layer on each side of 1/40th 14Kt making the total content of gold 1/20. The thinner layer on each side does not wear as well as single clad gold-filled.

The Federal Trade Commission allows the use of "Rolled Gold Plate" or "R.G.P". on items with lower thicknesses of gold than are required for "gold-filled." A 12 kt gold layer that is 1/60 the weight of the total item is designated as 1/60 12kt RGP. This lower quality does not wear as well as gold-filled items.

Gold-filled items, even with daily wear, can last five to 30 years but will eventually wear through. The gold layer on gold-plated jewelry varies greatly depending on manufacturer, so there is no single, simple comparison. Gold-filled items are 50 to 100,000 times thicker than regular gold plating, and 17 to 25,000 times thicker than heavy gold electroplate (sometimes stamped HGE or HGP—usually found on flashy cubic zirconia "cocktail rings").

  

Platinum

 

The name Platinum is derived from the term ‘platina del Pinto’ which means little silver of the Pinto river. In its natural form it is a gray-white metal and one of the rarest elements on earth 80% of the worlds production coming from South Africa.

Like gold it has a remarkable resistance to corrosion, and has a higher melting point then gold. It is scarcer than gold with only a few hundred tonnes produced annually and there for considered a high value precious metal usually of greater monetary value then gold.

It is a lustrous metal and extremely malleable not oxidizing an any temperature. Due to its density resistance to wear, it is much more difficult to use than gold, in the creation of jewelry, melting at a much higher temperature. Casting platinum is an art in itself requiring specialized techniques and skill. The jewelry tools and polishes used in platinum jewelry manufacturing are much more susceptible to wear and tear.  Being a white metal that doesn’t fade or  tarnish is well suited for making fine jewelry.

Platinum in jewelry is usually 90–95% of the alloy and unlike white gold which is often plated with Rhodium to give its shiny silver color, Platinum’s color is naturally white an lustrous when polished with minute surface scratches called its patina.

Due to a higher density then gold, Platinum is 11% denser then fine gold and 42% denser then 18K gold. So a ring weighing 4.5 Grams in 18K gold will weigh almost 6.40 Grams in Platinum.


Silver 

 

Silver often used in jewelry creation is a very pliable and slightly harder than gold. With its brilliant white metallic luster it can be brought to a very high state of polish

Contrary to popular perception, Silver is stable in pure air and water, however it tarnishes when exposed to air or water containing ozone or hydrogen sulfide, the latter forming the a black layer of silver sulfide which can be cleaned with silver cleaners and even some house hold detergents. Silver jewelry that is worn or kept in the sea side with a higher level of humidity, will naturally tarnish at a higher rate due the higher concentration of ozone and hydrogen sulfide in the air.

Silver is dramatically affected by air pollution, notably what are known as sulfides (sulphides). Fumes from cars,  electricplants burning coal, generating air pollution such as sulfur dioxide, pollutes the air and will tarnish silver much faster.

Tarnishing will first turn silver yellow, then form golden patches, and then a purplish film, finally turning dark grey and even black. By the time it reaches this stage the damage can be irreversible. If you live in a humid areas where is there is a high concentration of pollution or near a power plant, be careful to keep your silver jewelry clean. Don’t let your silver jewelry or cutlery for that matter come in contact with eggs which are rich in sulfides, as they will quickly tarnish.

The obvious advantage of silver is that is a fraction of the cost of gold or platinum and if kept clean and protected, will maintain a beautiful luster.

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 an alloy consisting of at least 90.0% fine silver can be marketed as "silver" (thus 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. Britannia silver is an alternative, hallmark-quality standard containing 95.8% silver, often used to make silver tableware and wrought plate. Sterling silver jewelry is often plated with a thin coat of .999 fine silver to give the item a shiny finish. This process is called "flashing". Silver jewelry can also be plated with rhodium (for a bright, shiny look) or gold.

Silver is much cheaper than gold, though still valuable, and so is very popular with jewelers who are just starting out and cannot afford to make pieces in gold, or as a practicing material for goldsmith apprentices. Silver has also become very fashionable, and is used frequently in more artistic jewelry pieces.

 

 

Assay Marks controlling metal quality

In most countries around the world the purity of gold alloy is usually stamped or lasered on the jewelry. The quality or standard of gold purity is often managed by the local assay office, which tests the quality of the metal used.

In the UK and Europe there are strict standards regarding these tests and jewelry that passes is given an Assay Hallmark. This mark is used not only for gold, but also for Platinum and Sterling silver.

In 1973 legislation was brought into the EU to standardize controls of precious metals. Countries participating in this system test the metals to a common standard stamping or lazering the metal that reaches the required standard with a Common Control Mark (CCM), attesting to the material's fineness. The motif of the CCM is the balance scales, superimposed, for gold, on two intersecting circles; for platinum, a diamond shape and for silver a mark in the shape of the Latin letter "M".

This mark is used in the following countries: Austria, Cyprus, the Czech Republic, Denmark, Finland, Great Britain, Hungary, Ireland, Israel, Latvia, Lithuania, the Netherlands, Norway, Poland, Portugal, Sweden, Switzerland and Ukraine

The most significant item currently up for debate is the recognition of palladium as a precious metal. Some member nations recognize palladium as a precious metal while others do not

  

Chart showing the density of comparative precious metals.  
(Back to Top)

 

 

Platinum

Fine Gold

22 K Gold

18K Gold

14 K Gold

10K Gold

9K Gold

Fine Silver

Sterling Silver 925

Platinum

1.00

0.90

0.82

0.70

0.60

0.53

0.53

0.49

0.48

Fine Gold

1.11

1.00

0.91

0.78

0.67

0.59

0.58

0.54

0.54

22K Gold

1.22

1.10

1.00

0.86

0.73

0.65

0.65

0.60

0.59

18K Gold

1.42

1.28

1.16

1.00

0.85

0.76

0.75

0.69

0.68

14K Gold

1.66

1.50

1.36

1.17

1.00

0.89

0.88

0.81

0.80

10K Gold

1.88

1.69

1.54

1.32

1.13

1.00

0.99

0.92

0.90

9K Gold

1.90

1.71

1.56

1.34

1.14

1.01

1.00

0.93

0.92

Fine Silver

2.04

1.84

1.68

1.44

1.23

1.09

1.08

1.00

0.99

Sterling Silver

2.07

1.87

1.70

1.46

1.25

1.11

1.09

1.01

1.00

   

 

Weights &  Measurements

In many countries around the world, jewelry metal is weighed in grams. However the commodities market value precious metals in troy ounces and in the USA precious metals are also measured in penny weight DWT.

 

The following conversion table in shows the formula:

 

Troy Ounce

Gram

Penny Weight DWT

1.00

31.104

20

 

Read 4282 times Last modified on Friday, 12 May 2017 18:56

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