Tuesday 29 March 2016

All that glisters is not gold; Often have you heard that told:

All that glisters is not gold;
Often have you heard that told:
The Merchant of Venice- William Shakespeare

The Latrobe nugget, 717 grammes of crystallised gold
discovered in Australia 1853

Gold (Au) is a highly sought-after rare metallic element. Pure gold has an attractive bright yellow colour. Gold is a soft metal and is often alloyed (combined) with other metals such as silver, copper, nickel, and zinc to make it more durable and change the colour. It is non reactive to air and water and malleable making it ideal to been used for jewellery, money and ornamentation symbolising wealth and prosperity.
Like other precious metals, gold is measured by troy weight and by grams. When it is alloyed with other metals the term carat (or karat in the USA) is used to indicate the amount of gold present. Pure gold is twenty-four twenty-fourths (24/24ths) gold, and is called 24-carat gold. Gold that is 18-caret gold is eighteen twenty-fourths (18/24ths) gold and six twenty-fourths (6/24ths) other metals. 
Carat Percent Gold Hallmark
24- 100% gold -N/A
22- 91.6% gold -916
18- 75% gold -750
14- 58.5% gold -585
9- 37.5% gold -375

Alloys added to colour gold.
yellow gold- silver copper

white gold- zinc, copper, tin and manganese
rose gold- copper and silver
green gold- high proportion of silver or cadmium
blue gold- iron 
grey gold- iron
Plan A
For hundreds of years alchemists toiled in their laboratories to produce a mythical substance known as the philosopher’s stone. The stone was said to enable, as well as immortality and other phenomenon, chrysopoeia- the transmutation of base metals such as lead into gold.
The Famous Philosophers Stone
(not really, artistic impression)

Famous alchemists included Sir Isaac Newton and Nicolas Flamel. The alchemists were working on the theory that lead and gold were compounds, the periodic table wasn't to be developed for hundreds of years. They did not know that lead and gold were different elements.
Amazingly in 1980 scientists succeeded in turning bismuth (next to lead on the periodic table) into gold – all you need is a particle accelerator and a vast supply of energy. Sadly the amounts produced were negligible and with a cost of more than one quadrillion dollars per ounce, (in the USA a quadrillion is 1,000,000,000,000,000. or 1015not at all feasible, the current price is $1,220 per ounce approx.

Plan B
If you can't make gold, make something that looks like gold.

Is an alloy of Copper and Zinc made to imitate gold. It was developed at a time where the only legal standards of gold were 18ct and 22ct and before many of the worlds largest gold sources were discovered. Gold was an expensive purchase and 9ct carat gold was not introduced as a legal standard until 1854. It was invented by a London clock maker Christopher Pinchbeck (1670 to 1732 approx.) It had a bright gold colour that didn't fade or rust and was much more affordable than the real thing. This early Pinchbeck was beautifully created and finished to imitate fine jewellery and was used as "traveling jewellery" by the rich at risk of robbery from highwaymen and thieves. Such was its success that many tried to copy and these poor imitations led to Christopher's son, Edward Pinchbeck putting an advert in the Daily Post of July 11, 1733, headed "Caution to the Publick." in attempt to protect his business and reputation. He shrewdly kept the “recipe” and method of production a secret in his life time so only he could make the metal. The material is thought to be three parts zinc and 4 parts copper and possibly with a slight wash of gold on the surface to prevent tarnish.
click here to buy this Georgian, pinchbeck cuff bracelet.

The of fame Pinchbeck spread to France and the alloy was in considerable demand and again subject to imitation. A Lille jeweller called Rentz, created a similar alloy but it it didn't keep its colour. It was perfected by a jeweller named Leblanc, who managed to produce a good imitation named "
similor". It proved to be so popular that the goldsmiths of the day started legal proceedings about its use. The result was that the alloy was only allowed to be used for such things as shoe buckles, buttons etc so as not to compete with the regular goldsmith's work. Old texts refer to other alloys that were used to imitate gold including Mannheim or Dutch Gold, Prince Rupert’s Metal or Prince's Metal, Tombac. Pomponne is the name given to all the different alloys with a copper base that imitate gold. Alloys bearing a close resemblance to Pinchbeck continued to be used well into the nineteenth century until the process of electro-gilding made it easy and cheap to deposit a layer of gold on any metal as required.
The term pinchbeck has become to mean sham, spurious, or counterfeit and is often associated with fake jewellery. Ironically, Pinchbeck Jewellery is once again sort after and highly collectable and the consumer has to be wary that they are in fact purchasing real Pinchbeck and not an imitation.

Gilding is the process of applying a fine layer of gold to the surface of a less valuable material. It is an ancient skill and in the British Museum are silver nails with gold foil wrapped around the top. These were used to secure gold foil on a frieze in the Temple of the Eyes at Tell Brak one of the great cities of northern Mesopotamia (now known as Northern Syria) and estimated to be from early in the 3rd millennium B.C. Examples remain of the Egyptians using gold foil to adorn wood and metal in tombs, coffins, sarcophagi and other objects. There are also Egyptian paintings that show goldsmiths making the foil. Initially the foil was wrapped around the objects then techniques developed to attach the gold to the substrate such as burnishing (polishing to create a smooth surface) and using adhesive from animals or vegetable such as egg white.
The Romans also used gilding and Pliny the Younger in his writings discusses the costliness of using mercury in the gilding process. But by the 3rd and 4th centuries AD the use of mercury had become the standard method and would remain so up to 19th century.
Mercury gilding of metals was a hazardous process and was replaced by electrolytic gilding when electrical batteries were invented in the early 1800's.

In ancient South American a method called electroless gilding was used. They used the natural electrochemical potential difference (the exchange of electrons between substances) of gold and copper to obtain thin gold deposits from gold solutions on their jewels or ritual objects. A technique that is still used in the electronic industry. They also invented depletion gilding- a technique to produce a high-purity gold surface by removing everything that is not gold. Tumbaga- was an alloy of gold, copper and silver used extensively by Pre-Hispanic American metal smiths. Its relatively low melting point and malleability made it ideal to be made into detailed objects. The alloy could be made to look like pure gold by treating the finished surface by etching (applying an acid solution) to dissolve the copper and then hammered or burnished to join the gold, creating a uniform gold surface.
A tumbaga pendant: male shaman holding rattles, from Panama; circa A.D. 700 to 1500.

Powder Gilding
Gold foils or leaves were ground into a fine powder which was then mixed with a binder and applied to a surface. 

Ormolu is the finish used on decorative mountings of furniture, clocks, lighting devices, chandeliers and porcelain to imitate gold. The manufacture of true ormolu used a process known as mercury gilding or fire gilding. A solution of nitrate of mercury was applied to a piece of copper, brass, or bronze, followed by the application of an amalgam of finely ground gold and mercury. The item was then heated over an open fire until the mercury burned off (creating toxic fumes) the gold remained, adhered to the metal object. The process was repeated several times until a thick enough layer of gold had been created that could be left mat or was burnished with a heliotrope stone. Most mercury gilders died by the age of 40 due to exposure to the harmful mercury fumes.
 "Hang him; a gilder that hath his brains perished with quicksilver is not more cold in the liver".—John Webster, The White Devil, 1612.
Because of the impractical cost and health risks ormolu pieces were no longer produced after the early 1800s.
1812 Rare English Ormolu and Marble Mantle Clock

Bronze Doré The French referred to ormolu as bronze doré.

Gold Leaf Gilding
Gold Leafing or mechanical surface gilding is a technique of bonding very thin sheets of pure or nearly pure gold to a surface. Gilding was used for books, religious objects, pottery and ornaments. The use of real gold as well as imitation gold leaf (Dutch leaf) was common throughout Europe from the early middle-ages forward.
Mechanical surface gilding involves the use of a special adhesive called gold size, this can be either water or oil based. The surface to be gilded needs to be prepared and primed. Then an even coat of gold size is brushed onto the surface to be covered and left to dry to the correct tack (degree of stickiness) for the gold leaf to adhere to. The gold leaf is laid on the prepared surface usually with a soft brush, then gently pressed onto the surface, it is not cut to size first as it only adheres where the size has been applied. When the size has fully hardened the applied gold leaf can be burnished to a smooth finish to bring out the lustre of the gold leaf.
Using a non-gold leaf has been around since at least the 1500’s as a decorative replacement for costly gold. There are a number of different types of imitation leaf including:
  • Abyssinian Gold (alloy of copper and tin).
  • Ducat Gold (alloy of copper and aluminium).
  • White Metal (alloy of copper and aluminium).
  • Dutch metal (alloy of copper and brass).

Dutch metal leaf is by far the most common alloy used in gilding and is still commonly employed for gilding today.

Keum-boo (Korean for attached gold) is an ancient Korean gilding technique still being used in Jewellery making today. Pure gold and silver have similar atomic structure and heating them and applying pressure allows an exchange of electrons between the metals and creates a permanent bond. This technique depends on the surface having a layer of fine silver before heating and applying thin sheets of gold to the silver, to make silver-gilt. This technique is used in many cultures, including Chinese, Japanese and in the West to bond gold to other metals, including iron, copper, aluminium, gold alloys, white gold, palladium and platinum. 
click here to see  modern Keum-Boo

Gold-Plated Jewellery
Electroplating is the process of using electrical current to coat an electrically conductive object with a thin layer of metal. For gold plating it involves passing an electric current through a solution (electrolyte) containing gold dissolved as microscopic atoms. Two electrodes are submerged in the positively charged electrolyte (also known as plating bath) and connected to a circuit with a power supply. The object that is to be electroplated is connected to the negative terminal of the power supply (known as the cathode) a piece of gold is connected to the positive terminal (known as the anode). As the electricity flows through the circuit the electrolyte splits up and some of the gold atoms it contains are deposited in a thin layer on top of one of the cathode and gold atoms move from the anode into the electrolyte. 
When the item is new, the colour of the gold plate is similar with real gold jewellery. Normal electroplating for jewellery puts a layer of between 1 to 20 microns of gold on to the base metal. The plating is not permanent and can rub off, the thicker the plate the longer it lastthe item can be re-plated. Plating can come in a variety of colours.
Gold vermeil is a form of plating where the base metal must be sterling silver, the gold layer must be 14ct or higher in purity and the thickness of the gold layer must be at least 2.5 microns. 
Gold-Filled Jewellery
Gold-filled jewellery is also known as "rolled gold" or "rolled gold plate." It is created by using heat and pressure to fuse a layer of gold to copper, brass or some other base metal. The bond produced is a permanent one. In order to be considered gold filled, the gold content must be 5% or 1/20 of the total weight. It is marked rolled gold plate, R.G.P., or plaqué d'or laminé.
Bonded Gold
Bonded gold jewellery is when a thick layer of gold allow is bonded to a base metal or sterling silver core, so that the item is about 10% gold by weight. The bonded gold layer must be at least 9ct gold, this also applies to gold plated and rolled gold items in the UK. 

In 2012 the British Hallmarking Council (BHC) clarified the legal position on marking bonded gold, rolled gold and gold plated products.

"The BHC further stipulates that, assuming the core is 925 ie Sterling Silver, the article should carry a full silver hallmark, or a 925 stamp if it is under the Hallmarking exemption weight for silver of 7.78 grams. Bonded Gold on a base metal core cannot be hallmarked. No stand-alone gold fineness marks will be permitted on bonded gold articles, because they are potentially confusing and misleading to UK consumers. It is not permitted additionally to mark the article 9k, 10k, 14k, 18k etc, as is common practice in the United States.
The only circumstance in which this is allowed is if the gold fineness is immediately preceded or followed by the words ‘bonded gold’, ‘rolled gold’ or ‘gold plated’. For example, an article with a silver hallmark (or 925 stamp on underweight articles) can be marked as follows ‘925 & 18ct bonded gold/rolled gold/gold plated’.
It is also emphasised that the bonded gold layer must be of a fineness of at least 375 parts per thousand and of a recognised in UK standard. So, for example, ‘bonded gold’ of apparently 10K can only be described as 9 carat. This follows the practice for gold plated and rolled gold articles in the UK.
The guidance applies to all bonded gold, rolled gold and gold plated silver articles below the 7.78 gram exemption weight for hallmarking, as well as for those requiring hallmarking. The exemption is an exemption from hallmarking itself, not from the requirements of every other part of the Hallmarking Act 1973."

Visit the London Assay Office

A note about Fools Gold.

The gold colour, metallic lustre and weight of Iron Pyrite meant it could be mistaken for gold by the inexperienced. Pyrite and gold do often form together and some pyrite deposits contain enough gold to justify mining. Marcasite jewellery is actually made from Iron Pyrite or Fools Gold. It does not actually contain the mineral marcasite. Pyrite was set into other metals to produce a sparkly effect.

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