Tuesday, 23 January 2018

There's a lot more to Garnets than you realise....

Garnet, the January birthstone, refers not to a single gemstone but to a mineral group made up of 15 different garnet species whose chemical and physical properties are closely related to one another. The differences in the chemical make up and structure creates garnets that are not just red but also green, colourless, pink, yellow, orange, purple, brown, black and the rarest colour is blue. Garnets have a high level of clarity, if you see blurring, clouding or lots of inclusions within a stone, its unlikely to be a garnet.

Garnet is a very common rock forming,hard mineral with the power to resist weathering and decay. It is found all over the world, the major mining sites include the Czech Republic, Greece, India, Madagascar, Russia, Sri Lanka, Tanzania and The United States.

There are six main garnet types that are used for gemstones:

Almandine: Is the most common and most widely used garnet type in jewellery making. Some almandine garnets contain inclusions that when polished correctly as cabochons display a 4-rayed star asterism, these are known as "Star Garnets". Almandine garnets are used mostly in industry (see below)
COLOUR: dark red, reddish brown, black. 
HARDNESS: 7.5-8.5 mohs scale
Star Garnet
courtesy of Maker Mends Ltd

Andradite: is a fairly common variety and can produce fine garnet gemstones. A desirable gem form of Andradite is the rare and expensive Demantoid, which is a transparent green variety.

COLOUR: Brown, reddish-brown, bronze, orange, yellow, green, brownish-green, grey and black. Occasionally it is iridescent and multicoloured with streaks of brownish yellow, reddish-brown and black.
HARDNESS: 6.5-7.5 mohs scale

Andradite (Madagascar).

Grossular: Is the most varicoloured form of garnet. It varies from dark to colourless. Grossular gem varieties include the green Tsavorite and the orange to orange-brown Hessonite.
COLOUR: Brown, orange, green, yellow-green and grey. Less often pink, red, and yellow. Rarely white and colourless.
HARDNESS: 6.5-7 mohs scale
Tsavorite garnet crystal from the Merelani Hills of Tanzania
Rob Lavinsky

Pyrope: is the most well known form of Garnet, less abundant but most commonly used in jewellery making. Pyrope is always red and gets its name from the Greek for fire and eye.
HARDNESS: 7-7.5 mohs scale
Pyrope Garnet Checkerboard Cut
courtesy of Maker Mends Ltd

Spessartine: Is known for its orange and reddish-orange colours. Was once quite rare but recently found in abundance in Tanzania, China and Pakistan.
COLOUR: Orange, brown, brownish-red, red, dark red, pink, yellowish-brown, yellow, grey, black. Sometimes multicoloured red and black.
HARDNESS: 7 mohs scale
Detailed close-up of a spessartine crystal from Pakistan

Uvarovite: Is a rarer member of the garnet group. It is deep green in colour due to chromium in its composition. Other forms of green garnet are due to chromium impurities and can sometimes be mistakenly labeled as Uvarovite. 
COLOUR: Green to emerald-green.
HARDNESS: 6.5-7 mohs scale
Uvarovite Crystals Saranovskii Mine Urals Region, Russia

Colour changing Garnets Pyrope–spessartine (blue garnet or colour-change garnet)
It was thought that garnets came in every colour but blue until blue garnets were discovered in the Bekily district in southern Madagascar in 1998. These garnets are bluish-green to greenish-blue in daylight with a strong change to intense purple or purplish-red under incandescent light. The change is due to relatively high concentrations of the element vanadium and low concentrations of the element chromium. The mine also has a variety of garnets that are greenish-yellow to yellowish-green in daylight and an intense pink to red under incandescent light.

Colour Change garnets from Madagascar

Colour changing garnets have also been found in Tanzania, Kenya and Sri Lanka but not of the larger size and intense blue of the garnets of Madagascar.

Interesting Facts and stories concerning Garnets.

Follow the trail of Garnets to find Diamonds
Most of the garnets found at the Earth's surface have formed within the crust but others are brought up from the mantle during volcanic eruptions. These deposits called xenoliths also contain diamonds, although for every diamond there are considerably more garnets. As the xenoliths weather, the garnets are washed downslope in soils and streams. These garnets serve as "indicator minerals" for geologists looking for diamond deposits they can follow the garnet trail to the source deposit and hopefully diamonds!

One of the Oldest Gemstones
The Earth is 4.6 billion years old and remnants of its early crust are extremely rare. In 2008 scientists from McGill University did tests on Bedrock along the northeast coast of Hudson Bay, Canada. They determined that the rock samples there were the oldest rock on Earth, ranging from 3.8 to 4.28 billion years old. The rock there is composed of the mineral amphibole and it contains abundant amounts of garnet. 
This can be seen in the image below as as large round "spots" in the rock, the oldest Garnet on Earth.
Credit: geologist Jonathan O'Neil of McGill University.

No wonder then that ancient civilisations around the world were able to find and use garnets
to adorn themselves. Artefacts set with garnets have been discovered in ancient burial sites across the world.
 Carved garnets were used as seals to stamp the wax that secured important documents. Garnets were used in the creation of protective amulets -  in Ancient Rome, garnet was worn by pregnant women as protection against death from post-partum haemorrhage. 
In Ancient Egypt amulets were worn to protect the body, bestow healing powers and bring good fortune. Some were worn in daily life but others were placed inside mummy wrappings to safeguard the individual on their journey and existence in the afterlife.
The use of materials relating to colour was very important. Garnet symbolised the extremes of anger, fire, victory and life. See below some examples of these ancient pieces, still in incredibly good condition.

Egyptian Cylindrical Tube Amulet, Gold, bronze, garnet.
On display at the Brooklyn Museum New York.

Ancient carved garnet seal made in Asia in 720 BC-700 BC
On display at the British Museum.

Gold necklace made up of cylinders decorated with filigree and inlaid with garnets. 
Made in southern Italy about 300-200 BC.
On display at the British Museum.
Gold disk with pierced decoration set with garnets
 Roman 3rd century AD
On display at the British Museum.

Double finger ring in gold set with 2 sardonyxes and a centre garnet. 
Roman 4th century AD
On display at the British Museum.

A cross belonging to one of the first Christians of Northern England.
On display at the Ashmolean Museum Oxford 

This gold and garnet cross was found in Burton Pidsea, East Yorkshire in the 1960's. It dates to the seventh century when Christianity was first being introduced to the Anglo Saxons in England. Examination showed that the garnets were set in a bedding of calcium carbonate, a technique common for Anglo-Saxon pagan jewellery of that time. Originally there would have been ninety-five set in the cross, only 58 survived - not bad considering the passage of time! 

A story from the Antiques Road Show
Jill Cousins was watching the Antiques Road Show when jewellery expert Geoffrey Munn showed some sketches of what he called his "most wanted" items. 

These sketches were comprised of 15 drawings of brooches in pencil, pen and watercolour. He had searched for 20 years for one of these brooches and had given up hope of ever finding one. Jill realised that sitting upstairs in her jewellery box was an old broken brooch given to her by her mother, who had in turn inherited it from her old primary school teacher. The brooch matched exactly one of the designs. The brooch was made from silver and engraved with the initials "J.P.M.S." has four turquoise forget-me-knots with a central red cabochon garnet heart. 

A few days after, she took the brooch into Gildings Auctioneers for their advice, they in turn contacted the Antiques Roadshow.
Mr Gilding, Mrs Cousins and the brooch were invited to a recording of the Antiques Roadshow where they surprised Mr Munn who went on to confirm its authenticity and valued the brooch for £10,000. The brooch was to go on to sell for £31,000.00 at auction in August 2011. The designs were by William Burges one of the greatest Victorian architects and designers.
Close study of the brooch revealed it to be engraved with the name "Seddon" and with further research, Mr Munn was able to reveal that Burges had made the brooch for his friend John Pollard, an architect who moved in the circle of the Pre-Raphaelites on the occasion of his marriage to Margaret Seddon in 1864. The discovery of a second brooch adds weight to the theory that these were made as gifts for bridesmaids or other members of the wedding party.
The brooch was sold to the Victoria and Albert Museum where it can now be viewed along with the original sketches.

The Subway Garnet
In New York, August 1885, during a sewer excavation on 35th Street, between 7th Avenue and Broadway,  a reddish-brown almandine garnet was uncovered 8ft underground. It had 24 natural facets, measured seven inches in diameter and weighed 9 pounds and 10 ounces and was estimated to be 430 million years old. Manhattan's bedrock is streaked with veins of coarse-grained granite bearing amethysts, opals, tourmalines, beryls, chrysoberyls and garnets although few of gem quality. A geologist for the American Museum of Natural History, Joseph J. Peters, stated it was one of the largest ever found in the USA. Several months later the garnet, which had been used as doorstop in a shop, was given to George F. Kunz, a geologist and member of the Mineralogical Club and was known as the Kunz Garnet.
In 1968, the garnet was later given to its current owner, the American Museum of Natural History, where it was displayed at the entrance to Mineral Hall. However, with over 100,000 specimens in the museum's mineral and gem collections only 2% of specimens can be displayed at any one time. At this moment the Subway Garnet is no longer on public display but you can make an appointment to view it.
The Subway Garnet
Credit: Fred R. Conrad for The New York Times

Bohemian Garnets (also known as Prague or Czech garnets)
These small fiery-red to ruby-red pyrope garnets have been mined for over 600 years in the
area once known as Bohemia. The Jewellery made here used the small garnets packed closely together to cover the piece and show very little metal setting. 
Victorian Bohemian Garnet Brooch
Anyone visiting Prague will find its streets full of jewellers selling garnet jewellery. Modern methods have seen the introduction of mass-produced machine pressed metal settings for the garnets. Not of the same quality of earlier years.

Other uses of Garnets
The majority of almandine garnets today are used as abrasives. The garnet is crushed, then graded by size and then made into sandpaper, sanding belts, discs and strips. Garnet particles are used to polish wood and optical glass.

Garnet particles are mixed with water and fired in a high-speed jet in a process known as water jet cutting. Water jet cutting slices through metal and even granite with precision and with less dust and noise than other cutting methods. See a video here of the process. 

Garnet is an ideal water filter media as it is a chemically inert and a non-metallic mineral.  

Garnet is also used in the manufacture of computer chips.

Monday, 30 January 2017

He clasps the crag with crooked hands; Close to the sun in lonely lands, Ring’d with the azure world, he stands.

Excerpt from The Eagle- Alfred Lord Tennyson
Published: 1851
Lapis Lazuli- (also known as lazurite and ultramarine pigment)
Have you ever visited the British Museum? There are hundreds of exhibits featuring ancient items of jewellery, many of which use Lapis Lazuli, a distinctive deep blue stone, in their design. In ancient times Lapis Lazuli was highly desirable, difficult to obtain and a symbol of wealth and prosperity, so only the most privileged could afford it. These days lapis lazuli is still a popular, relatively inexpensive, semiprecious gemstone used in modern jewellery.  Many of the ancient designs wouldn't look out of place in todays world.
The finest Lapis Lazuli is an intense blue and the word ‘azure’ that describes the deep blue colour of this stone has found its way into many languages. In Poetry, azure is often used to represent or refer to the sky or Heaven.

The name originates from the latin for stone “lapis” and the Persian "Lazhward", which was an area, known for its deposits of lapis lazuli (“stone of Lazhward”) Lajward.

Lapis Lazuli is a metamorphic rock composed of sodium, calcium, aluminium, silicon, sulphur, oxygen (Empirical Formula: Na3CaAl3Si3O12S). It is formed when limestone or marble, deep in the earth, has been subjected to extreme heat and pressure sufficient to change the chemistry of their constituent minerals. The result is the formation of the blue silicate lazurite, the distinctive blue component of Lapis Lazuli. Lapis often contains visible white calcite and golden grains of pyrite that mimic gold.

Image of Lapis Lazuli taken at the Natural History Museum
Colour: Deep azure blue to light blue, bluish green. (Hex: #26619c) (RGB: 38, 97, 156)
Hardness: 5.5-6

Lapis Lazuli was treasured by ancient civilizations and used for ornamental carvings, mosaics, wall coverings and it was fashioned into beads or cabochons and polished to use as a gemstone. In ancient Egypt it was used to carve scarabs, protective stones or amulets in beetle form that protected graves, houses or were given as a gift.

This lapis lazuli scarab has a hawk-head figure wearing a ram's-horn crown carved into the back. In his left hand is a staff from which a lotus blossom dangles. 4th century BC.
Scarabs were a common type of amulet, seal or ring bezel found in Egypt. They were made in the shape of the sacred Scarab beetle.

The Royal Cemetery of Ur is an archaeological site in southern Iraq (ancient Mesopotamia) which was excavated between 1922 and 1934 by Leonard Woolley in association with the British Museum and the University of Pennsylvania. The site contained a wealth of treasures amongst more than 2000 burials which took place between 2600 BC-2300BC. Especially significant was the Tomb of Queen Puabi, which was discovered relatively untouched, her body was covered in jewellery made out of beads of gold, silver, lapis lazuli, carnelian and agate. Many of these items are on display at the British Museum.
Exhibit 121412 at the British Musem

Drinking tube; consists of alternating gold and lapis lazuli cylinders enclosing a long silver tube; 

silver had perished and has been restored. Approximately 2600 BC- 2300 BC.Royal Cemetery (Ur).
Exhibit 121486 British Museum
Diadem (headband worn by royalty) consisting of 14 gold pendants attached to a band of three strings of in total 173 beads of lapis lazuli (84), cornelian and other stone beads, carved, perforated and polished. Approximately 2600 BC- 2300 BC. Royal Cemetery (Ur).
Exhibit 122324 British Museum
Choker; a neck ornament of triangular gold and lapis lazuli beads; three string holes. 

2600BC Royal Cemetery (Ur)
Sapphires were not known before the Roman empire and many scholars agree that lapis lazuli is actually the stone meant for the term “sapphire” in the Bible.  
Pliny the Elder (a Roman author and naturalist) described Lapis Lazuli in his work The Natural History, “For sapphiros, too, is refulgent with spots like gold. It is also of an azure colour, though sometimes, but rarely, it is purple;" 
Engraved Gemstone with Mercury (Hermes)
First–third century CE
Lapis Lazuli
Indiana University Art Museum, Burton Y. Berry Collection, 64.70.49

This is an example of a Roman Lapis gemstone carved with an image of Mercury the messenger of the gods. 
Early references to the mining of lapis lazuli were in Persia, Tibet and China. Today it is still mined in varying qualities in the former Soviet Union, Asia, South and North America and Africa. However, the finest quality stone comes from the mines in Afghanistan in the remotest area of north-eastern Afghanistan. In the mountains of Badakhshan, is the mine Sar-i Sang (a name meaning "place of stone"). It is estimated to be 7,000 years of age and believed to be the oldest continuously-operating mine in the world. Throughout recorded history, people have come here seeking lapis lazuli, which exists here in the purest form and in the greatest quantity known on Earth.

Take a look here at a short video about the mining of Lapis, a highly risky occupation with little reward for the miners.


In the past Lapis was ground and processed to make the pigment ultramarine for tempera paint and oil paint. The name “Ultramarine” is derived from the Latin “ultramarines”, meaning "beyond the sea" as it was originally imported from Asia by sea. 
Vincent Van Gogh – Starry Night

The painting was investigated by the scientists at the Rochester Institute of Technology and the Museum of Modern Art in New York. The pigment analysis has shown that the sky was painted with ultramarine and cobalt blue.
The earliest use of lapis lazuli as a pigment were found on the cave paintings of the Temples of Bamiyan in Afghanistan, dated to be from the 5th and 9th centuries A.D. 

To produce the pigment from lapis lazuli, the blue lazurite has to be separated from the other minerals present. Lapis Lazuli was ground and mixed with molten wax, resins and oils, wrapped in a cloth and kneaded with a caustic solution called lye to isolate the blue particles from the rest of the mixture. It was an expensive colour to purchase because of the very high quality of stone required and because of the drawn out complicated method of extraction. The use of Ultramarine with gold in medieval times was popular for use in sacred paintings and manuscript illuminations. 

Miniature of Christ in glory holding a globe and blessing the Virgin illuminated by Pacino di Buonaguida, central Italy (Tuscany), c.1335 -c.1340

European artists used the pigment in moderation, reserving the ultramarine blues for the robes of Mary and the Christ child. As a result of the high price, artists sometimes economised by using a cheaper blues, such as azurite, for under painting.

In 1806 the chemical composition of ultramarine was identified and in 1828 a process to manufacture a synthetic ultramarine which could be made economically was discovered. The first artist accredited with its use was J.M.W. Turner in 1834 and from then on nearly all of the pigment used in painting was of the synthetic variety.


Gilson LapisA synthetic simulation of Lapis Lazuli has been created using the Gilson process. Although Gilson Lapis may look similar to Lapis Lazuli, it is not made of the same composition, lacking the natural random patterns displayed in most true Lapis Lazuli.

Swiss Lapis- Jasper that is dyed blue to simulate Lapis Lazuli.
Howlite- may also be dyed an ultramarine blue to simulate Lapis Lazuli.


The colour of Lapis Lazuli is natural and it is generally not treated, though occasionally lighter coloured stones may be dyed a deeper blue.

Similar Minerals
Azurite crystals on display at the Natural History Museum (found Chessy, Rhone, France)
Azurite-  is a common mineral found in many locations worldwide. Areas that produce excellent crystals include in France, Italy, Russia, Morocco, Namibia, the United States, Mexico, Australia, and China. Azurite is a much softer mineral but can be used for jewellery such as beads and cabochon, however, heating destroys azurite that limits its uses. Azurite was also used as a blue pigment since antiquity and was a major source of the blues used by medieval painters. Whilst true lapis lazuli was chiefly supplied from Afghanistan, azurite was a common mineral in Europe at the time. 

Sodalite- is sometimes confused with lapis lazuli. Some specimens have a similar colour and the presence of white veining is found in both materials. Sodalite is named in reference to its sodium content. It is used for carvings and some jewellery pieces.
Hardness: of 5.5 to 6.

What to look for when choosing Lapis Lazuli Items

Mined Lapis Lazuli rough pieces can be very large and the larger sized pieces are often carved into objects of art. A good lapidarist can shape and size smaller pieces for use in designer jewellery.
The most valued colour in a lapis lazuli is the azure blue of mid to dark tones with no visible specks or streaks of white calcite and little or no pyrite, although many prefer lapis with an even sprinkling of golden pyrite flecks.
Vintage 1950s Mid Century Tiffany & Co. Lapis Lazuli & Diamond Cocktail Ring in 18ct Yellow Gold

Avoid lapis that looks dull and green, this is the result of an excess of pyrite. Lapis with white calcite streaks is less attractive and therefore of less valuable.

Looking after your Lapis Lazuli Jewellery.
  • Remove jewellery when undertaking activities such as sports, swimming, gardening etc. 
  • Remove jewellery when sleeping. 
  • Don't allow jewellery to come in contact with chemicals, chlorine is particularity damaging. Rinse off any chemicals that come into contact with your jewellery straight away. 
  • Remove jewellery before bathing and apply lotions and perfumes before putting on your jewellery. 
  • Store jewellery items separately so that pieces do not tangle, rub or scratch against each other. Use a soft lined (satin or velvet etc) case or bags. 
  • If you need to clean your lapis jewellery use a mild soap and soft cloth. Avoid mechanical cleaning, such as steam or ultrasonic systems and chemical solvents.
  • Threaded beads should be checked periodically to ensure the thread is still in good condition, get re-strung when necessary.


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.