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Chapter 1. Gold Nanoparticles in the Past: Before the Nanotechnology Era Catherine Louis

Chapter 1. Gold Nanoparticles in the Past: Before the Nanotechnology Era Catherine Louis

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gold, meteoric iron, silver and tin to create tools and possibly jewellery

ornamentation. Gold was most probably discovered as shining, yellow

nuggets. Although it can be easily worked because of its ductility, it is

not clear whether it was worked before copper.a

It is known that the Egyptians mined gold before 2000 BCE in Nubia.

The Turin Papyrus drawn during the reign of Ramesses IV (1151–1145

BCE) is the earliest known topographic and geological map.1 Along with

specifics of the geology and topography, it shows an ancient gold-working

settlement, gold-bearing quartz veins in Wadi Hammamat, a dry river bed

in Egypt’s Eastern desert. Large mines were also present across the Red

Sea in what is now Saudi Arabia. By 325 BCE, the Greeks had mined in

areas from Gibraltar to Asia Minor and Egypt. The Romans mined gold

extensively throughout the empire, developing the technology of mining

to new levels of sophistication. For example, they would divert streams of

water in order to mine hydraulically, and even pioneered ‘roasting’, the

technique of separating gold from rock.

Occasional passages on mining and metallurgy of metals can be

found in the works of Theophrastus (Greek, 372–288 BCE), Vitruvius

(Roman, 90–20 BCE), Strabo (Greek, 63/64 BCE–c. 24 CE), Pliny the

Elder (Roman, 23–79 CE) and Discorides (Greek, 40–90 CE). One important surviving document is the Leyden Papyrus X of the Museum of Antiquities in the Netherlands: it is the working notebook of a goldsmith and

jeweller, probably written in the early years of the fourth century. It gathers

111 recipes of refining, alloying and working of gold; some of them are

reported in Hunt’s paper2 (accessible online, free of charge).

Another important date for the history of gold is 1492, with the discovery of America and the beginning of massive expeditions and exploration

with the quest for the El Dorado, and the encounter with Native American

people, in Central and South America, with their extensive displays of gold

ornaments. The Aztecs regarded gold as literally the product of the gods,

calling it ‘the sweat of the sun’.

a One can read on some websites that the earliest traces of gold dated back to the Paleolithic period

40,000–10,000 BCE and were found in Spanish caves of Maltravieso; this is wrong according to

Dr Antoni Canals y Salomó (Universidad de Tarragona), a paleontolongist, specialist of this cave.



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Two hundred years later, in 1700, gold was discovered in Minas Gerais

in Brazil, which became the largest producer by 1720, responsible for nearly

two-thirds of the world’s gold output, but the production was in rapid decline

by 1760. 1799 is the year of the first discovery of gold in the United States,

when a 17-pound nugget was found in North Carolina. For the next 25 years,

North Carolina supplied all the domestic gold coined for currency by the US.

In 1848, John Marshall found flakes of gold near Sacramento in California,

triggering the California Gold Rush. In 1850, E.H. Hargraves, returning to

Australia from California, found gold in his home country within a week.

1868 saw the next major discovery, in South Africa, where G. Harrison

uncovered gold while digging up stones to build a house, and in 1898,

South Africa became the world’s top gold producer with a quarter of the

world production.

Up to now, a total of 161,000 tonnes of gold have been mined in human

history; this corresponds to the volume of a single cube 20 m on a side

(equivalent to 8000 m3 ). 75% of all gold ever produced has been extracted

since 1910. The typical annual production in recent years has been around

2,500 tonnes per year. In 2009, the largest producers were China (12.8%),

then Australia, South Africa and the United States (9.1% each). India is the

world’s largest consumer of gold (800 tonnes of gold every year), and the

largest importer; in 2008 India imported around 400 tonnes of gold.



1.1.2 Gold as jewels and artefacts

The most ancient gold artefacts were found in necropolis, but not in

Mesopotamia or Egypt as is often believed. The history of gold starts

long before the invention of writing and the establishment of the first cities

of Mesopotamia and Egypt (circa 2800 BCE). It starts around 4500 BCE

with ‘Old Europe’ civilisation in south-eastern Europe that was at that time

among the most sophisticated and technologically advanced regions in the

world. A necropolis with 294 graves dating to 4600–4200 BCE was discovered in 1972 in Varna on the Black Sea coast, which is located in modern-day

Bulgaria. The graves contained some 300 objects made of pure gold: sceptres, axes, bracelets, other decorative pieces and bull-shaped plates. These

objects attest to the high-level skill of goldsmithing. They can be seen at



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the Varna Archaeological Museum and at the National Historical Museum

in Sofia.

Three important discoveries of gold artefacts were found in tombs dated

to circa 2500 BCE in three different geographical areas:

• The tomb of Djer at Abydos in Egypt. He was probably the third king of

the First Dynasty (c.2800 BCE). Although the tomb had been robbed, a

human arm was discovered near the entrance, still wearing four golden

bracelets (shown in the Cairo Museum).

• The tomb of Queen Pu-Abi in southern Iraq. She was an important figure

who lived about 2600–2500 BCE, during the First Dynasty of Ur of the

Sumer civilisation. Among other excavations of the Royal Cemetery of

Ur, discovered between 1922 and 1934 by Sir Leonard Woolley, her tomb

had been untouched by looters. It revealed several gold ornaments and a

profusion of gold tablewares, golden beads for necklaces and belts and

golden rings and bracelets. The treasure was split between the British

Museum in London, the Penn State Museum in Philadelphia, and the

National Museum in Baghdad.

• The so-called Gold of Troy treasure hoard, also called the Treasure of

Priam by Heinrich Schliemann who excavated it in 1873, on the ancient

site of Troy in the area of the city of Çanakkale in Turkey. Dated to

2600-2450 BCE (i.e. 1,000 years before the Trojan war!), it showed a

range of gold-work from jewellery to a gold ‘gravy boat’ weighing 600 g.

Most of the treasure, which was first in Berlin, is now in the Pushkin

Museum in Moscow.

A millennium later (1200 BCE), probably the much better known hoard

of gold was found in the tomb of Tutankhamun in Egypt (1333–1324 BCE).

It contained the largest discovered collection of gold and jewellery, including a gold coffin. At the same period, pre-Columbian goldsmiths started

producing gold items in South America. Their art reached its zenith during

the Chimu civilisation between the twelfth and fifteenth centuries, but was

stopped by the mass looting of the ‘conquistadors’.



1.1.3 Gold for monetary exchanges and the gold standard

Gold has been also widely used throughout the world, as a vehicle for

monetary exchange, even before the establishment of a gold standard, a

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monetary system in which the standard economic unit of account is a fixed

weight of gold.

Egyptian Pharaohs began to commission gold tokens around 2700 BCE,

but these tokens of variable purity were used as gifts, not for commerce.

Much later, circa 600 BCE, the first gold coins known were minted by King

Alyattes in Lydia (present-day Turkey). As a matter of fact, they were made

of electrum, a natural alloy of gold and silver arising from alluvial deposits

of the river running through Sardis, the Lydian capital. At the same period,

600–500 BCE, another gold coin, the Ying Yuan, was used in the kingdom

of Chu in China.

Gold coins were used in some of the great empires of earlier times,

such as the Byzantine Empire. But after the ending of this empire, the

‘civilised world’tended to use silver coins. Paper money was first introduced

in China between the seventh and fifteenth centuries, and then in Europe in

the seventeenth century. It was a promissory note, i.e. a receipt redeemable

for gold and/or silver coins. In 1816, England ended its policy of bimetallic

standard (gold and silver) and adopted a single gold standard while the

rest of Europe remained on a silver or bimetallic standard. Between 1872

and 1900, most major countries abandoned silver or bimetallic systems and

achieved gold convertibility. At the beginning of the First World War, the

gold standard was at its pinnacle, with 59 countries having adopted this

standard.

However, during the First World War, governments had to face the huge

war effort and boosted banknote printing, while international trade dropped

dramatically. At the end of the war, all the countries had left the gold standard. However, England returned to the gold standard between 1925 and

1931, and France was the last country to abandon the convertibility in 1936.

After the Second World War, the Bretton Woods Agreements (22 July 1944)

created a system of fixed exchange rates, and gold was replaced by the US

dollar. Nevertheless, nowadays, gold remains a safe investment.



1.1.4 Gold for human well-being: food, drinks and medicine

Pure metallic gold is non-toxic and non-irritating when it is ingested. Metallic gold has been approved as a food additive in the EU (E175 in the Codex

Alimentarius). As gold leaf, it is sometimes used as food decoration in

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China, Japan, India and also in Europe (for instance in France on ‘palet

d’or’ chocolate). Gold leaves are also used as a component of alcoholic

drinks, such as ‘Goldschläger’, ‘Gold Strike’ and ‘Goldwasser’.

Since the discovery of gold, people have thought of it as having an

immortal nature and have associated it with longevity, probably because of

its resistance to chemical corrosion. Many ancient cultures, such as those in

India and Egypt, used gold in medicine but mainly for its magico-religious

power. However, gold played almost no role in rational therapeutics. An

exception is China, with the earliest application of gold as a therapeutic

agent back in 2500 BCE. Pliny the elder, in the first century, reported gold

for healing fistulas and haemorrhoids. The uses of gold were limited because

at that time people did not know how to dissolve it and make it soluble. It was

with the medieval period and the European (al)chemists that gold became

a prominent medicinal element, with the idea that the elixir of life, Aurum

potabile, can restore youth. Aurum potabile was closely related with the discovery of aqua regia (a mixture of hydrochloric and nitric acids), the ‘royal’

solvent of gold. A gold cordial was advocated in the seventeenth century

for the treatment of ailments caused by a decrease in the vital spirits, such

as melancholy, fainting, fevers and falling sickness. Later, in the nineteenth

century, a mixture of gold chloride and sodium chloride was used to treat

syphilis.

The use of gold compounds in modern medicine began with the discovery in 1890 by the German bacteriologist Robert Koch that gold cyanide

K[Au(CN)2 ] was bacteriostatic towards the tubercle bacillus. Gold therapy

for tuberculosis was subsequently introduced in the 1920s, but soon proved

to be ineffective. In contrast, gold therapy proved to be effective against

rheumatoid arthritis. Since that time gold drugs have also been used to treat

a variety of other rheumatic diseases such as juvenile arthritis, palindromic

rheumatism and various inflammatory skin disorders such as pemphigus,

urticaria and psoriasis.

Today, in allopathic medicine, only salts and radioisotopes of gold are

of pharmacological value, as elemental metallic gold is inert. However,

some forms of alternative or traditional medicine assign metallic gold a

healing power. The ayurvedic medicine in India, dated back thousands of

years and related to the medical use of metals and minerals, involves gold

in such medicines. For instance, Swarna Bhasma comprises globular gold

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nanoparticles with an average size of about 60 nm. Gold is considered to be a

rejuvenator and, as such, is taken by millions of Indians each year. A typical

daily dose corresponds to one or two milligrams of gold incorporated into

a mixture of herbs.

Metallic gold may also have a renewed potential in ‘modern’medicine as

colloidal gold nanoparticles, which could be used for imaging, diagnostics,

drug delivery or radiotherapy (see Chapters 10 and 11).

The malleability and resistance to corrosion make gold perfect for dental

use, although its softness requires that it is alloyed, most commonly with

platinum, silver or copper. So gold in alloys is used in tooth restorations,

such as crowns and permanent bridges. There are examples of its use by

the Phoenicians, the Etruscans and the Romans for restoration and also for

aesthetics reasons.

For more information on gold in medicine, the reader can refer to

Refs. 3–8 (free access) from which most of the information above has been

drawn.



1.1.5 Gilding gold and gold-like lustre

The use of gilded films of gold on oxide substrates to decorate glass, ceramic

and mosaics may be dated from the Roman period circa the first century, as

reported by Pliny the Elder, but wider use dates from the twelfth century.

Gold foil coating is the most ancient technique used, and tesserae of mosaics

(small block of material used in the construction of a mosaic) were the first

supports used. In this process, a few micrometers of thick gold foil is pasted

onto substrates of glass or ceramic with an adhesive agent, such as linseed

oil or egg white, covered with glass powder and heated. The most ancient

articles are probably the golden mosaics of the cupola of the mausoleum of

Galla Placida built in Ravenna in 425–443, but the peak of gold gilded glass

production is in the thirteenth and fourteenth centuries with the Mamelouk

production in Egypt and Syria, and also in the nineteenth century.

Gilded films must be distinguished from lustre, which is a surface layer

with a metallic appearance applied on glazed ceramics, i.e. on a surface

of terracotta covered by a glassy layer. Lustre exhibits various colours,

from gold to brown or red. However, in spite of the appearance, it does not

contain any gold, but only silver and copper metal particles in various sizes

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and compositions, dispersed in a glassy matrix with a gradient of size and

concentration.9−11



1.2 The First Uses of Gold Nanoparticles

The first use of gold nanoparticles is intimately related to the history of

red-coloured glass. The production of red glass (opaque) starts with the very

beginning of glassmaking in Egypt and Mesopotamia back in 1400–1300

BCE.12 The colour of this red glass was given by the addition of copper. The

origin of the red colour is debated, with some scientists stating that it is due

to metal copper nanoparticles, while others state that it is due to cuprous

oxide (cuprite) nanoparticles or to both. The origin of the coloration also

depends on the sites and dates of production, the method of preparation

and components of glass.13 The production of copper red glass is a real

challenge from a technological point of view because it requires a reducing

atmosphere; for this reason, red glasses are less frequent than other colours.

Another way of making red glass involves the use of gold nanoparticles.

According to most of the textbooks and technical encyclopedias on gold,

glass and ceramics, the production of the so-called ‘gold ruby glass’ did

not take place until the end of the seventeenth century. The discovery is

attributed to Johann Kunckel (c.1637–1703, Brandenburg) and that of the

gold preparation that is added to melted glass to give it the ruby red colour

is attributed to Andreas Cassius of Leyden in 1685.14 This is the so-called

Purple of Cassius, which is a precipitate obtained from the dissolution of

gold metal in aqua regia followed by the precipitation of metallic gold by

a mixture of stannous and stannic chloride.

As a matter of fact, the story of gold ruby glass begins long before, and

there is no break until the peak of its production at the end of the seventeenth

century.



1.2.1 The Lycurgus cup

Hence, the first milestone in the history of gold ruby glass is a Roman opaque

glass cup dated to the fourth century, the Lycurgus cup, which is exhibited at

the British Museum in London15 (Fig. 1.1). The carved decoration depicts

a mythological scene that is the triumph of Dionysus over Lycurgus, a king

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Fig. 1.1. The Lycurgus cup, late Roman, fourth century CE, probably made in Rome (from the British

Museum free image service). (a): illuminated from outside. (b): illuminated from inside.



of the Thracians (circa 800 BCE): one of Dionysus’ maenads, Ambrosia,

transformed into a vine by Mother Earth, holds Lycurgus captive while

Dionysus instructs his followers to kill him.

This cup shows a green jade colour due to the diffusion of light when it is

illuminated from outside (Fig. 1.1.a) and a deep ruby red one in transmission

when it is illuminated from inside (Fig. 1.1.b) (See also Section 1.3.1). A

detailed analysis of the Lycurgus cup, published in 1965 by Brill,16 revealed

the presence of minute amounts of gold (about 40 ppm) and silver (about

300 ppm) in glass. In 1980, a further analysis by Barber and Freestone17

attested the presence of nanoparticles of 50–100 nm in diameter by electron

microscopy, composed silver-gold alloy, with a ratio of silver to gold of

about 70:30. Later on, Hornyak et al.18 confirmed through a theoretical study

that the deep red colour of the Lycurgus cup due to light absorption around

515 nm is consistent with the presence of silver-gold alloy with Ag:Au of

70:30. (See Chapter 3 for optical properties of gold nanoparticles.)

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The British Museum experts believe that the colouring of glass using

gold and silver was far from routine during the Roman period since only a

limited number of other glasses appeared to have been coloured by gold.19

Moreover, no other glass of this period replicates the dichroic optical effect

of the Lycurgus cup. They conclude that the technology seems to have been

very restricted and did not outlast the fourth century.

However, a very recent study by Verità and Santopadre20 reports the

chemical analyses of nine flesh-tone glass tesserae of mosaics, arising from

nine important churches in Rome of the fourth to twelfth centuries. All of

them reveal that the flesh colour originates from the presence of 10–30 ppm

of gold or gold-silver alloy particles. Since a considerable number of fleshcolored glass tesserae were employed in mosaics of these churches, the

authors conclude that the colour was obtained routinely rather than by

chance, and that the Roman glassmakers mastered this complex coloration

process. Since there is no evidence that the Romans were able to produce

aqua regia to prepare gold chloride at that period, the authors propose that

the Roman glassmakers may have used silver slags without knowing that

they also contained gold, thus without knowing that gold was the actual

colorant of glass; they also propose that the colour arises from the local

dissolution of gold leaves and the formation of ‘droplets’ of gold ruby glass

since these droplets are commonly found in the gold-foil tesserae of Roman

mosaics.



1.2.2 Medieval period

There is written evidence that the (al)chemistsb of the Middle Ages knew

how to produce red-coloured glass with gold, although samples of such

glass have yet to be found.19,21 It should be noted that some textbooks

and websites state that the red colour of stained glasses of medieval church

windows is given by gold. However, in all cases analysed so far, the colorant

found is copper.19

Al Razi (865–925), a Persian scholar, philosopher and alchemist, reports

the earliest known written account of a gold ruby glass in his treatise Secrets

b Note that it is during the nineteenth century that a distinction is made between alchemists and

chemists.



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of Secrets. The instruction was to heat a very finely powdered batch of

different elements including gold powder for three days in a closed furnace

fuelled with very hard wood. In his paper, Sheybany22 concludes that this

may allow temperatures of 800–1000 ◦ C to be reached in a reducing atmosphere. Al Razi believed he had fulfilled the objective of the transmutation

of metals; in his treatise, he stated that this glass attracted gold and silver

like a magnet and that it could convert 1,000 times its weight into gold.22

It is important to stress that the main goal of the medieval alchemists was

the making of the philosopher’s stone. In alchemical writings, the philosopher’s stone is often described as a red substance, which is supposed to be

the key to transmutation of ‘impure’ base metals into gold, the unique pure

metal.



1.2.3 Fifteenth and sixteenth centuries

In the Bologna manuscript, Segreti per colori, written in the first middle of

the fifteenth century, three recipes of gold ruby glass are described. However,

according to Zecchin’s paper23 they are inconsistent. Later on, between 1458

and 1464, Antonio Averlino, also called Filarete, provided some technical

information on glass coloration in his Trattato di Architettura, and wrotes

‘It is also said that gold makes colour.’23

Georgius Agricola (1494–1555, Saxony), who is considered the founder

of geology, is supposed to have described the preparation of gold ruby glass

in De natura fossilium published in 154614,24 : ‘A famous variety of dyeing glass is made from gold and this is used to tint the glass clear ruby

red.’ As a matter of fact, according to Zecchin23 and von KerssenbrockKrosigk,25 this sentence is wrong and results from a mistake in the first

translation from Latin to English. However, there are several other writings

that refer to gold ruby glass during the sixteenth century. Benvenuto Cellini

(1500–1571), a famous sculptor and goldsmith in Florence, refers to a transparent red enamel discovered by an alchemist who was also a goldsmith.26

Later, Andreas Libavius (c.1540–1616), a German chemist and physician,

mentioned the red colour of gold dissolved in liquid to make red crystal

in Alchemia published in 1597. According to Polak,27 Andreas Libavius

based himself in this on two earlier ‘distillers’, the Neopolitan Giambattista Porta (1535–1615), author of Magiae Naturalis (1588) and Gerhard

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Dorn (c.1530–1584), the German author of Clavis Totius philosophiae

chymistica (1567).



1.2.4 Seventeenth century

L’Arte Vetraria is the first print book exclusively devoted to glassmaking.

It was published in 1612 by Antonio Neri (1576–1614), a Florentine priest,

son of a physician. In Book 7, Chapter 129, one recipe mentions the use

of gold to produce red glass. In short, the recipe, which is entirely reported

in Franck’s paper,24 involves the calcination of gold with aqua regia in a

furnace, which forms a red powder that is then added to glass. The recipe

attests that the potential of using gold as a red colorant was fully understood

in early seventeenth century.28 The only known gold ruby vessels of Italian

origin of that period are a series of ribbed bowls, ewers and bottles that King

Frederick IV of Denmark brought back from a trip to Venice in 1708–1709.

These artefacts are visible in Rosenborg castle in Copenhagen.

Antonio Neri’s book was then translated into English in 1662 by

Christopher Merrett (1614/5–1695); he added 147 pages of his own, from

other authors and his own observations. In 1679, the first German edition of

the Neri–Merrett book appeared, translated with further extensive addition

by the famous Johann Kunckel (cited at the beginning of Section 1.2) under

the title Ars Vitraria Experimentalis.

Other written sources were recently found by Zecchin in Murano

archives.23 A manuscript written by Giovanni Darduin (1585–1654), a glassmaker of Murano, provides a recipe of gold ruby glass among other glass

recipes of his and of his father who died in 1599. Two other recipes of

gold ruby glass were provided by Giusto Darduin (1661–1700) and one by

Antonio dalla Rivetta (1628–1695). Zecchin could not establish the existence of a relationship between the Italian branch and the German one and

Kunckel.23 However, he suggests that a relationship may have existed with

Bernard Perrot in France (see Section 1.2.4.3).



1.2.4.1 Purple of Cassius

As mentioned at the beginning of Section 1.2, the paternity of the purple

gold precipitate used for colouring glass, the so-called Purple of Cassius,

has been attributed to Cassius. As described earlier, the preparation involves

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