The British Crown Jewels include ceremonial pieces that will be presented to The King and The Queen Consort during their coronation at Westminster Abbey on May 6, 2023. Looking ahead to this historic occasion, Gem-A Tutor Pat Daly dives deeper into the Coronation Regalia, including St Edward’s Crown, the Sovereign’s Ring and the Sovereign’s Orb… 

The Crown Jewels incorporate the items presented to King Charles III and his wife, The Queen Consort, during the coronation ceremony in May 2023. The collection also includes important jewellery pieces and a selection of gold and silver plate used for banqueting, in church services and ceremonial occasions. They comprise more than 100 objects, set with over 23,000 gemstones, and when they are not in use, they are secured in the Tower of London, where many are on public display.

Crowns and other symbols have been used in the coronations of British monarchs for more than 1,000 years, but, with few exceptions, the oldest of those in use today date from the restoration of Charles II in 1660. Most of those used in earlier times were sold or destroyed by Parliament in about 1650, during the Civil War. A notable exception is the pearl-set silver gilt spoon from the 12th century, which is still used in the ceremony. 

In the traditional ceremony, the King enters the Abbey in procession, is acclaimed, and then anointed with holy oil by the Archbishop of Canterbury. He is then robed and returns to the coronation chair to be presented with the coronation regalia. These are taken from the altar, some to be held by him while others are returned to the altar. 

Among the most important pieces are St Edward’s Crown, two sceptres, the Sovereign’s Ring and the Sovereign’s Orb. 

St Edward’s Crown, with which the monarch is crowned, is little altered since it was made in 1661, except that it is now set with coloured stones instead of diamonds. It consists of a gold band decorated with crosses and fleur-de-lys, and arches surmounted by an orb and cross. All these elements contain rubies, sapphires, amethysts, garnets, peridots, zircons and tourmalines in enamelled settings. 

St Edward’s Crown, courtesy of Nathan Hughes Hamilton, Flickr (Creative Commons).

The Sovereign’s Sceptre with Cross is a gold rod set with a large pear-shaped diamond, topped by an amethyst orb and a cross. It is also decorated with bands of enamel and gemstones, including diamonds, rubies, spinels, and emeralds. The pear-shaped diamond was cut from the Cullinan diamond, the largest gem-quality diamond found. It had a rough weight of 3,106 carats and was polished into nine principal and 96 smaller stones, losing about 65% of its original weight. The nine stones are numbered in order of decreasing size, the largest, the Cullinan I, being set in the sceptre, measures about 59 x 45 mm, and weighs 530.20 carats. It is the largest polished white diamond in the world. Despite its great size, 74 facets were considered sufficient for this stone, compared with the 57 or 58 of a standard brilliant-cut diamond. The five largest of the Cullinan diamonds are set in the Coronation Regalia.

The second sceptre also has gem-set bands in enamelled settings and is topped by an orb and a white-enamelled dove. 

The Sovereign’s Ring is set with an oval sapphire overlaid with gold collets, set with square and baguette-shaped rubies in a cruciform pattern, and surrounded by diamonds.

The gold Sovereign’s Orb is set with bands of diamonds, emeralds, rubies, sapphires and pearls and is surmounted by a jewelled cross supported on a large step-cut amethyst, about 25mm wide, which rests on its table facet.

The King is also presented with ceremonial spurs, bracelets (armills) and a jewelled sword, the Sword of Offering, the handle and scabbard of which are adorned with leaf and flower motifs, among which the rose, thistle and shamrock are prominent, set with diamonds, emeralds, rubies and sapphires.

The crown is placed on the King’s head to complete this part of the ceremony, after which he moves from the coronation chair to the throne. The Queen Consort is then crowned and may receive jewelled sceptres and a ring set with a ruby and diamonds. The crown to be used is Queen Mary’s crown, made in 1911, consisting of a band with crosses and fleur-de-lys and arches supporting an orb and cross. All these parts are diamond-set and will include three of the principal Cullinan diamonds; a pear shape of 94.40 carats, a cushion weighing 63.6 carats, and a heart shape of 18.80 carats.

After receiving Holy Communion, the King exchanges St Edward’s Crown for the lighter State Crown and, carrying the Sovereign’s Sceptre and Orb leaves the Abbey in procession.

The Imperial State Crown is of a similar design to the other crowns used in the ceremony but is used for state occasions other than the coronation. It is of gold, set with more than 3,000 gemstones, mostly diamonds but also pearls, sapphires, emeralds and rubies. Several important stones are included in this number. 

The Imperial State Crown, courtesy of Michael Garnett, Flickr (Creative Commons).

The Black Prince’s ruby is a fine baroque unfaceted red spinel set with a smaller red stone in a gold collet. It weighs 170 carats, was bought in 1685 and is reputed to be the stone belonging to Edward, the Black Prince, and to have been worn by Henry V at the battle of Agincourt. It is set in a cross at the front of the crown.

The Cullinan II diamond, a cushion shape of 317.40 carats, is set in the headband at the front of the crown. It is a magnificent stone of fine colour and clarity, about 45 x 41 mm. 

The Stuart sapphire is set in the band on the opposite side to the Cullinan II. It is a blue stone of 104 carats, with a drill hole at one end. It belonged to Charles II but was taken into exile by his successor, James II, and later bought and returned to the Crown Jewels in the early 19th century. 

The Imperial State Crown, courtesy of UK Parliament, Flickr (Creative Commons).

St Edward’s sapphire is displayed at the centre of the cross at the top of the crown. It is a cushion-shaped stone which is said to have been worn by King Edward the Confessor and found in his tomb in 1163. 

The Crown Jewels incorporate many large and impressive stones, some of which have been named and have recorded histories. They are of interest for their qualities as gemstones; their sizes, colours and internal features, and because of their inclusion in the royal collections. They have been fashioned in many countries and in many different centuries, and so illustrate a range of historic cutting styles, from medieval to modern. Their identities have been confirmed so that they represent a historically important collection and a national treasure. 

Their use as a central feature in the coronation and on other state occasions is a rare survival of the ceremonial use of jewels and gemstones, which has been so important in human history.

Main image: Westminster Abbey, London, courtesy of Aaron Bradley, Flickr (Creative Commons).

Rubies and sapphires are often treated to improve their colour and appearance, but what are these treatment methods, and how can gemmologists pinpoint them? Here, Gem-A Tutor Pat Daly FGA DGA talks us through some of the most common methods used for corundum. 

Work is carried out on nearly all gemstones before they are offered to consumers. At the least, crystals and crystal groups are trimmed and shaped, and most stones are cut and polished to make them suitable for use in jewellery. Stones in these conditions are regarded as untreated, but a high proportion are modified in other ways to make them more attractive. 

Corundum, which includes the gem varieties ruby and sapphire, is very often treated, and this is likely to have been the case for more than 1,000 years. Early treatments included dyeing and heating using charcoal fires and blowpipes. Since the 1970s, increasingly sophisticated treatment methods have been used to bring many otherwise unsaleable stones to the gem market, improving the supply of gem quality stones and making attractive, affordable stones available in commercial quantities. 

Rough corundum crystals from the Gem-A Archives

Heating can now be carried out at higher temperatures than is possible with traditional methods, chemical elements may be driven into stones, and their clarity may be improved. Those who handle gemstones must know how rubies and sapphires can be treated and the clues that may inform us that they have been carried out.

Corundum Treatments: Dye 

Dyes are used to add colour to low-quality corundum. Pigments suspended in oil or water are deposited in fractures and pits. Treatment is recognised by the concentration of colour in fractures and the staining of solvent-soaked swabs wiped across surfaces. In jewellery incorporating closed-back settings, coloured foil placed behind a stone usually shows some crumpling, which can be seen with a loupe. 

Corundum Treatments: Heat

Heat treatment can improve colour and transparency at temperatures ranging from about 800 to 1900°C. Temperatures less than about 1000 to 1100° tend to lighten blue colours. This may be desirable to remove a modifying colour from rubies or to lighten the colours of sapphires which are too dark. There may be few clues to this relatively low-temperature treatment, but iron staining in fractures may change colour from yellowish-brown to reddish-brown. 

Ruby with crystal and feather inclusions, photographed by Pat Daly.

Higher temperature treatment affects the appearance of crystal inclusions and feathers and may be easier to recognise. Colours are modified by the intensification or reduction of blue and yellow. Those colours may become more vivid, or they may be used, for example, to turn a pink stone into the more favoured pinkish-orange padparadscha colour.

Heat treatment modifies the condition of the elements iron and titanium, which can be present as impurities in corundum. Both may combine with oxygen to crystallize as oriented needle-like inclusions. When there are enough of them, they may cause a star effect, but they can also occur as patches which reduce the clarity of stones. Heating can dissolve them so that the elements are incorporated in the corundum, and clarity is improved. These two metals interact to produce the blue colour of corundum, so this feature may be improved simultaneously. 

A synthetic star sapphire, photographed by Pat Daly.

Evidence of the former presence of needles may remain as lines of tiny dot-like inclusions or of small colour patches along the directions of the inclusions. These features have been called dotted silk and cross-hatched colour zoning, respectively. Straight colour zoning, seen in most blue sapphires, becomes foggy looking, the sharp boundaries between blue and white zones becoming blurred as colouring elements diffuse short distances in response to the elevated temperatures. 

Angular colour zoning in sapphire, photographed by Pat Daly. 

Fractures often develop around other crystals, producing features called heat discs, and when temperatures reach about 1500°, previously transparent crystals may become whitish and translucent, taking on a “frosted” appearance. Feathers, thought to represent fractures partly healed during the growth of gemstones, undergo subtle changes, but experience is needed to interpret them correctly.

Heat treated sapphire with heat disc features, photographed by Pat Daly.

Corundum Treatments: Diffusion

Colouring elements can be diffused into white sapphires, which do not improve after heat treatment. Pre-cut stones are packed in aluminium oxide containing titanium and iron and heated at up to 1850°C for some days. Colouring elements penetrate a short distance beneath the surface. Therefore, the stones must be repolished, removing some colour from the facets. When seen against diffused lighting, ideally when immersed and viewed from the pavilion side, it is usually noticed that some facets are paler than others and that colour is stronger along facet edges. Colour diffusion of chromium produces pink to red, and nickel is used for yellow stones. 

Titanium may be diffused into cabochon cut stones to improve a star. Subsequent heating causes needle-like crystals to grow in three directions, and these reflect light to produce the optical effect. In most untreated star stones, needle-like crystals are seen easily with a loupe, or the straight zones in which they are concentrated are prominent features of the stone. Suspicion should be aroused when neither of these features is seen. Suitable heat treatment may improve a star without surface diffusion if there is enough titanium dissolved in a stone.

Needle like rutile inclusions in sapphire from the Gem-A Archives.

The element beryllium may be diffused further into corundum and affect the whole stone, producing a wide range of colours. The features noted above for diffusion-treated stones are not seen, and these stones may be hard to recognize, though evidence of high-temperature treatment is usually visible.

Corundum Treatments: Clarity

Heat-treating stones in contact with a flux, such as borax, may partly repair fractures. This treatment is routine for stones from Mong Hsu in Myanmar, and those from other localities may be improved by it. However, the resulting feathers are similar to natural ones; some experience is needed to separate them.

Glass-filled ruby with iridescence in direct light, photographed by Pat Daly.

Fractures in poor-quality corundum may be hidden by filling them with oil or glass. Glass-filled rubies from Mozambique are recognised by iridescence, seen in fractures at low viewing angles, and by a change of lustre when wider cracks intersect the surface. Fracture-filled stones are much less valuable than good-quality rubies, and standard workshop techniques may damage them, so it is important to identify them.

Glass-filled ruby from the Gem-A Archives.

Pale, heavily fractured corundum may be filled with glass, at least some of which is coloured by cobalt. When seen in diffused transmitted light, colour is concentrated in fractures, the stones look red through a Chelsea colour filter, and they may display a cobalt spectrum. They also show the same features as glass-filled rubies.

Corundum Treatments: Irradiation

Irradiation may produce an unstable yellow colour in sapphires. This treatment cannot be detected except by a fade test; some stones from a parcel are exposed to sunlight for some time. Naturally coloured sapphires may fade in intense artificial lighting, but the colour will usually intensify again if the stones are held in sunlight or ultraviolet.

The treatment of corundum to modify colour and/or clarity is widely practised and serves to bring stones to the jewellery trade, which could not be supplied just by using untreated stones. The improvement of gemstones by treatments is acceptable, so long as buyers are told that they have been carried out and of any issues connected with durability, such as colour fading or inability to withstand heat in workshops. 

Those in the gem and jewellery trades should keep abreast of developments in this area of gemmology, pay attention to any ways that treated stones may be identified, and consider sending doubtful stones to laboratories to confirm their status. 

Main image: A sapphire with abraded facet edges, photographed by Pat Daly. 

Inclusions in diamonds are typically considered a negative trait, especially where their commercial value in the jewellery trade is concerned. But, as Gem-A Tutor Pat Daly explains here, inclusions in diamonds can be a fascinating area of study for gemmologist. Let’s consider some of the ‘disruptions’ to a diamond’s carbon lattice and uncover more about what makes inclusions so interesting. 

When measured by value, diamonds are the most important gemstones in the jewellery trade. Their quality is assessed in terms of the 4Cs; clarity, colour, cut and carat weight. The ideal diamond to be set in jewellery has no internal feature that an expert can see at ten times magnification. Accordingly, feelings about inclusions in diamonds are largely negative, especially if they can be seen easily with a loupe. 

However, those who are interested in diamonds may find inclusions beautiful and intriguing in themselves and appreciate the information they give about their growth and the otherwise inaccessible regions of Earth from which they come. Insights may be gained into the Earth’s mantle, its composition, and the connection between it and the movement of continents and oceans by plate tectonics.

Diamonds in conglomerate matrix photographed by Henry Mesa.

Some inclusions reveal the treatment of diamonds to change their colours or to modify their inclusions. Others supply evidence which can be used to separate natural from synthetic stones. 

Common Inclusions: Diamond Cleavages 

The commonest inclusions are cleavages, known as feathers in the diamond trade, and the black mineral films which sometimes coat them. Diamond is a tough material, but when it breaks, it does so more readily along flat surfaces, in four directions which are parallel with octahedral crystal faces. They are not desirable inclusions, but they are useful to gemmologists. Convincing diamond simulants do not possess this property, so it proves the identity of some diamonds. Many cleavages are thought to occur during the rapid and violent ascent of the volcanic rocks, which bring diamonds from the depths to the Earth’s surface.

An included diamond from the Gem-A Archives, photographed by Henry Mesa.

Diamond Colour Zoning 

A common feature of brown and pink diamonds is straight colour zoning parallel with the crystal faces of the growing stones. A feature called graining, which might be described as a kind of zoning recognised by optical features other than colour, is probably related to it. When it is subjected to stress within the Earth, diamond, in common with other minerals, may change its shape without breaking. However, it does so in certain definite directions in the crystal, and traces of this distortion may be evident as colour zones or graining. 

Irradiated Diamonds 

Some stones of poor colour that have been irradiated or may have been heat-treated to change them to attractive colours also show colour zoning. One of the most striking types has a shape resembling an open umbrella around the culet. This is seen in some stones which were irradiated by electrons in a machine called a cyclotron. Other types of colour zoning may be seen in stones irradiated in the past, but modern treatments tend not to leave such evidence. 

Crystals of Minerals within Diamond 

Tiny, indeterminate inclusions may be grouped into geometric shapes. For example, inclusions which resemble minute sugar cubes are seen in some diamonds. 

Dark inclusions in a diamond photographed by Henry Mesa.

Crystals of minerals which grew before, or at the same time as the host diamond, may be preserved within polished stones. Recognizable crystals are rare, occurring in about 1% of diamonds, but they tend to be eye-catching, and they can be very attractive. Despite their infrequency, it is easy to compile a list of 30 or more minerals by looking through recent articles in gemmological journals and standard works on gemstone inclusions. 

Diamond crystals, for example, may be swallowed up by larger stones and may be recognised by their octahedral forms. Where one of them intersects the surface of a polished stone, a raised feature called a naat might result from differential hardness effects when the crystal structures of the two diamonds are not in alignment.

Diamond Growth and Inclusions 

Most diamonds grow at about 100 to 250 Km below the surface of continents in two main rock types. It has been calculated that about two-thirds form in peridotite, a rock composed largely of olivine (of which the gem variety is peridot) and other minerals such as pyrope garnet and diopside. Transparent, white olivines are among the commonest crystal inclusions in diamonds. Chromium is a noteworthy minor chemical constituent of peridotite. It causes the bright red colour of pyrope and the bright green of diopside inclusions, indicating that diamonds formed in this rock type.

Diamond in conglomerate matrix, photographed by Henry Mesa.

The other type is eclogite, the high-temperature and pressure metamorphic equivalent of common ocean floor rocks. It can be a visually striking rock composed of green pyroxene and red garnet. Pyroxenes belong to a group of common rock-forming minerals, some of which are familiar to gemmologists. The one in eclogite is intermediate between jadeite and diopside. The garnet is intermediate between pyrope, almandine and grossular. Chromium is less abundant in eclogite than peridotite, and the colours of these crystals incline towards orange in the garnets and greyish green in the pyroxene, in contrast to the bright colours of those materials in stones from peridotites. 

Blue crystals of kyanite and brownish-to-black rutile inclusions may also be found in diamonds from eclogite.

Rare Diamonds 

More rarely, diamonds that grew at greater depths, between 400 and 800 Km, are brought to the surface. They are of great interest because they may be large stones of good colour and clarity. Some of their mineral inclusions are not found in rocks from higher levels in the Earth or, if they are, they are not seen in diamonds which grew at shallower depths. One of the commonest consists of mixtures of iron and nickel compounds, leading researchers to suggest that diamonds grew from liquids incorporating these molten metals. 

Removing and Adding Inclusions in Diamonds

Dark inclusions may be bleached by using a laser to burn a hole into them or to heat and expand them so that a crack opens to the surface of the stone. In both cases, strong chemicals can then be used to bleach them. The channels along which they are introduced supply evidence of the treatment. Cracks may be disguised by injecting them with glass. Bubbles and iridescence at low viewing angles reveal these fracture fillings. 

Fracture-filled treated diamond with a characteristic ‘colour flash’ from the Gem-A Archives.

Synthetic diamonds sometimes contain useful inclusions. For example, those grown at high temperatures and pressures in a nickel-iron flux may enclose some of it. It may be recognisable and, if large enough, it can make the diamond magnetic; this property is rarely found in natural stones. 

A laser drilled and fracture filled treated diamond with colour flashes and entry holes, from the Gem-A Archives. 

Manufacturers may laser-engrave the girdles of their synthetic diamonds, and one has even induced inclusions to mark them. For example, De Beers has engraved a logo beneath the table facets of its laboratory-grown diamonds in its Lightbox range.

Inclusions in diamonds are unwelcome from a commercial point of view but may be extremely useful in separating natural, treated and synthetic stones. In addition, they may serve as distinguishing features for individual stones, supply evidence of the conditions in which they grew, and some are welcome features to the gemmologists who are privileged to see them.