corundum, treatments.6, gems

gems, spinel, spinel inclusions, dendrite inclusions

jade, jadeite, fei cui, Burma, gems

Jadeite may be white, pink, lilac, brown, red, orange, blue, black or many shades of green, and contains different trace elements as colouring agents. Of these trace elements, iron shows the highest concentration and its oxidation states of ferrous or ferric iron produce different colours. In white jadeite nearly all iron is present as ferric (trivalent) iron, while in black jadeite half is ferrous (divalent) and half ferric. In the leaf green jadeites the Fe2+ /Fe3+ ratio ranges from 0.1 to 0.2. The finest green Burmese jadeite, whose colour is caused by up to 0.3 per cent chromium, has been called Imperial jade' or 'emerald jade'. Contents of iron (up to 0.6% Fe) and nickel (0.04% Ni) can modify the rich chromium green of the jadeite. Lilac, mauve or lavender jade may contain manganese (up to 0.01% Mn), cobalt (up to 0.001% Co), chromium (up to 0.001% Cr) and iron (from 0.006 to 0.3% Fe).

pearls, gems

A proposed explanation for the initiation of natural pearl formation is developed from studies of molluscan shell growth, epithelial behaviour and the structure of pearls. The author challenges the familiar account in which a grain of sand enters between mantle and shell and becomes coated with nacre, arguing that the close anatomical relationship between these tissues makes passive entry improbable. Instead, pearl formation is attributed to local proliferation of shell-secreting epithelial cells, potentially following injury or an unidentified natural stimulus. The discussion first outlines shell construction: an outer organic covering, a prismatic calcium-carbonate layer commonly composed of calcite, and an inner nacreous layer of aragonite platelets. The organic protein material termed conchin forms a matrix surrounding the mineral components and limits their growth into individual crystals. Changes in the secretory products of epithelial cells are related to cellular age. In the proposed mechanism, interactions between the epithelium and underlying connective mantle tissue favour expansion as a single-cell layer rather than an irregular mass. Continued proliferation produces an indentation that deepens into the mantle and develops into an enclosing pearl sac. Under ideal conditions, this sac and its growing pearl approach a spherical form. The cells are described as secreting the same materials in the same general succession as shell formation: an initial organic centre, followed by prismatic calcite and aragonitic nacre, with thin organic films between mineral deposits. Pearls with relatively large organic centres are discussed in relation to the trade term “blue pearls” and their darker central appearance in radiographs. Deposition is not presented as uniformly continuous concentric layering; overlapping cap-like increments and locally variable epithelial activity can produce irregular structures visible along drill-hole walls, although some layers may envelop the whole pearl. The possible involvement of G-proteins in signalling epithelial proliferation is introduced as a hypothesis rather than a demonstrated trigger. Shell-attached blister pearls arising from local irritation are distinguished from the free pearls addressed by the proposed model. The author acknowledges that the account combines experimental observations with theoretical interpretation and that the initiating stimulus and several cellular processes remain unresolved. The paper therefore offers a tentative biological model intended to replace an oversimplified foreign-particle explanation, while calling for direct observation of the complete formation process.

corundum, treatments.6, gems

The visual identification of heat treatment in ruby and sapphire is reviewed through changes in ultraviolet fluorescence and the microscopic appearance of inclusions, illustrated by eight photomicrographs. Heating is used to improve clarity by dissolving rutile silk, modify or enhance colour, and sometimes develop asterism in titanium-rich material. Because treatment produces no appreciable changes in refractive index, birefringence, specific gravity, dichroism, or visible absorption spectra, examination of internal features provides the principal means of recognition. Ultraviolet responses offer supplementary evidence. The apricot fluorescence commonly observed in untreated yellow-orange, yellow, and colourless Sri Lankan sapphires is reduced or eliminated by heating. Some heated blue sapphires display patchy, chalky green fluorescence under short-wave ultraviolet light, potentially resembling Verneuil synthetic blue sapphire. In heated natural stones, however, this fluorescence is confined to colourless areas, while blue zones remain inert; the synthetic material is described as fluorescing evenly across its surface. Heated rubies may exhibit unusual patches of chalky white short-wave fluorescence in addition to their normal red response. Microscopic indicators include partial dissolution of rutile needles, thermal alteration of included crystals, and modification of secondary fluid inclusions. Long, continuous rutile needles oriented in the characteristic directions of corundum are presented as evidence of an untreated stone, although remnants of silk may survive heating. Unequal thermal expansion can produce roughly circular, glassy tension fractures around included crystals, sometimes with rims indicating incipient healing. Crystals may become white, rounded “snowballs”, develop surrounding zones of melted material, or form negative crystals containing colourless or brown glass. In rubies, these altered inclusions may occur within partially healed fractures. Heating can also remove reddish orange staining from secondary fluid inclusions and transform their tubular liquid channels into strings of droplets that follow the original pathways. Surface diffusion treatment is considered separately because its colour is concentrated in a shallow surface layer that may be removed by repolishing. Diagnostic features include stronger colour at the girdle and facet edges, unequal colour concentration between facets, and colour extending into surface-reaching fractures or around inclusions connected to them. These features are most readily examined by immersion in methylene iodide under a microscope with diffused illumination; a dark-field arrangement fitted with a diffuser can reveal many of the same characteristics when immersion is unavailable. The article emphasises practical recognition using ordinary gemmological magnification, ultraviolet examination, and immersion techniques.

corundum, synthetic corundum.7, gems

An unusual colour-change synthetic sapphire demonstrates that twin lamellae, although commonly associated with natural corundum, cannot independently establish natural origin. The specimen, examined at the GIA Gem Trade Laboratory’s West Coast facility in November 1994, was a transparent emerald-cut stone weighing 1.43 ct and measuring approximately 6.85 × 5.73 × 3.80 mm. It appeared bluish green under daylight-equivalent fluorescent illumination and pinkish purple under incandescent light. This behaviour resembled that of the vanadium-doped, flame-fusion synthetic sapphires frequently submitted to the laboratory, sometimes in the mistaken belief that they are natural or synthetic alexandrite. Such synthetic corundum is normally identified without difficulty by a vanadium-related absorption band near 474 nm and curved growth striae visible under magnification with darkfield illumination. In the reported specimen, initial binocular microscopic examination revealed neither solid mineral inclusions nor cavities such as gas bubbles or negative crystals. Instead, a conspicuous series of laminated twin planes was readily visible through the table facet. Although the author emphasises that twinning does not prove natural origin, its presence could have encouraged that interpretation because it is an uncommon feature in flame-fusion synthetic corundum. Continued examination from different directions resolved the apparent contradiction: observation through the pavilion facets revealed curved striae, establishing the stone’s synthetic origin. The note places this finding alongside earlier published accounts of polysynthetic twinning in Verneuil corundum and reviews other atypical internal features that can complicate identification. These include undissolved alumina, triangular cavities containing gas bubbles and needle-like inclusions. Their occurrence shows that synthetic corundum may contain features that differ from the familiar curved striae and rounded bubbles expected in routine examination. The principal diagnostic lesson is therefore methodological: an identification should not rest on the first inclusion or structural feature observed. All internal characteristics must be evaluated together, and the gemstone should be examined from several viewing angles before a conclusion is reached. In this case, the combination of unusual twinning with diagnostic curved growth striae illustrates the importance of a thorough microscopic investigation.

corundum, treatments.6, gems

corundum, quality.10, gems

Reviews conflicting accounts of the discovery and recovery of the Cheapside Hoard, a collection of approximately 340 jewellery items unearthed in London in 1912, and combines this historical investigation with descriptions of exceptional gemstones and workmanship. The hoard is interpreted as the stock of a Jacobean goldsmith, pawnbroker or dealer, buried under unknown circumstances in the early seventeenth century. Gosling compares museum catalogues, historical studies, newspaper tributes and recollections that disagree over the precise location, date, container and manner of recovery. Reports variously describe a decayed wooden box, a bucket, or jewels embedded in lumps of clay, while the absence of a direct account of the actual excavation prevents a definitive reconstruction. Central to the story is G.F. Lawrence, known as “Stony Jack”, whose relationships with building labourers enabled him to recover archaeological objects for London museums. Accounts portray him purchasing finds from workmen and receiving successive deliveries of clay-encrusted jewellery at his Wandsworth premises. The article highlights both his contribution to preserving the hoard and the unresolved details surrounding ownership, payments and Treasure Trove claims. Institutional disputes delayed agreement until 1916, when the collection was divided principally between the London and Guildhall museums, with smaller holdings elsewhere. Their later amalgamation reunited most of the material in the Museum of London. Gemmological notes describe a watch enclosed in Colombian emerald, identified by characteristic multiphase inclusions; a table-cut diamond estimated at three to four carats with a modified scissors-cut pavilion; and a hexagonal sapphire displaying rutile silk, pronounced growth zoning and an unusual combination of crown facets and a stepped pavilion. The sapphire’s appearance and setting are compared with those of the Stuart Sapphire. Amethyst and emerald grape pendants illustrate sophisticated lapidary methods, apparently involving intersecting annular drillings followed by removal of intervening material and rounding of the exposed ends. Gosling also considers how damp clay beneath a chalk cellar floor could explain decay of the container and dispersal of its contents. He concludes that the surviving uncertainties justify a new authoritative illustrated catalogue and consideration of further reunification of the collection, while recognising its importance as evidence of Elizabethan and Jacobean jewellery, gem cutting and material culture.

corundum, treatments.6, gems

gems, books on books, book collecting, gem books, bibliography

Norma Levarie’s The Art & History of Books, originally published in 1968 and reissued by Oak Knoll Press and the British Library in 1995 with a new foreword by Nicolas Barker, is an extensively illustrated survey of the development of the book as an artistic, intellectual, and material object. Rather than treating the history of printing solely as a sequence of technological innovations, Levarie examines the relationship between book design and the changing religious, political, economic, and cultural circumstances of the societies that produced books. The study ranges from the earliest surviving examples of written and illustrated books to twentieth-century publishing, considering the evolution of manuscript production, typography, illustration, page composition, and the aesthetic principles governing the relationship between text and image. Particular attention is given to the transformation from manuscript to printed book and the ways in which printers, artists, publishers, and patrons adapted established artistic conventions to new methods of reproduction. The introduction of movable-type printing in fifteenth-century Europe is considered within the broader history of bookmaking, emphasizing both its revolutionary consequences and its continuity with earlier manuscript traditions. Levarie examines the influence of Renaissance humanism, religious reform, expanding literacy, and changing patterns of patronage upon the appearance and production of books. The study follows the development of European printing through successive centuries, addressing the interaction between typography, illustration, decorative ornament, and the increasingly specialized professions associated with book production. Illustrated books receive particular emphasis, including the artistic possibilities offered by different reproductive techniques and the contributions of artists and designers to the visual character of printed works. The changing relationship between publisher, printer, illustrator, and reader is examined alongside improvements in printing technology and the emergence of new markets for books. The discussion extends beyond European printing to consider bookmaking traditions in other parts of the world, placing Western developments within a broader cultural and artistic context. One of the publication’s principal strengths is its extensive visual documentation, comprising 176 facsimile pages reproduced from books selected for their unusual beauty, historical significance, or distinctive design. Many examples were photographed specifically for the original publication, allowing readers to examine the arrangement of type, illustrations, margins, ornament, and other elements of page design. These reproductions are integral to the author’s argument that the history of the book cannot be understood independently of the physical and visual qualities of surviving examples. The volume itself demonstrates the principles under discussion through its carefully considered typography, page layout, and relationship between illustrations and explanatory text. The 1995 edition preserves the original study while adding Barker’s introductory perspective and an updated bibliography. Although the work is not specifically concerned with gemology, it provides valuable historical context for the study of early mineralogical, scientific, and gemological publications, particularly their typography, engraved illustrations, printing methods, and changing standards of book design. For bibliographers and collectors of historical gemological literature, the volume offers a useful framework for understanding the artistic and technological circumstances in which illustrated books were produced, as well as the importance of their physical characteristics in bibliographic description and historical interpretation.