This article will focus on the antique gemstone treatment of foiling, its widespread use by our ancestors and the reasons for its apparent decline in popularity. The first section of this article will define foiling and discuss the materials and techniques used in this gemstone treatment, with particular reference to Cellini’s ‘Treaties Of Benvenuto’; whilst the second half of this article shall explore the practical and social reasons for the use of the treatment and the reasons for its decline in popularity from the Georgian period (1714-1830) to the present day.
A treatment can be defined as any artificial alteration or enhancement of the optical or physical properties of a gemstone, excluding its cutting and polishing. Gemstones have been treated since our ancestors first decided they were of social and economic value to us, with Pliny making reference to treatments, such as the heating of carnelian, as far back as 1300BC. However here we will be focusing solely on the antique treatment of foiling, the first written account of which was given by Pliny in the first century AD, but can be dated back to Minoan times (2000-1600 BC).
[endif]--Foiling is a technique applied by goldsmiths to gemstones to “improve [their] optical performance” by “increase[ing] reflection from the back facets, thus making the stone appear more brilliant, or impart[ing] colour”. As a result of the foil “colourless stones are made more brilliant, pale ones deepened in colour, and dull ones become lustrous.” The process involves applying a thin backing/ sheet of foil with a metallic lustre either to the pavilion of a gemstone itself, or to a closed back collet, where the stone would be set with the pavilion (base) of the stone concealed, in order to hide the foil-backing and protect the foil, which was fragile and prone to decay.
[endif]--As foiling is such an ancient treatment it is hard to find comprehensive descriptions of the processes and materials used to foil back gemstones, however there is a fairly detailed account of the process, and how to make foils, in chapter VII of Cellini’s Treaties on Goldsmithing and Sculpture. Here Cellini sets out the recipes for four types of foil: (i) common (yellow) foil (ii) red foil (iii) blue foil and (iv) green foil; all of which contain the three metals gold, silver and copper at varying ratios. However, these recipes may have been altered or adapted since Cellini’s writing as the only modern-day mention of the recipe found states that it is commonly made with mercury and tin. Nonetheless the technique appears to have stayed the same and Cellini talks of melting the copper first, before adding the other precious metals to the molten solution, before cooling the foil and proceeding to flatten and scrape it down until it is thin enough to use, whereupon you must “blanch, clean and polish with tartar, salt and water…then wash in clear water, rub clean with a rag lightly, and then scrub it on a big copper tube that must be very clean and shining”. This foil would then be applied to the setting “with care…in a rim just deep enough for safety and not too deep to hide any appreciable part of the jewel”, whilst giving maximum colour and size to the stone.
Great care must be taken when selecting the right foil for your
gemstone. The choice of foil is akin to picking the right colour paint for a room: choose a colour too dark and the entire room seems to close in and become smaller, but choose the right colour and suddently the room appears bigger and more vibrant. It is with this concept in mind that Cellini advises that if we are to foil a stone, such as a ruby, “we must provide ourselves with four or five ruby foils” and carefully try each behind the stone until just the right affect is achieved. Here it is the subjective opinion of the setter as to which foil is to be used and carefully cut to compliment the stone’s colour and cut.
The majority of stones that were to be subjected to this treatment were cheap stones, dark and lifeless, usually cabochons[i] of garnet or corundum[ii]. However it is a common misconception that this was a technique applied solely to poor quality stones; a fallacy displaced by Cellini who writes of a set of buttons he was commissioned to produce for Pope Clement, which supported a large central, claw set, diamond; surrounded by “two large ballas rubies and two big sapphires, [which were] splendid stones, and four emeralds of goodly size”, all of which were foil backed. Thus it is clear that the art of foiling was, by Cellini’s own admission, applied to good quality stones and important commissions, as whom in 16th century Italy is more honoured than the Pope himself.
The coloured stones used by Cellini, much like the majority of others, were most likely foiled to enhance their colour, however it was not only coloured gemstones that were foiled; diamond, the king of gemstones, was often also foiled with a rich silvery foil to give the illusion of increased brilliance[iii]. Indeed, despite the central diamond in Cellini’s commission being claw set, it was in fact advised to him by some jewellery to “tint the whole base of the stone and the back facets”. From this it is clear that foiling was a practiced and accepted technique, which aesthetic effect of deepening the colour and increasing the brilliance of gemstones was highly coveted; however we must explore the wider historical reasoning behind the wide use of this treatment on gemstones, and the catalyst for its decline in popularity.
However, the Victorian era (1837- 1901) began to see the decline of the popularity of foils; partially due to the advancement in lapidary and diamond manufacture,[v] as well as the introduction of the claw and gypsy settings, which left foiled jewellery somewhat unnecessary and out of vogue.
The main gemstone cuts used in Georgian times were: the rose cut, table cut and old mine cut; which, whilst exploiting the colour of the gemstones and the high adamantine lustre[vi] of the diamond, did not give maximum brilliance or fire[vii] to the stones, which was compensated for by the extensive use of foils. However, during the Victorian period there were a number of advances in lapidary, leading to the introduction of the old European cut and eventually to the development of the modern day brilliant cut, which became popular in 1919. These more advanced gemstone cuts exploited science to allow for greater reflection and refraction within the stones meaning that it was no longer necessary to use foils to increase the optical performance of the stone.
The Victorian era also saw a transformation in the setting of gemstones into jewellery, as “settings were opened up in the back, and stones…enhanced in brilliance by being set in claws and prongs being held by beads of metal”; these were of a great contrast to their Georgian predecessors, who championed closed back and rub over settings whilst utilising foils to enhance the brilliance of their gemstones. Thus the change in fashion and the development of a more sophisticated style of stone setting seen in the Victorian period undoubtedly led somewhat to the decrease in popularity of the foil backed gemstone.
However, today foil-backed stones have once again become a highly desired commodity and authentic Georgian jewellery has become an investment as sound as any bond; thus it must be questioned why there has not been a revival in the foiling technique. Of course there are those that do still practice the art of foiling, such as Larkspur & Hawk, a modern-day company based in New York. However, the art of foiling has on the whole been lost, despite the high demand for the antique pieces. The primary reasons seem, much like the historical downfall of the foiling treatment, to lie in practical reasons: cost and fragility. As noted by Larkspur & Hawk themselves, the foiling process, much like any authentic antique processes, is one that is lengthy and costly taking “a skilled jeweller a great deal of time and precision to carefully create a foil backing, custom cut for each setting”. Thus, in a society today where commissioned jewellery is rare, it would not be economically viable to mass-produce foil backed jewellery.
A second practical reason that may be behind the decreased use of foiled gemstones in jewellery is the delicacy of the foil-backed pieces. The foils placed behind the stones are often fragile and have a tendency to wear over time, as “moisture can damage foil and make the stone ‘dead’, loosing its brilliance”. As water gets in behind the stone and settles between the foil and the gemstone itself it is unable to escape, with the liquid eventually evaporating as a result of the wearer’s body heat, which can cause the stone to have a cloudy appearance. To remedy this the stone must be taken out and cleaned and the foil replaced, which is a costly and inconvenient process. This may not have been such an issue to our grand ancestors, whose housework was most likely limited, however it is a significant disadvantage in today’s society where a ring could be tarnished even in the simple process of washing your hands.
There are also a number of social arguments for the decline in foil-backed gemstones, the first of which lies in the idea of forgery. Although we have seen that reputable jewellers used foiling for important commissions, there were some goldsmiths who used the treatment to quite literally ‘foil’ their customers, making low quality stones appear of a greater value. This concern of treatments deceiving customers was clearly paramount from an early point in history as, interestingly, the tinting of coloured gemstones was in fact illegal during Cellini’s time, although curiously the tinting of diamonds was not. Although these laws did not stretch to the foiling of gemstones they do demonstrate a social concern for gemstone treatments; a social concern which was related to foiled gemstones by Shipley in his 1974 dictionary of gems and gemmology, where he separates foiled gemstones into three distinct categories:
1.Genuine foil backs: which improve the optical effects of a gemstone
2. False foil backs: that change the colour of the gemstone in order to simulate another
3.Imitation foil backs: where glass/ paste is foil backed to simulate another gemstone name="_ftnref24" title=""
However, this social concern for deception is prevalent across the entire of gemmology, not isolated to the foiling of gemstones, but to treatments themselves; and because this is an issue so generalised to all gemstones and treatments it is fairly unlikely that the demise of foil backed gemstones was purely due to false or imitation foil backs entering the trade.
The final argument for the near extinction of foil-backed gemstones in modern jewellery is that today our gemstone market has been flooded with good quality gemstones at relatively affordable prices, thus economical need for foil backed stones has been replaced. This argument, however, is only prevalent to those foil backed gemstones that fall into Shipley’s latter two categories, whose purpose is to imitate more expensive stones. Regardless, it is a strong possibility that the expansion of the gemstone market did, in part, contribute to the decrease in the use of the foiling treatment; indeed today foil backed gemstones are highly prized, fetching astronomical prices for the raw materials they offer, and thus the economical motive behind them may indeed have become obsolete.
Notwithstanding the obvious decline in the popularity of the use of foils, it is still imperative that we identify them because, as discussed, although foil-backed gems/ paste can today have value, even when they fall into Shipley’s latter categories, using foils is still a treatment and must be identified and disclosed to buyers.
The first factor to consider in determining whether you are handling a foil backed stone is the age of the piece. As discussed, foil backed stones are normally found in antique pieces, and are not commonplace in modern day jewellery; as a result the age of the piece must be taken into account. If you are dealing with an antique piece then it is far more likely your stone has been treated in such a way.
In terms of gemmological testing the most important tools in a gemmologist’s arsenal when identifying a foil-backed gemstone are the unaided eye and the loupe. Firstly, with the unaided eye you may be able to see that the colour of the stone is concentrated at the base as you look through the side of the stone.
The unaided eye should also see a metallic lustre coming through the table/crown of stone, which comes from the metallic foil backing and is at odds to the general surface lustre of the stone. Another characteristic, which proves you are looking at a foil-backed gemstone, is discolouration or crumpling of the foil behind the stone, which may be seen through the table of the stone. However, this may be difficult to see and it is advisable to use a 10x loupe to thoroughly check the stone’s setting.
Once we have discovered whether the stone is treated we must decipher the identity of the gemstone itself; and in order to do this we once again turn to the 10x loupe. As foil-backed stones are usually set in closed back collets many gemmological instruments, such as the polariscope and dichroscope, which rely on the passing of light through the stone, are of little use. However the spectroscope and refractometer may be used to determine the identify of the stone in question, as they rely upon light reflecting inside of the stone and not passing through it, these must be used with caution as the light used may reflect off the foil instead of the stone and give false readings. The same caution must be applied with the Chelsea Colour Filter (CCF). Because of the limitations presented by the closed back setting, the loupe is essential in identifying the gemstone in question, and should be used to inspect the surface of the gemstone, looking at the lustre and any other surface markings, as well as the interior of the stone, searching for any diagnostic inclusions, such as bubbles in paste stones. Overall it is clear that, whilst foiling gemstones is an antique treatment that has indeed diminished in popularity in recent years, jewellery with foil treated gemstones increased dramatically in value and thus is important to be able to identify.
In conclusion, there is no doubt that foil backed gemstones have been revered throughout history and, as with any material object, fluctuated in and out of vogue, with their decline in popularity seemingly rooted in a number of practical and social issues; including advances in lapidary techniques, as well as the art of foiling becoming un-economically viable and somewhat impractical in twenty first century life. Nonetheless, it remains important that we can identify them as the rich colours of foil backed jewellery and their provenance mean those pieces that remain are once again highly sought after, and with fewer pieces enduring the test of time they will continue to be desired for centuries to come.
A massive thank you to: Dearrosewithlove, Auld_gems and shinyhappylily who all provided me with photographs of their own beautiful collection for this project! And a massive thank you to everyone else who sent me photographs and information that wasn't included.
 “The Early History of Gemstone Treatments”, Kurt Nassau, Gems and Gemology, Spring 1984: Ball 1950
 “Antique Paste Jewellery”, M. Lewis, Faber & Faber, 1970 pg.72
 Cellini, op. cit. pg. 28
 Cellini, op. cit. pg. 29
 “A History of Jewellery, 1100-1870”, Joan Evans, Faber & Faber, 1970, page 145
 Cellini opt. cit. pg 24
 Cellini opt. cit.
 Cellini opt. cit. pg. 30
 Cellini opt. cit. pg. 29
 “Antique Jewelry, a practical & passionate guide”, R. L. Goldemberg, iUniverse.com, 2000, pg. 64
 Gems and gemology, the early history of gemstone treatments, spring 1984, Kurt Nassau
 Shipley, Robert M., Dictionary of gems and gemology, 6th edition, 1974
[i] A cabochon is a gemstone that has been cut and polished, but not faceted.
[ii] Corundum is a variety of gemstone, which includes Sapphire’s and Rubies.
[iii] Brilliance is the white light that is reflected from the inside of the stone and returned to your eye
[iv] Lapidary is the art of cutting and polishing gemstones
[v] Diamond manufacture is the art of cutting and polishing diamonds.
[vi] Lustre is the quantity and quality of light returned to you by the surface of a gemstone
[vii] Fire is the splitting of white light into all components of the visible light spectrum, and therefore all of its spectral colours, by a gemstone.