Foiling is a way of using tinted and silvered copper sheets to enhance the back of gemstones. The gemstone jewelry of the early Georgian era prior to 1800, was typified by it’s use of foiling. Even though the Georgians had already developed the open back mounting for gems, it was very rarely used until 1800 when à jour settings started to become popular. (À jour literally means in French ‘to the day’ and is loved because it allows the light to shine through a stone.) As we have developed the mathematics and the technology to properly cut and mount gemstones, foiling gemstones has become a redundant art-form. Although used in other eras, foiled gemstones have come to be seen as a signature element in early Georgian jewelry and is one of the signs to look for when evaluating the age of a piece.
Foiling gems produces a more intense, rich color and enables diamonds to twinkle in the candlelight; before the advent of electric lighting this was particularly desirable. Foiling acts as a light reflector. Quality gemstones were in less abundant supply in times past; foiling was an excellent way of transforming less than high quality stones into more desirable ones and also for matching stones as the foiling was also a coloring agent. It was also a way of creating a stronger, more noticeable look, suitable for aristocracy and officials. Foiling does tend to tarnish with time so unfortunately we rarely see the original full beauty of very old foiled gemstone jewelry unless it has been restored.
Other materials apart from metal sheets were also used to foil the back of gemstones. These included: peacock feathers, butterfly wings, colored silk thread and engraved metallic foils. Glass and paste glass could also be foiled.
“The possibility of temporarily masking the color of yellow diamonds has, in recent years, frequently led to fraud,” Max Bauer. c. 1890.
Unfortunately, less honest jewelers did often use foils to fool consumers into believing that gemstones were something they were not. For example, a green tinted foil back could be used to make a peridot a deeper shade of green and convince the purchaser that it was an emerald. It is for this reason that nowadays foiling gemstones is generally considered fraudulent unless there is disclosure. The 1974 edition of Shipley’s dictionary of gems and gemology writes that foiling came in three categories, and the last two of these were fraudulent. These were: genuine foil backs in order to improve the performance of a gemstone; false foil backs in order to give a different color to a gemstone so to mimic another and imitation foil backs which were the same as a false foil back, but applied to glass. By 1920, the art of foiling had completely gone out of favor because of the association with fraud. Nowadays, there are just a few specialists who use the art for restoration work.
What I find interesting about this is how attitudes have really changed; the contemporary mind cares about the objective value of a gemstone whereas in days gone by the apparent beauty of the stone was all that really mattered. This really comes down to the ‘purpose’ behind jewelry; in the Georgian era jewelry was often very much about displays of grandeur and wealth. In other words, all about external appearances. In the modern era, we very much like to know that something is not a fake, even if it appears exactly the same, we are concerned with truth and objective value. With this in mind, other ways of treating gemstones to be aware of include ‘tinting’ (this was when color was applied to the setting or directly to the gemstone), ‘waxing’, which increases transparency, ‘mirroring’, which involves putting a colorless mineral in the bezel which then acts a reflector and ‘coating’, which involves using similar substances to those used for optical lenses. ‘Coating’, is against the law unless there is full disclosure and is yet another thing for gemologists to be wary of.
Sources / further reading:
The popular jewelry motifs of the Georgian era were wonderful and varied; please look at my post ‘The Major Motifs of the Georgian Era’ to learn more.