How can i FOIL BACK a faceted gemstone?

Jewelry Discussion
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I have a piece where the design necessitates the back of the gemstone being closed and not exposed to any light. I can also see through most stones and its very unsightly. It has small prongs but is fully enclosed/wrapped from the girdle down. I am using standard round faceted gemstones. I was looking for a solution to get it more beautiful and keep me from being to see through the stone, and re-discovered georgian era foil backing.

What is the best way to apply the foil to my gemstone? Ie amethyst, pink topaz, tourmaline, etc…
I think this would look beautiful in the design and be a nice historical reference as well.

I’m finding a lot of information on them historically but next to none on applying the foil. Does anyone have any ideas?

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Foil backed stones are pretty common in costume jewelry. Foil backs though are really fragile and moisture can wreck them. That is the reason why the fell out of favor. Once electricity became common there was no need to enhance the reflectivity of set faceted gems. I would redesign so that the stones could shine and reflect with natural light.
Jo

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This sounds like a question for the folks at GIA. You might want to also touch base with some museums that have Georgian era jewelry in their collections. The museum staff up front might be able to answer your question but I am betting the conservators in the back will be able to either answer or point you to someone who can answer your question. If it were me, I would start with the British Museum.
Make sure to share what you find out! I have always wondered how this was done as well.

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It took me two clicks to find this very extensive article on foil backs, complete with references from Cellini to the present:

The author is a gemologist and proprietor of a gem antique business in London’s Hatton Garden District.

Let me add this as a gem cutter…if a faceted stone is well cut, you won’t see thru it when it is viewed face on…with low RI stones, even up to RI=1.76 (topaz and corundum are in this range) there is going to be the beginning of some windowing at about 10 to 15 degrees tilt off axis when the stone is viewed at the normal viewing distance for a ring. This occurs mostly because of what’s called the “head shadow effect”. Rays of light enter the gemstone perpendicular to the table around the head and are returned to the eye, but light rays blocked by the head and neck result in no light return, hence the window you see. Higher RI gems, esp. diamonds and CZ do not window, esp. in round stones or other symmetrical.
cuts.
Now all that said, many commercial gemstones are still cut with incorrect angles, which means they window even face up. There is often a collar of brilliance from the crown facets, but the table is completely dead. This occurs because commercial cutters belly the pavilion to add weight to the stone and sacrifice brilliance and best color to that end. This is so even tho’ we have now known about proper angles for cutting diamonds since Tolkowsky studied the SRB cut for diamonds in 1919 and since Long and Steele computed correct angles for hundreds of facet cuts for colored stones using Texas Instruments calculators in the 1980’s, colored stones could be cut to correct angles, too. There are now several computer programs that virtually cut stones and can show you animations of what properly cut stones look like…all of which reduces or eliminates the problems that require foil backs, which just don’t last forever.

As far as cabochons go, yes, you can often see thru them. If the stone is dark, it isn’t too much of an issue. Cabochons which are translucent reduce this problem, as you can’t see thru them completely and they seem to glow s light diffuses thru them. I have some aqua now that is too cloudy to facet, but I think it is going to make some killer cabs, even if these will not be highly valued.

I saw some discussion of using stainless steel rings with a mirror of stainless behind the cab stones on one of the old faceting forums…the idea being that the stainless would not tarnish much. I suppose you could use the newer tarnish resistant silver alloys…perhaps Pt would not tarnish much? Or read the link above about the Old World foiling techniques.

If anyone is interested in modern optimized facet designs, I am happy to discuss this. DM me. I have been faceting on and off since 1996 and have done more virtual cutting than cutting of real stones. Many faceters and facet designers use the same angles for a design in any species, claiming that you don’t really have to optimize for each type of stone, but I disagree and I optimize differently for lighter colored stones than darker colors and differently for tourmaline, say, vs rhodolite. I can see a difference in the light performance. If you know what to look for, you will, too. Beth apparently doesn’t like windows in stones, and neither do I. She hit the ball right down my alley. I may have some comparison stones to show soon. -royjohn

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Hi! Thank you. I did read that article but am struggling with the nitty-gritty of technique.

Thank you for the additional thoughts! This is helpful

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Hi! Unfortunately that is not an option- the stones are set into a closed, sculptural, 3 dimensional form. It’s something I’m paying more attention to while designing future pieces.

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I love this idea! Will do :slight_smile:

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I generally use small, thin, polished discs of fine silver behind stones that require the extra ‘flash’ behind them. FS because it tarnishes much more sloly than Sterl. However, if that doesn’t suit what you are looking for, I think the idea of stainless steel, polished to a mirror finish might be a good alternative. Here are some possibilities.
Google McMaster-Carr for stainelss steel washers:

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Linda,
Your reply about the stainless jogged my memory. Carlos Peixoto, from Brazil once talked about making stainless steel rings and shining up the stone seats for cabs mounted in the rings on one of our old faceting groups…Carlos was a member on here as late as 2021, and may still be around. He might be able to tell us what he did and how it worked. If this post doesn’t produce a reply from him, I’ll see if I can’t message him about this directly…-royjohn

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I forgot to mention that if you click on the images of McMaster Carr that I included in my post (above), they are URLs that will take you to the two possibilities that might suit your needs.
Linda Kaye-Moses

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You might also consider using a highly polished thin Argentium backing. Like fine silver, it is very slow to tarnish.

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When we put a highly polished surface beneath a stone we always use platinum. Eventually even argentium and fine silver will oxidize. Palladium would work as well.

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