By Nancy Attaway
Editor’s Note: This article is excerpted from “Back From the Dead: How to Resurrect Dead Gemstones,” a paper by Nancy Attaway and Stephen W. Attaway, Ph.D., which was published in the proceedings of the 2018 Santa Fe Symposium on Jewelry Manufacturing Technology.
When faced with a chipped or worn stone, many jewelers may instinctively guide their customers to replacement stone options, believing that it would be cheaper and easier to simply replace the damaged stone. But that might not always be the best option, especially if dealing with a gemstone that holds significant meaning for a customer.
Many damaged stones can be repaired. While small chips, scratches, and abrasions will reduce both a gem’s beauty and its value, repairing the stone can often restore the gem’s beauty and durability as well as renew its value, and all for less than the cost of a replacement stone. But there is a limit to what can be done.
In this paper, we examine the types of stone damage that can often be repaired as well as how to determine if the repairs make sense from an economic standpoint.
Assessing a gemstone’s damage is difficult. The first step in considering a repair involves a detailed study of the gemstone to understand what needs repairing. Start by evaluating the stone by looking closely at the facets through a jeweler’s loupe under good lighting. Check the stone from different perspectives by tilting it in your hand, as this can reveal inclusions not noted from the table facet. A loupe can also reveal damage such as scratches and chips. For a stone to be a candidate for repair, it must still be durable, and any damage should be near its surface. If the damage runs too deep, too much carat weight would be lost in the repair, so replacing the stone would be the better option.
If you have access to one, a gemstone microscope with back lighting can be used to check for internal flaws. Observing the stone within a refractive index-matching fluid will make internal cracks easier to spot. The top, bottom, and girdle areas should all be studied to understand what repairs are needed or possible. You can also contact a gem cutter for an assessment as to what is possible as well as to provide an estimate of the repair cost.
Now let’s take a look at some of the most common gemstone repair and re-cutting options.
In some gem repairs, only the table facet may need repolishing. Scratches and dings are usually found on a gem’s table facet after years of wear in a ring. The points or junctures where individual facets meet are easily damaged from wear. Figure 1 shows an example of facet junction wear. When this occurs, a gemstone may need only the table facet repolished, along with a few crown facets, to remove damage.
Repairs on table facets depend on what type of damage is present and how deep the damage runs into the crown. Damage to table facets can vary from slight scratches and small chips to deep furrows and long plowed fractures.
Fortunately, repolishing a gem’s table facet can sometimes be done without removing the stone from the setting. This requires the gem to sit high enough in its jewelry setting that the cutter can reach the table facet without damaging the metal that surrounds it.
For example, Figure 2 shows a ring with a gemstone held in place with Jett Sett in a large brass V-dopstick used for holding a stone. This configuration allows the cutter to repolish the table facet without the gem being removed from its setting, saving the customer money while also making the jeweler happy.
Damage to the table facet is often accompanied by small chips to the tiny decorative star facets that usually surround the table facet in most designs. Sometimes these star facets become completely obliterated from years of wear. The crowns of gems then appear so badly worn that they bear no resemblance to the beautiful faceted gems they once were.
Crown facets on very hard stones such as ruby and sapphire will also wear over time when set in rings. The photo on the left in Figure 3 depicts a ruby removed from its original ring setting, now affixed on a dopstick with epoxy, ready for repair. It shows the extreme wear inflicted on the ruby’s crown, which was so severely damaged that the original faceting pattern had been erased. It was possible to repolish the stone without changing the girdle outline, and the stone lost only three-tenths of a carat after repolishing.
A gem’s pavilion can be successfully re-cut to improve both brilliance and color in most cases, provided that the pavilion is deep enough for the gem to accommodate its proper cutting angles. Some carat weight may be lost during these re-cuts, but the re-cut gemstone can be placed into a higher-rated category that reflects an improved gem grade.
For example, Figure 4 shows the transition of a large aquamarine where the pavilion was re-cut to make the angle steeper. The windowing seen in the left photo was closed. The gem’s color became darker due to the longer path length of the light rays traveling through the stone. In addition, the stone lost only 7 carats in the process.
For this particular gem, a reverse engineering of the original cut was required. Figure 5 shows a reverse-engineered design for the pavilion recut: the example before re-cutting (left) and the design used for the re-cutting (right). (The designs were created using GemCad, a computer program re-cutting tool that can be used to design a new faceting pattern for an existing gemstone to improve sparkle.) The primary difference between the two designs is the angle of the facets near the culet. The new design incorporates culet facets with steeper angles that run nearly from girdle to culet.
When damage has been inflicted on the girdle of a gem, it will depend upon how far the damage reaches into the gem to determine if repairs are even possible. Simple adjustments by a cutter can fix many small chips while still allowing the gem to be reset in its ring. If the damage runs into the gem in such a way that the overall shape is no longer exactly symmetrical, then a bezel setting might be an optimal choice instead of a prong setting.
Girdles that come to a knife-edge are a nightmare to set in jewelry because they run the risk of chipping or napping during setting. Figure 6 shows an example of a knife-edge girdle.
Refaceting the stone to remove the knife-edge girdle should be considered if the stone is slated for a prong setting where the girdle edges will be visible. For gems slated for bezel settings, the girdle will not be visible and can be trimmed using hand tools at the bench. For example, Figure 7 shows the removal of a knife-edge girdle using an Edenta Ceragloss mounted diamond polisher.
The crowns of some gemstones can be-come too damaged to properly refacet. For example, a stone with a very flat crown may not have enough room for a faceted repair. Sentimental value often drives the decision to salvage a stone. One option for saving such stones is to buff-cut the crown so that it has the shape of a cabochon. The resulting gem will have a cabochon top and a faceted bottom. The conversion from a faceted top to a cabochon can usually be done while the stone is still in the mounting.
Re-cutting a gem into a new shape entirely may be another alternative, provided that the gem has a high enough value to warrant the labor and cost for a re-cut. A total re-cut implies that a gem’s original shape will be changed to an alternative shape with a new pavilion, girdle, and crown that will then require a new jewelry setting. The jeweler, cutter, and customer would need to agree upon how to proceed with creating something new from the old. This will be determined by how much of the original gem is left intact and what shape the remainder of the gem material may allow the cutter to render.
You shouldn’t expect a repaired stone to be an absolutely perfect gem. The primary goal is to restore the beauty and durability of the stone, not to produce an award-winning faceted gem. A trade-off exists between how much of the damage can be removed versus how much carat weight loss or geometry changes are allowed. The goal of a total re-cut stone should, however, be an absolutely perfect gem.
It’s important to note that carat weight will be lost in re-cutting. For example, the repolishing of a crown should result in as little as 1 percent carat weight lost. Re-cutting a full stone to transform it from one shape to another (such as a square into a round) can result in significant carat weight loss.
Not every gemstone will lend itself to repair or re-cutting. Let’s take a look at some of the situations where re-cutting a stone is either not economical or ill-advised.
Small stones under 4 mm in size will not be economical to re-cut unless the stone is very rare, such as an alexandrite, an unheated Burmese ruby, or a Yogo sapphire from Montana. Unless the small stone is sentimental or rare, replacement of the gem will typically be a less expensive alternative than re-cutting.
Gem rough can grow in such a way that internal flaws and residual stress are trapped inside the stone. These internal flaws, combined with residual stress and cleavage, make for a risky repair. For certain stones, such as emerald, there is always the risk of a complete stone loss due to running fractures. We heard from one cutter, who had repaired such an emerald, that the emerald catastrophically “snapped in half” the next day after re-cutting. Some inclusions can even develop overnight. We have also observed this problem in a few red tourmalines during the faceting process. The rough gem crystal in the faceting process appeared water clear in the beginning but developed a stress crack during polishing.
Fracture-filled gemstones and glass-filled stones typically cannot be repaired after being damaged. There is a risk of losing clarity and color due to the colored oils or resins used to enhance a stone, such as what is used for emeralds. The new glass-filled rubies are also typically not worth repairing, as they are not durable because the glass filling can dissolve in a jeweler’s pickle pot.
Gemstones that have been treated with surface coatings cannot be repaired when damaged. These need to be replaced since applying a coating often requires special equipment designed to treat batches of stones, making recoating a single stone un-economical. The surface coatings are merely micron-thin layers of color deposited on a gem. Once the stone is chipped, the surface coating is completely erased. Some diffusion treatments deposit thicker coatings on a gem’s surface, while other diffusion treatments may penetrate into the gem a short way. The recent diffusion treatments in sapphire to alter the gem’s color penetrate the entire stone, but the resulting color may be a bit off and not look natural.
Making a stone brighter will usually deepen the color. However, re-cutting for the brightest possible shape may cause the color in an already pale gem to lighten in hue. The light blue aquamarines, lavender amethysts, and pale citrines will return a dazzling light when properly re-cut, but their color may not be enhanced much at all due to the light taking a shorter path through the stone.
Colored gemstones of high value should always be considered for repair, but what about those stones of a lower value? How can you determine whether or not it makes financial sense to have a stone repaired?
The actual repolishing process for gem repair is quite tedious. The angle at which each facet was cut and where each facet lies on the gem must be located before the cutter can repolish it. Since all facets on each row were cut at certain angles by the original cutter, the cutter now rendering the repair must locate every facet and eliminate the damage by repolishing each one while keeping the original design in a balanced proportion.
Repairing a gemstone can sometimes take longer than the time used for cutting the original gem. The original cutter had the gem crystal rough and a cutting diagram as constraints. The repair cutter will not likely have access to the original cutting diagram. In some cases, the repair cutter will need to re-derive the angles and indexes for the damaged stone. This reverse engineering of the stone takes time and can add substantial cost to the repair.
Expect re-cutting costs for custom cuts to range from as low as $1.50 per carat to upward of $100 to $500 for a stone. Re-cutting a 5 mm round anthill garnet for $3 a carat is different from re-cutting a 3-carat $75,000 natural Burmese ruby. The price for cutting expensive goods is usually set by the piece. When the value of an expensive stone is above $10,000, a re-cutting charge on the order of 5 percent of the stone value may not be excessive, provided that the stone is going to be transformed into a gemstone worth even more. Custom-cut gemstones, such as a Barion style or Portuguese cut, will cost more to repair than a simple step cut done on the top and bottom.
Also, consider that jewelers will often add a multiplier to this re-cutting cost that raises the customer’s final repair cost even higher. And, if the stone must be removed from the setting, there are additional costs involved for unsetting and then resetting the stone, which can be significant.
Given the labor involved in re-cutting stones, is fixing a damaged stone worth the time and effort? It depends on the stone. If the repair costs would exceed the cost of replacing the stone then the damaged stone would not be worth fixing, barring any sentimental attachment to it by the customer. Ultimately, the jeweler should present the options for fixing the stone to the customer so they can decide whether or not repairing it makes financial (and emotional) sense.