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Home > Diamond News Center > Features > Articles > Diamonds, Gems and Jewelry

Clarity Treatments in Diamonds: Deep Boiling and Fracture Filling


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 Yehuda Yakar, GG GIA, Chief Gemologist at GCI

The methods for treating the clarity of diamonds improve the appearance of the diamonds but can cause problems. In this second article of a 2 part series, we will give a real example to explain this.

In 1997, a customer purchased a round diamond from the American chain of jewelry stores Almod Diamonds. It was reported that the diamond was 1.02 carats, its color was E and its clarity was SI2.

At that time, the Federal Trade Commission (FTC) laws did not require one to disclose laser treatments and therefore the customer was not informed about the laser drilling that the diamond underwent. After the diamond was purchased, she sent it to be appraised privately for insurance reasons. The appraiser instantly noticed the laser drilling. The shocked customer demanded that she receive her money back. Almod Diamonds contended that the FTC guide did not require them to disclose laser drilling and therefore they are not obligated to cancel the purchase. The customer was not satisfied with this answer and she turned to the FTC, the Consumer Protection Authorities in New York and other bodies. In the end, Almod Diamonds relented and gave the customer her money back.

This story is an excellent example of using the FTC rules for protection. Even though Almod Diamonds was protected from punishment by the FTC, it received bad publicity. Its image was damaged and it was publicly shamed.

After a number of similar stories, and in light of the international diamond organizations fearing a collapse in the public trust for the diamond industry, instructions were published that required the disclosure of all enhancement treatments, and sanctions were determined (large fines and in some cases expulsion from the bourse) for those who would break this obligation. These instructions apply to everyone working in the industry. This occurred with the understanding that full disclosure of treatments is not only an ethical issue, but also a legal and moral one.

Deep Boiling

polish diamond-Israel Diamond Institute
Israel Diamond Institute  Enlarge

Deep boiling diamonds is a process whose aim is to remove, distance, metabolize and whiten dark stains that are found in the stones and which have access to an external facet. Deep boiling metabolizes the filling material, as well, and returns the stone to its pre-filling state. This action is not considered a treatment and does not need to be reported.

Steps in the Process

In the deep boiling process, the diamond is inserted into a special tool made of the element tantalum and containing hydrochloric acid. Tantalum is a grey-blue colored metal that is especially resistant to corrosion and conducts electricity and heat very well. The process itself takes place at temperatures of 300 degrees Celsius, using pressure, and can last an entire night.

Fracture Filling

If a diamond has a fracture that does not reach the surface, the air in the fracture obstructs the passage of light inside the diamond, and turns the fracture into a reflective surface, making it easily visible. The fracture becomes shiny and it stands out to the observer.

The first treatment to fill fractures in diamonds became known in the 1980s. Since then, many manufacturers have begun to produce fracture filling substances. The exact ingredients of the filling substance changes from manufacturer to manufacturer, but its main component is molten glass. Originally, a glassy substance mixed with bromides were used. Because the material had a tendency to change color to grey when it was exposed to sunlight, it was replaced by other silicon-based materials. The filling substance has a refraction index that is closer to that of diamond than the air that it replaces, and therefore it turns the filled crack to nearly invisible to the naked eye. If the crack does not reach the surface, a small opening is drilled with a laser to insert the filling substance. Today, filling fractures has become a part of the industry. More diamonds undergo this treatment than other treatments such as exposure to radiation, lacquering, heat or pressure.


1. Diamond that in the past would have not been considered for their beauty now become attractive and accessible to a wider range of clients, thanks to the treatment. In this way, for example, improving the clarity vastly improves the ability to market large diamonds.

2. Cracks can also be filled with very small diamonds. However, because of the cost of the treatment, most diamonds that have undergone filling are heavier than one carat.


1. The process is reversible. Deep boiling or overheating return it to its original state

2. There is a possibility of a small reduction in the color of the diamond

3. The fillings can be damaged when the jewelry is repaired, as this may involve heating caused by an additional cut or the use of a burner or polisher

4. Over time, repeated cleanings can damage the fracture fillings, especially when using steam, acid, or an ultrasonic machine

5. Extended exposure to ultra-violet radiation, even sunshine, is likely to change the color of the filling that will take on a cloudy appearance over time

The filling can be replaced if it melts out, but if it turns dark, it can no longer be turned back to transparent. The only solution is to remove it and exchange it with new filling material.

Steps in the Process

1. The diamonds go through a cleaning process and are put inside a special oven

2. After the glass / glass powder has melted, it is used to fill the crack in the diamond, under high temperatures and high pressures

3. A special kind of slow cooling

4. Cleaning the diamond table until the desired effect is achieved


The ability to identify fracture-filled diamonds is necessary, especially because of the risk that filling can go bad when a piece of jewelry is cleaned or repaired. Fracture filling can be identified in these ways:

1. The most typical way to identify is with a flash effect that changes colors and is visible under appropriate lighting and magnification. The flash effect is created by a light ray that reflects as a result of the glass filling not equaling the refraction index of the diamond for the entire light spectrum

2. In order to observe the phenomenon, one must gaze at the crack and move the diamond back and forth at the same time. The color of the flash will change while the stone moves, and the background will change from dark to light

3. Fiber-optic lighting enhances flash effects

4. A diamond that has filling may contain gas bubbles which look like pin points. The bubbles are trapped in the crack or in the filling substance itself

5. Diamonds with filling can develop a cracked texture

When these phenomena are viewed under magnification, it is obvious that they are not part of the original internal structure of the diamond. Therefore, it is important to always ascertain that that the diamond was checked from various angles.

Fair Trade

Some laboratories do not document diamonds that have undergone fracture filling treatments in light of an IDC decision, which requires members of all diamond bourses and members of all diamond manufacturing associations to forbid gemological documentation for stones that have undergone reversible enhancement treatment. As per the obligation to disclose, some of the laboratories will grade the diamonds as they appear after treatment and note that the clarity was enhanced.


According to the rules of the large organizations in the diamond industry, the obligation to disclose treatments is true for all aspects of the industry, beginning with the manufacturer, to the trader, to the gemological lab, and up to the jewelry retailer. The labs must note the fact that a treatment was conducted in their grading reports and certificates.

The use of forms that give full disclosure of diamond enhancement treatments are very important to the diamond trader, so that he can at any time prove that he gave the customer full disclosure about the purchase, and that he supplied him with paperwork that require the evaluation of a gemology lab, price appraisal and a description of the stone on the receipt. The consumer must retain copies of all these forms.

If the consumer wants to be completely certain regarding anything to do with the presence of filling substances in the diamonds in his possession, or anything to do with enhancement and other clarity treatments, he must send it to a gemology lab for identification.

Every diamond that is sent for identification at a serious gemology lab is analyzed to check if it is real or synthetic, if it has a laser drilling or fracture filling, if it underwent radiation, if it was exposed to high pressures and high temperatures, and if it went through a CVD process, so the client receives all the relevant information about the diamond being analyzed.

There are laboratories that do not issue gemology certificates to diamonds that went through processes that are not permanent, such as lacquering and fracture filling, but they do supply certificates to diamonds that underwent laser drilling, radiation or HPHT processes, because these are permanent processes.

This article originally appeared in the HaYahalom magazine issue 205

By: Yehuda Yakar, GG GIA, Chief Gemologist at GCI
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