Diamond Treatments PDF

DDG Ass #17 Diamond Treatments Clarity Treatments: - In the late 20th century, improved technologies brought many advances in diamond clarity treatments. Laser Drilling Treatment: -Since the early 1970s, diamond manufacturers have used laser drilling to disguise or eliminate dark inclusions. -In...

DDG Ass #17 Diamond Treatments Clarity Treatments: - In the late 20th century, improved technologies brought many advances in diamond clarity treatments. Laser Drilling Treatment: -Since the early 1970s, diamond manufacturers have used laser drilling to disguise or eliminate dark inclusions. -In this process, a carbon dioxide laser is used to drill a tiny tunnel, thinner than a human hair, by heating an area of the diamond until it evaporates. - laser drill-hole, provides access for acid to bleach or etch out the inclusion, or to vaporize it with the laser. This process lightens a dark inclusion Internal Laser Drilling: - Internal laser drilling works best on dark inclusions near the surface, and often leaves irregular channels within cleavages. - Instead of drilling a hole, a laser beam is focused on or near the targeted dark inclusion. The heat from the laser expands the inclusion, which creates enough stress on the diamond that existing cleavages expand and new cleavages may form around the inclusion creating channel for acid or bleach to lighten a dark inclusion Detecting LaserDrilling: - You might be able to detect a laser drill-hole with careful examination under 10x magnification, but higher magnification is often necessary. -A laser drill-hole opening is typically found on a crown facet. - Under magnification, a diamond with internal laser drilling may display a step- or worm-like series of tiny feathers or channels, typically black or white, with a sugary or frosted appearance. -A drill-hole is a permanent characteristic of a diamond, so all major gem labs grade laser-drilled stones and report a drill-hole as a clarity characteristic. Fracture Filling : - Fracture filling diamonds as a way to improve their apparent clarity was developed in the early 1980s. - all types are based on the same method: a molten glass substance is infused into a diamond’s fractures and cleavages to reduce their visibility. - A filling’s RI is closer to diamond’s than to that of the air it replaces, so the filled fracture is almost invisible to the casual observer. -An improvement in apparent clarity has greater impact on the marketability of larger diamonds and colored diamonds than that of smaller diamonds. - Diamonds treated by fracture filling show no evidence of weight gain after treatment -Filler can sometimes slightly lower a diamond’s color grade - Fillers can be damaged by common jewelry repair procedures. Detecting Fracture Filling: -A standard gemological microscope is sufficient to identify most fracture-filled diamonds. - The most obvious evidence of fracture filling is called the flash effect, which is a flash of changing color. -In darkfield lighting, the most common colors seen are orange, pink, and purple to violet. -In brightfield lighting, the most common colors seen range from bluish green to greenish yellow. - It’s important not to confuse the flash effect with the iridescence or orange staining from an iron-containing compound -Other signs of fracture filling include flattened gas bubbles, flow structure, and a crackled texture in the filled fracture -fracture fillings can be semipermanent, most gemological laboratories (including GIA) do not grade fracture- filled diamonds. They do, however, report the presence of fracture filling through a GIA Identification Report. Color Treatments: -The goal of all diamond color treatments is to create or remove color in lower-value diamonds to mimic natural diamond colors that are more valued. -Diamond value drops as color increases on the D-to-Z scale. - When enough color is present for the diamond to be considered a fancy color, value rises. - Diamonds chosen for color treatment are typically brown or in the light yellow range of the D-to-Z color scale. Irradiation: - Natural radiation in the ground makes diamonds nearby turn green. In the early 1900s, Sir William Crookes tried to duplicate nature’s process and turn diamonds green in the laboratory. - Exposure of a material to radiation is known as irradiation -Today the most widely used irradiation technique exposes diamonds to high-energy electrons with a linear accelerator, which accelerates atomic particles along a straight path. - Irradiation is typically performed after a diamond is cut and polished. - Irradiation is considered a permanent treatment for diamonds, meaning the color resulting from the treatment cannot revert to the diamond’s original color. -The color resulting from irradiation treatment varies based on starting material. Evolution of Irradiation Treatment: - Soon after World War II, atomic scientists invented the cyclotron for nuclear research. - The cyclotron was a large machine that accelerated atomic particles around a circular path. -Its introduction led to major developments in irradiation, and made laboratory irradiation of diamonds in commercial quantities possible. -Color zoning parallel to facet junctions is one sign of a cyclotron-irradiated diamond. If a brilliant-cut diamond is irradiated from the pavilion, the color zone is an umbrella-shaped area around the culet. -Scientists use half-life to measure the period of radioactivity in a material. Half-life is the amount of time required for half the radioactive atoms of a substance to become nonradioactive. -Once the first half decays in this way, the “clock” resets, this process continues until half of what’s left is an undetectable amount. -Half-life can vary from less than a second to billions of years. -The Geiger counter is a fairly simple and affordable instrument that can detect and measure moderate to high levels of radioactivity and is useful whne working with estate jewelry -In many countries, government agencies regulate the amount of radioactivity allowed in gemstones. Type 1 Starting Material : - When a diamond is irradiated, some carbon atoms are displaced from their normal crystal lattice positions, creating vacancies - These displaced carbon atoms are believed to be pushed into interstitial positions—typically uninhabited spaces in the regular framework of atoms. -In general, the vacancy absorbs energy in the red area of the visible light spectrum, and transmits energy in the blue to green area of the spectrum. This results in a blue to green bodycolor. -Type I diamonds have nitrogen atoms in place of some of the carbon atoms in the crystal lattice -The arrangement of these nitrogen atoms can cause absorption in the blue area of the visible spectrum, which can cause a yellow bodycolor. Type 2 Diamonds: -Type II diamonds have a negligible amount of nitrogen impurities. -Of type IIa and type IIb diamonds, irradiation is performed mostly on type IIa, both natural and lab- grown. - When type IIa diamonds are irradiated, a GR1 defect is created (the same defect as in type I diamonds). - Since there are no nitrogen atom impurities that result in a pre-existing yellow bodycolor, the only color center present is the vacancies—resulting in a pure blue bodycolor. Irradiation and Annealing : -Another way to change a diamond’s bodycolor is through annealing, a process of controlled heating and cooling. -After irradiation, annealing further modifies irradiated colors by allowing the vacancies and impurities to diffuse, or move, throughout the diamond crystal lattice and reorganize its color centers. -Unlike irradiation-only treatments, most colors produced by a combination of irradiation and annealing are considered stable when later exposed to heat Type 1a Start Material: - Type Ia diamonds are usually a mixture of type IaA and type IaB, written as type IaAB. -Irradiation and annealing of most type Ia diamonds will create a mixture of both the H3 and the H4 defects. transforming a type Ia irradiated blue-green diamond to either yellow, orangy yellow, yellow-green, or brown. Type 1b Start Material: - Type Ib diamonds are extremely rare in nature. Only those with a strong brown component are selected for treatment. -A nitrogen atom adjacent to a vacancy and can produce a pink bodycolor. The saturation of the pink depends on the strength of the bodycolor of the starting material and how long the stone was irradiated. Detecting Irradiation Treatment: - Most color treatments are difficult to detect, so diamonds you suspect of being treated to a gemological laboratory—advanced laboratory equipment provides the most reliable color origin identification. -Modern techniques create more evenly colored samples, you may sometimes see a color concentration around the culet or confined to the surface of a faceted diamond. -Whether the color of green diamonds is natural or artificial is sometimes impossible to determine, even with sophisticated laboratory tests -This is best detected using microscopic examination, diffused lighting, and/or immersion. The Deepedene Diamond Treated and Treated Again: - Gem historians believe that it came from a South African mine in 1890 and was originally cut by the I.J. Asscher Co. in Amsterdam. It appeared on the market as a light yellow 104.88-ct. cushion cut. -In the early 1900s, Pennsylvania socialite Helena Bok bought the diamond then it was sold to Harry Winston in 1954 -It was then irradiated turning it green and cut at the culet to 104.52 ct -Sold again in 1971 where it was yellow again High Pressure, High Heat (HPHT)Treatment: -Scientists found that using HPHT equipment at slightly different temperatures and pressures could be used to color treat diamonds, resulting in HPHT-treated diamonds, also known as HPHT-processed diamonds. -HPHT treatment can move and rearrange defects in a diamond’s crystal lattice. -the high temperatures and pressures create substantial etching and pitting on a diamond’s surface, all diamonds need repolishing after treatment. Type 1a Start Material : - HPHT treatment of type I diamonds causes existing vacancies and nitrogen atoms to diffuse throughout the diamond’s crystal structure, disassembling undesirable color centers and/or creating new color centers. -For example, HPHT treatment of type I diamonds can remove existing brown colors and create a yellow, orange, or yellow-green bodycolor. Type 2 Starting Material: - HPHT treatment of type IIa diamonds does not create new bodycolors; it releases the vacancy clusters that cause a brown bodycolor. Detecting High Pressure High Temperature Treatment - Identifying HPHT-treated diamonds involves advanced laboratory techniques such as photoluminescence spectroscopy. -One effect that can help you recognize HPHT-treated diamonds is the formation of graphite around a diamond’s mineral inclusions and feathers, or graphitization. -Etched or frosted naturals and fractures are also indicators. Multi-Step Treatments -Some treaters use a combination of HPHT processing, irradiation, and/or annealing to achieve the desired bodycolor. -Two examples are creating a pink color and creating a blue color, as highly saturated pink and blue diamonds are very rare in nature and highly valued. Multi-Step Treatment Blue: - The multistep treatment to create a blue bodycolor typically uses a type IIa brown diamond as a starting material. - First, the diamond is HPHT processed to remove the brown color, the diamond is irradiated, causing the GR1 defect—or vacancies—to form. These vacancies absorb energy in the red region of the visible light spectrum and transmit energy in the blue region,(without annealing) Low Pressure High temperature (LPHT)Treatment: - Low-pressure, high-temperature (LPHT) treatment works similarly to HPHT treatment by rearranging defects in the crystal lattice. -LPHT treatment works best to create black color in diamonds, by inducing large-scale graphitization within surface-reaching fractures. Coated Diamonds and Detection: - Coatings were one of the earliest methods of diamond color modification, and Primitive recipes for coating— such as a mixture of natural resins, oils, and pigments—have evolved along with the science of chemistry. -In the 1950s, modern coatings on diamonds were developed by the use of variations of compounds such as fluorides and later silica. -Carried out in a vacuum chamber, Coatings are typically applied as multiple layers with various trace elements (silver and gold, for example) to cause different colors. -Coatings are typically applied only to the pavilion of a cut diamond, but they are sometimes found on the crown. - These coatings are fairly durable but not permanent, and can be damaged by the heat and chemicals used during jewelry repairs -The signs of color coatings are often visible under simple 10x magnification. You’ll often see scratches and other surface features, such as areas with uncoated spots or patches. Color-Treated Diamonds and the Marketplace: -In the last 10 years, diamond treatments have become an increasingly important issue in the jewelry trade, making most gem professionals have been much more careful about detecting and disclosing treatments of all kinds. - All natural diamonds graded by GIA, whether treated by irradiation and/or HPHT processing, are disclosed and inscribed with “TREATED COLOR.” -Coated diamonds receive an identification report stating that the diamond’s color is due to coating.