Gemstone Radiation: Enhancing Colors, Safely

Gemstone radiation is a common but little understood technique for altering colors. In this comprehensive blog post, we'll explore how it works and what gems usually receive this treatment.

Most gems on the market today receive various treatments to change their natural colors and create more desirable, salable products. Radiation and heating are the most common treatments, used alone or sometimes in combination with other enhancements. Although both treatments are common, radiation generates fear while heat carries little stigma.

Is Gemstone Radiation Safe?

The idea of exposing precious gemstones to radiation can understandably raise concerns about safety. However, when done properly by trained professionals, gemstone radiation treatment is a safe and widely-used technique in the jewelry industry.

What is Radiation?

Radiation comes in two main forms: electromagnetic radiation and particulate radiation.

Electromagnetic Radiation

Electromagnetic radiation includes visible light, X-rays, and gamma rays. These high-energy waves can interact with the electrons in a gemstone's crystal structure, leading to the formation of color centers that alter the stone's appearance.

Particulate Radiation

Particulate radiation consists of subatomic particles like electrons, protons, and neutrons. When these particles collide with a gemstone, they can also displace electrons and create color centers.

The Physical Effects of Radiation

To understand how radiation affects gemstones, we need to look at the underlying cause of color in these materials. Gemstone color arises from the way electrons in the crystal structure absorb and interact with light.

What Causes Gemstone Color?

Materials are colored because they absorb light. This occurs because the electrons in a crystal can exist in a number of distinct energy levels. These energy levels depend on the material's structure.

Light Absorption

When a light photon comes along that matches the size of the gap between energy levels, the light is absorbed. The electrons jump up to the higher level. After a short time, they usually fall down to the lower level again, losing the surplus energy as heat. This allows the atom to absorb more light.

For example, if all the atoms in the crystal absorb blue light, then only the yellow and red light will pass through. Thus, the material will appear orange or yellow. Keep this in mind: gemstone color is complementary to the absorbed color. Rubies are red not because they absorb red light. They absorb blue and green light and allow red through.

Elements and Color

Two large groups of elements can absorb visible light: the transition metals and the rare earth or lanthanide series. These elements can color popular gem materials such as cubic zirconia and synthetic garnets.

Idiochromatic gems get their color from these elements and can consist wholly of a compound containing the element. Allochromatic gems may contain just a trace of these elements and get their color mainly through selective absorption.

Gemstone Radiation and Color

To understand why radiation produces color, think of the radioactive particle as simply an energetic projectile fired into a gemstone. Like any projectile, it will eventually hit something and do some damage. The radiation can pass into the bulk of many materials because most atoms contain mainly empty space.

Electron Holes and Color Centers

The radiation most commonly results in an electron knocked out of its position in the crystal. It then takes up residence near another atom and leaves a corresponding "hole" in the electronic structure at its original position. This forms an "electron hole pair."

What happens next depends largely on the particular gem material. Sometimes, the material has a surplus of electrons in its structure, so a surplus electron fills the hole quickly. In other cases, the material has too few electrons, so the ejected electron finds a new home. As a result, the hole remains a persistent object. Both the trapped electron and the trapped hole can lead to color in the crystal. They are called color centers.

What Happens to the Color?

Because the radiation enters the crystal randomly, it can produce a range of different color centers. Some electrons are trapped in shallow holes and can easily escape, leading to fading color. Others are trapped in deeper holes and produce more permanent color changes.

Practical Gemstone Radiation

Finding suitable radiation sources is an important consideration for gemstone producers. Using a lump of radioactive material is impractical, so they often turn to gamma ray sources from cobalt-60 or electron accelerators. These can be purchased for around $75,000 and up, making them a viable investment for major producers.

Smaller-scale producers usually contract the work to a commercial radiation facility. Neutron irradiation, which requires a nuclear reactor, must also be done at a specialized facility, often at a university or government lab.

Checking for Induced Radioactivity

After irradiation, it's crucial to check the gem material for any induced radioactivity. Samples irradiated with neutrons can remain radioactive for months, as the neutrons transmute some of the atoms into radioactive elements. Gamma and electron irradiation usually result in much lower levels of induced activity, if any.

Removing Unsightly Color Effects

Irradiated gems often show unpleasant black, brown, or opaque colors due to the formation of a wide range of color centers with different depths. To solve this problem, heat the samples to allow the shallower color centers to recombine, leaving a relatively clean population of deep, permanent color centers with a single color. Exposing the samples to strong light can also help remove any remaining fugitive colors.

Gemstone Radiation Examples

Radiation treatment is commonly used on a variety of gemstones to enhance or alter their natural colors. Some of the most well-known examples include:

Topaz

Colorless topaz can be turned blue through irradiation and heating. The radiation creates color centers that absorb yellow and green light, resulting in the desired blue hue.

Beryl

Irradiation can turn the normally colorless beryl into various shades of green, yellow, or pink, depending on the specific treatment.

Tourmaline

Radiation can enhance the natural color of tourmaline or even introduce new colors, such as a distinctive green hue.

Diamond

Diamonds can be turned various colors, including yellow, green, and blue, through radiation treatment. The color centers created by the radiation are responsible for these dramatic transformations.

In conclusion, gemstone radiation treatment is a fascinating and widely-used technique in the jewelry industry. By understanding the science behind it and the safety precautions involved, we can appreciate the remarkable ways in which radiation can be used to enhance the natural beauty of these precious stones.