Opals are admired for their mesmerizing play-of-color. However, these gemstones can develop a yellowish tint over time, diminishing their vibrant appearance. Understanding why this occurs and how to prevent it is important for preserving an opal’s beauty.
The Science Behind Opal Yellowing
Opal is composed of hydrated silica, with water content crucial to its optical properties and stability. If an opal loses this internal water, a process known as dehydration, it can lead to structural changes like cloudiness, “crazing” (fine cracks), or a yellowed appearance. This is especially true for hydrophane opals, which are naturally more porous and readily absorb or release water.
Hydrophane opals are highly absorbent. When these porous opals absorb substances like oils from skin, lotions, perfumes, or cleaning chemicals, impurities can become trapped within the stone. Over time, these absorbed substances can cause discoloration, often resulting in a persistent yellow or brownish tint.
While dehydration and impurity absorption are primary causes, subtle internal structural changes also play a role. Some opals contain trace elements that can oxidize over time, leading to a gradual shift in body color, including yellowing. This natural aging process is a slower cause of yellowing compared to water loss or external absorption.
Preventing Opal Discoloration
Preventing opal yellowing requires mindful care. Proper storage is important; keep opals away from direct heat, prolonged sunlight, and dry environments to prevent dehydration. For long-term storage, a slightly humid environment, like a sealed bag with a damp cotton ball (not touching the stone), helps maintain moisture. Store opals separately from other jewelry to prevent scratches.
Protecting opals from chemicals and oils is equally important, especially for porous varieties. Remove opal jewelry before washing hands, applying lotions, perfumes, or using household cleaning products. These substances can be absorbed, leading to discoloration or damage. Avoid oiling opals; oils do not hydrate the stone and can cause a greasy film or permanent yellowing.
When cleaning an opal, gentle methods are best. Solid opals can be cleaned with a soft, damp cloth and mild soap in warm water. Doublets and triplets should only be wiped with a damp cloth to avoid dissolving adhesive layers. Avoid harsh chemicals, bleach, and ultrasonic cleaners for all opals, as they can cause irreversible damage or cracking.
Addressing Yellowed Opals
If an opal has yellowed, remedies may be possible depending on the cause. For discoloration from surface impurities, a gentle cleaning with a soft cloth and distilled water might help. If hydrophane opals yellowed or became translucent from absorbing plain water, allowing them to air-dry naturally over days or weeks can often restore their color. Do not speed up drying with heat, as this can cause cracking.
For yellowing caused by absorbed oils or liquids in hydrophane opals, careful cleaning with specific solvents, such as acetone, may draw out substances. However, this is a delicate process with risks and requires extreme caution. Not all yellowing is reversible, especially if it stems from deep-seated impurities or permanent structural changes.
For significant or persistent yellowing, especially with valuable opals, consult a reputable jeweler or gemologist. Professionals can assess the opal type and cause of yellowing, offering expert advice on potential treatments or restoration. They can also perform professional polishing, which may rejuvenate a dull or surface-damaged opal.