Carnelian is a beautiful orange-red mineral that has been used in jewelry for thousands of years. Carnelian gets its reddish hue from trace amounts of iron oxide impurities. This striking stone has long been associated with vitality, energy, and passion. But can its color change over time?
The short answer is yes, carnelian can change color under certain circumstances. In nature, prolonged exposure to sunlight over a very long period of time can cause carnelian to fade somewhat. The iron oxide particles that give carnelian its color are photosensitive. When exposed to intense ultraviolet radiation from sunlight, the iron oxide can be altered or destroyed. However, this process takes many decades. So for all practical purposes, carnelian is a very color-stable gemstone.
Another factor that can affect carnelian's color is heat treatment. Heating carnelian to high temperatures can darken or enrich its orange-red color. Heat treatment is commonly used to improve the color of lower quality carnelian. The heat modifies the iron oxide impurities, bringing out a more vibrant hue. Most commercial carnelian on the market today has been heat treated to maximize its color.
Carnelian can also pale if subjected to acidic solvents or harsh chemical cleaners over time. The iron oxide particles that cause the red coloring can be dissolved out of the crystalline structure. So carnelian jewelry should not be exposed to acid, bleach, or other caustic agents. Gentle soap and water is best for cleaning carnelian.
An interesting historical fact is that in antiquity, crafters could bleach carnelian to remove its color completely. They would boil the stone in oil for seven days, causing the iron compounds to leach out. This produced a pale orange or yellow stone called ciranos. However, this laborious bleaching technique is no longer in use today.
In summary, carnelian is generally very stable in its orange-red color under normal wear and display conditions. Over an extremely long geological timeframe, extended sun exposure can cause fading. But otherwise, carnelian's rich color remains unfaded. Heat treatment and acids can alter the shade of carnelian, but are not factors for stones worn in jewelry. So you can be confident that a carnelian gem will retain its warm, fiery tones for a lifetime of enjoyment and beauty.
