Pearls are not inherently hard, despite their use in jewelry alongside harder materials. Their composition and formation result in a relative softness that requires specific care to maintain their integrity and appearance.
The Science of Pearl Hardness
Hardness, in gemology, refers to a material’s resistance to scratching, quantified by the Mohs scale from 1 (softest) to 10 (hardest). Pearls typically rank between 2.5 and 4.5. For comparison, a human fingernail is about 2.5, and a copper penny is around 3.5, meaning pearls can be easily scratched by many common objects, including other jewelry.
Pearls are formed inside mollusks as layers of nacre, a composite material primarily made of calcium carbonate (aragonite) and an organic protein called conchiolin. Microscopic aragonite platelets are arranged in a “brick-and-mortar” fashion, held together by elastic conchiolin layers. This layered construction, while contributing to their luster, does not provide high scratch resistance.
Factors Influencing Pearl Durability
Beyond hardness, a pearl’s durability includes its resistance to breaking, chipping (tenacity), and chemical or environmental damage (stability). Conchiolin, the organic binder, significantly contributes to the pearl’s tenacity, allowing it to absorb impacts and resist shattering more effectively than pure aragonite. This layered structure helps distribute stress and can isolate minor cracks, preventing them from spreading.
Despite this internal resilience, pearls are susceptible to external factors. Their calcium carbonate composition makes them vulnerable to acids, even mild ones like perspiration or vinegar, which can dull, effervesce, or dissolve the surface. Chemicals in perfumes, hairspray, cosmetics, and household cleaners can also damage the nacre. Extreme temperature changes and dehydration can lead to cracking or discoloration, while abrasion from rough surfaces or harder jewelry can easily scratch the nacre.
Caring for Your Pearls
Proper care is important for maintaining the beauty and longevity of pearls. A common guideline is “last on, first off”: pearls should be the last item put on after applying cosmetics, perfumes, or hairsprays, and the first item removed. This practice minimizes exposure to chemicals that can degrade the surface.
After each wear, gently wipe pearls with a soft, damp cloth to remove oils, perspiration, or dirt. Avoid harsh cleaning agents, ultrasonic cleaners, or steam cleaners, as these can severely damage the nacre. For storage, keep pearls separate from other jewelry in a soft pouch or fabric-lined box to prevent scratches. Storing them in a slightly humid environment, rather than an airtight container or very dry safe, helps prevent dehydration and cracking.