Distilled Water in Gem Care
Distilled Water in Gem Care
The preferred aqueous medium for cleaning and storing hydrous and porous gemstones
Distilled water is water that has been purified by boiling and condensing its vapour, a process that removes dissolved minerals, chlorine, fluoride, and other chemical constituents present in municipal tap water or natural spring water. In gemmological practice, it is the recommended aqueous medium for cleaning and, in certain cases, storing gemstones that are sensitive to chemical interaction or mineral deposition — most notably opal, turquoise, and organic gem materials such as pearl and coral.
Why Tap Water Is Unsuitable for Sensitive Gems
Municipal tap water routinely contains chlorine or chloramine as disinfectants, fluoride as a dental additive, and varying concentrations of dissolved calcium, magnesium, and other minerals. On porous or hydrous gem materials, these constituents present several risks. Chlorine can bleach or alter the surface of organic materials and may attack the binder matrices in composite stones. Mineral-laden water, when it evaporates, leaves a residue of calcium carbonate or silica scale on faceted surfaces and within the pores of stones such as turquoise, lapis lazuli, and malachite. Over repeated cleaning cycles, this residue can dull polish, obscure colour, and — in porous materials — alter apparent hue by filling surface pores with white mineral deposits.
Applications in Cleaning
For the routine cleaning of sensitive gems, GIA recommends a solution of mild, unscented soap in distilled water applied with a soft brush, followed by a rinse in clean distilled water. This approach is appropriate for:
- Opal — a hydrous silica (SiO₂·nH₂O) that can absorb surface contaminants; distilled water avoids introducing mineral residue into its microstructure.
- Turquoise — a porous phosphate mineral highly susceptible to staining and chemical alteration; tap-water minerals and chlorine can permanently alter its colour.
- Pearl and coral — organic materials composed largely of calcium carbonate, which can react with acidic or chemically complex water; distilled water is chemically neutral and non-reactive under normal conditions.
- Emerald — heavily included stones with surface-reaching fractures that have been filled with oils or resins benefit from distilled-water rinsing, as tap-water minerals can deposit within fractures and alter the appearance of the filling.
Opal Storage in Distilled Water
A more specialised application is the long-term storage of precious opal in distilled water. Opal contains between approximately three and twenty-one per cent water by weight, held within its amorphous silica structure. In environments of very low relative humidity — such as heated interiors in winter climates, or pressurised aircraft cabins — opal can lose moisture, causing internal stress that manifests as crazing: a network of fine surface or internal cracks that permanently diminishes transparency and play-of-colour. Storing opal in a sealed container with distilled water, or simply placing a damp cloth of distilled water alongside the stone, maintains ambient humidity around the specimen and mitigates dehydration risk. Tap water is unsuitable for this purpose because prolonged immersion would allow mineral ions to migrate into the stone's pore structure.
It should be noted that not all opal authorities recommend full immersion as a routine practice; the consensus is that high-humidity storage is sufficient for most specimens, with immersion reserved for stones showing early signs of stress or those originating from localities known to produce particularly water-sensitive material.
Practical Considerations
Distilled water is widely available from pharmacies and supermarkets at modest cost, and small quantities are sufficient for gem-care purposes. Deionised water — produced by passing water through ion-exchange resins rather than by distillation — is functionally equivalent for most gem-care applications, as both processes remove dissolved ionic species. The two terms are sometimes used interchangeably in trade literature, though strictly speaking their production methods differ. For storage purposes, distilled water should be replaced periodically, as it can absorb carbon dioxide from the air over time, forming dilute carbonic acid; for short-term cleaning this is inconsequential, but for extended opal storage, fresh distilled water is preferable.