After putting in time and effort to grow a beautiful crystal, you may wish to preserve it. There is no one-size-fits-all way to preserve crystals. The technique to use depends on whether the crystal dissolves in water, whether it’s hygroscopic (absorbs water), and whether it oxidizes in air. Here is an explanation of ways to preserve homemade crystals. It’s advice from personal experience and from conservationists of mineral, fossil, and art collections.
Storing Crystals to Preserve Them
If you want to keep a crystal without applying any treatment to it, it’s important store it away from sources of damage.
- Humidity: Water and humidity are the enemy of most crystals grown in water and most metal crystals. The easiest way to protect crystals from water is to store them in a sealed container, along with a packet of silica gel beads. However, some crystals are hydrates and require water! Copper sulfate crystals are a prime example. If they dry out, they turn brown or gray and crumble. Crystals that need humidity should never be stored on cotton or paper, as they can wick away water, and never with silica or another desiccant. If you keep them sealed, place them on a non-wicking surface or at least use synthetic fabric and add a drop of water to the interior of the container.
- Temperature: Metal crystals are fairly tolerant of temperature changes, but most other crystals are not. Avoid extremely hot or cold temperatures or temperature swings. Especially avoid freezing crystals that contain water. Be aware some crystals spontaneous change form (allotrope) in response to temperature changes. Sulfur crystals are a good example. The shape change is cool, if that’s what you’re after, but most other types of homegrown crystals respond to the abuse by fracturing.
- Light: Lots of chemicals are photosensitive. Even if the chemical doesn’t decompose in response to light, the crystal may suffer damage. Decolorization is the most likely outcome. This affects gems, not just homemade crystals. Amethyst, aquamarine, topaz, and fluorite all lose their color after too much sun. Other crystals turn irreversibly dark. Store crystals in the dark. If you illuminate your mineral collection, remember fluorescent bulbs emit ultraviolet light. Glass between the bulb and the crystals filters some, but not all, ultraviolet light.
- Dust: Openly displayed crystals will require dusting. Usually, the safest course is using a soft, dry cloth. A (very) slightly damp cloth works for copper sulfate. Some people lightly oil their crystals. Oil fills in defects of many crystals, but it also attracts dust. Sealing your crystals protects them from dust.
- Chemical Exposure: Openly displayed crystals are subject to pollution and possibly other chemicals. Chemical reactions may occur. Usually, the problem is oxidation. Oxidation also occurs in air, which may be solved by storing crystals in oil or an inert atmosphere, like argon.
- Radiation: Light isn’t the only form of radiation that can damage crystals. Ionizing radiation breaks chemical bonds and causes problems. If you have a mineral collection, keep the radioactive ones away from the others.
- Bacteria: Bacteria don’t pose a threat to most crystals, but they will attack pyrites and other iron sulfide minerals. Storing the minerals in a dry environment minimizes the risk. Anecdotally, painting a solution of “Velpon” glue in acetone works to preserve pyrite.
Preserving Crystals With Plastic
Spraying or painting crystals with plastic (polyurethane, acrylic, etc.) is the easiest way to seal them. There are a number of sealants used to preserve paintings and crafts that work well. Some people use nail polish top coat, which is available both in normal and water-based form. Top coat is different from regular nail polish, which tends to yellow over time.
If you don’t mind encasing the crystal, embed it in a clear casting resin. Encapsulating doesn’t work well for all crystals. Some people report problems coating copper sulfate crystals, in particular.
Museums commonly use a polymer called Paraloid B-72 to coat crystals and fossils. Paraloid B-72 is an ethyl-methylacrylate copolymer. While expensive, it has the advantage of dissolving in a number of solvents, including ethyl acetate, ethanol, toluene, xylene, and acetone. It’s a good choice when you don’t want water near your crystal.
Rubber cement, vinyl acetate polymers, epoxy, shellac, and cellulose nitrate either discolor some crystals or else yellow over time. They may be fine for short-term preservation, but aren’t optimal.
Preserve Crystals With Oil or Wax
Preserve some crystals by spraying, painting, or dipping them with mineral oil (liquid paraffin) or wax. Some people use cooking spray or silicone oil. Oiling minerals is a common practice that protects crystals from humidity and often enhances their appearance. The downside is the oil may attract dirt or yellow over time. While oil preserves some crystals, avoid using it on salt. It’s a good idea to check the solubility of the chemical used to grow the crystal to make sure it won’t dissolve in your product. Alternatively, test oil on a small crystal sample before applying it to an important one.
Using Homemade Crystals in Jewelry
Homemade crystals are softer and more fragile than most gemstones. You can use them in jewelry, but need to take three factors into account:
- Hardness: Covalent crystals (e.g., sugar crystals) are inherently soft. Ionic crystals (e.g., borax, copper sulfate, salt) are harder, but can fracture or shatter if struck. Metal crystals (e.g., silver, bismuth, copper) are hard, but tend to have delicate edges.
- Solubility: Most homemade crystals grow from solution in water. So, if you’re going to use them in jewelry, the crystals must be water-proofed. Either spray or paint them with acrylic or encase them in resin.
- Toxicity: Take crystal toxicity into account. Many crystals are non-toxic or relatively safe, but others are poisonous. For example, bismuth crystals are stunning and often found in jewelry, but should never be worn by a child who might lick them. For adults, use care setting a potentially toxic crystal to minimize skin contact.
Ideally, set homemade crystals to wear as earrings or pendants. Crystals in rings and bracelet get knocked around more and may break. Protect the crystal (and your skin) by setting it in a metal bezel. You can even grow some crystals in-place in the bezel and then seal them after they dry or cool. Store jewelry made with crystals with care. Avoid hot or cold temperature or heating-cooling cycles and store jewelry away from direct sunlight.
Borax, Salt, Copper Sulfate, and More
Here’s a quick run-down for preserving popular types of homemade crystals.
Borax – Borax crystals are susceptible to humidity. If you live in an arid climate, you may be fine just keeping the dust off borax. In a humid area, store borax crystals in a sealed container with a desiccant, such as a silica gel packet. You can seal them with a polymer, if you like. Dip borax crystals in epoxy resin or spray them with polyurethane. Avoid nail polish because the discoloration that occurs over time shows up badly against the clear crystals.
Salt – Salt crystals are hygroscopic. As with borax crystals, they may be fine out in the open in a dry environment. But, if it gets humid where you live, store them sealed with a desiccant. Large crystals (such as halite lamps) may require dusting from time to time. Ideally, remove the dust with a dry cloth. You can remove the dust with a slightly damp cloth, but will dissolve a bit of the salt. You can remove dust with an oiled rag, but may get a sticky build-up from the oil over time.
Alum – Store alum away from humidity and dust. You can grow a clear alum layer over unstable or colored alum crystals to preserve the shape of the crystal and protect it.
Copper sulfate (copper sulphate) – These crystals are hydrates and require humidity. Either keep them in a high humidity environment or else seal them with a polymer, oil, or wax. Copper sulfate dissolves in water, so you can’t store the crystals under water.
Metals – Bismuth crystals get their rainbow color from the oxide layer formed in air. On the other hand, copper turns from reddish-metallic to green eventually after exposure to air or water. Silver develops black tarnish. Usually, metal crystals don’t require any special treatment, but some people spray them with sealant to prevent oxidation or corrosion.
Treat sugar crystals and most other “salt” crystals just as you would borax or table salt. Treat hydrates as you would copper sulfate.
Advice for Preserving Crystals
Expect some trial-and-error finding the best way to preserve a homemade crystal. You can save yourself some work by Googling preservation methods for specific crystals. Look for forum discussions involving people who routinely grow crystals or work as conservationists. Ideally, keep imperfect crystals to experiment with different preservation methods and take notes of your failures and successes. Feel free to share your experiences (both good and bad) in the comments section to help others preserve crystals.
- Fliedner, L. J. (1932). “The preparation and preservation of large crystals of chrome alum”. J. Chem. Educ. 9, 8, 1453. doi:10.1021/ed009p1453
- Koob, Stephen (1986). “The Use of Paraloid B-72 as an adhesive. Its application for archaeological ceramics and other materials”. Studies in Conservation. 31: 7–14. doi:10.1179/sic.1918.104.22.168
- McDougall, R. (2013) “Caring for Mineral Specimens“. McDougall Minerals.
- Parsons, A.L. (1922). “The Preservation of Mineral Specimens“. American Mineralogist 7:59-63.
- The Institute of Conservation. “Care and Conservation of Geological Specimens“.