How to Preserve Borax Crystals

Borax crystals are among the easiest crystals to grow, but knowing how to preserve them is helpful because they whiten and degrade over time. Here is a look at why the crystals change, how to preserve them, and tips for avoiding common problems.

• Borax crystals turn white over time.
• The best preservative is Paraloid B-75, but you can use an acrylic or polyurethane craft spray.
• Another option is storing them in alcohol.

Why You Need to Preserve Borax Crystals

Borax crystals benefit from preservation because they spontaneously change structure according to environmental conditions. They aren’t the only crystals that do this. Copper sulfate crystals turn from crystalline blue to gray crumbles after exposure to air. Sulfur crystals spontaneously change shape according to temperature. Borax crystals change according to temperature or humidity, so the chances are low of keeping them pretty and pristine without protection. Usually, they turn white and powdery.

What Exactly Are Borax Crystals?

Borax crystals grow from a saturated solution of borax in water. But, borax is a common name for a collection of chemical structures.

The dry powder you dissolve is a hydrated boron salt (a borate) of sodium. While it’s called sodium tetraborate decahydrate, which has the formula Na₂B₄O₇·10H₂O, its crystal structure indicates the real formula is Na₂B₄O₅(OH)₄·8H₂O. The rhombohedral crystals you grow from a solution in water are borax pentahydrate (Na₂B₄O₇·5H₂O, more accurately Na₂B₄O₅(OH)₄·3H₂O). If you heat either the tetrahydrate (the starting material) or the pentahydrate (the crystals) to around 116-120 °C, the structure changes into borax dihydrate (Na₂B₄O₇·2H₂O or Na₂B₄O₅(OH)₄). Further heating eventually drives off the water, yielding anhydrous borax, Na₂B₄O₇, which has four possible crystal forms.

So, heat and hydration levels are the main factors that cause borax crystals to change over time. With that in mind, here are steps to take to preserve the crystals.

How to Preserve Borax Crystals

You have several options for preserving the crystals:

1. Seal them with a polymer. The polymer preferred by archivists for mineral specimens is called Paraloid B-72, which is an ethylmethylacrylate polymer. Less expensive options include acrylic or polyurethane sprays from a craft store for sealing paintings or papers. Be aware acrylic often contains water, so don’t go overboard applying it. Casting the crystals in resin may or may not work, depending on the formula. Also, some resins discolor after a matter of months or years.
2. Seal them with wax or oil. There are two disadvantages. First, the coating can dull the sparkle. Second, the organic molecule attracts dust. But, it’s an easy and inexpensive option.
3. Store the crystals in alcohol. Borax is not soluble in alcohol. Just be sure you use absolute alcohol (or close, like 99% rubbing alcohol or denatured alcohol) and not alcohol that contains a lot of water.

What to Do If You Don’t Want to Use Chemicals

If you choose not to preserve the crystals using a chemical, take steps so they last as long as possible. Wrap them in tissue paper or paper towels and store them in a cool, dark place. If the crystals start turning white, mist them with water. This dissolves some of the crystal, but exposes the clear portion beneath the powdery residue.

Tips for Avoiding Problems

If you want the crystals to maintain their beauty, avoid these common problems:

• Don’t expose the crystals to temperature extremes and minimize temperature changes. Temperature can change crystal structure and either cause the chemical to absorb or release water.
• Don’t use a coating that discolors over time. So, avoid using nail polish, top coat, or some types of epoxy. Ideally, test a sealant over time and see if it yellows.
• Avoid sunlight. Sunlight not only affects temperature, but the ultraviolet radiation is the driving force behind discoloration in some polymers.
• Avoid swings in humidity. Sealing the crystals should protect you against this. But, if you keep unsealed crystals, don’t expose them to either extremely dry or extremely moist air.

References

• Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119.
• 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.1986.31.1.7
• Levy, H. A.; Lisensky, G. C. (1978). “Crystal structures of sodium sulfate decahydrate (Glauber’s salt) and sodium tetraborate decahydrate (borax). Redetermination by neutron diffraction”. Acta Crystallographica Section B. 34 (12): 3502–3510. doi:10.1107/S0567740878011504