Growing crystals on bones is a striking science project that coats real animal bones in sparkling mineral formations. The process uses a supersaturated solution, most commonly borax dissolved in boiling water at a ratio of 3 tablespoons per cup. You submerge a cleaned bone in the solution, let it cool undisturbed, and crystals form directly on the bone’s textured surface over 12 to 24 hours.
Why Bones Make Great Crystal Surfaces
Crystals need something to cling to as they form, and bones are ideal. Their surface is full of tiny ridges, pores, and rough textures that give crystal “seeds” plenty of anchor points. This is the same principle behind real bone biology: in living tissue, hydroxyapatite crystals grow within the gaps between collagen fibers, using those organic structures as a scaffold. Your project mimics this in a simplified way, replacing the body’s slow mineral deposition with a fast-acting supersaturated solution.
Chicken bones, turkey bones, and small beef bones all work well. Skulls and jawbones from craft suppliers or nature finds are popular choices for display pieces. The more textured and porous the bone, the better the crystal coverage.
Choosing Your Crystal Chemical
Three common household chemicals produce distinct crystal types, and each gives a different look on bone.
- Borax produces chunky, angular crystals that look like frost or snowflakes. They’re durable enough to last for years on display. You can also make translucent black crystals by adding food coloring. Borax is the most popular choice for bone projects because the crystals are sturdy and forgiving to grow.
- Alum (potassium alum) forms large, clear crystals that resemble raw diamonds. These have a more gem-like quality and work well if you want a cleaner, more refined look on a small bone.
- Monoammonium phosphate creates crystals that look like emeralds. By adjusting growing conditions and adding dye, you can imitate amethyst, citrine, or aquamarine. This option gives the most dramatic color results.
For a first attempt, borax is the easiest to find (it’s sold as a laundry booster) and the most reliable.
Preparing the Bone
Start with a bone that’s been thoroughly cleaned of all meat, fat, and connective tissue. Simmer the bone in plain water for 30 to 60 minutes, then scrub it with an old toothbrush. Any remaining grease will repel the crystal solution and create bare patches. If you want an extra-clean surface, soak the bone in hydrogen peroxide (the 3% drugstore kind) overnight after simmering.
Let the bone dry completely before placing it in your crystal solution. A dry, degreased bone gives crystals the best grip.
Making the Supersaturated Solution
The key to crystal growth is supersaturation: dissolving more chemical into hot water than the water can hold at room temperature. As the water cools, the excess material has nowhere to go except out of solution, and it deposits as crystals on any available surface.
For borax, dissolve 3 tablespoons of powder into each cup of boiling water. Stir continuously until the powder disappears. If a few grains remain at the bottom after a full minute of stirring, that’s fine. It means you’ve hit true saturation. Pour the solution through a coffee filter into your growing container to remove any undissolved particles. Stray particles floating in the solution will compete with the bone for crystal growth, pulling material away from where you want it.
If you want colored crystals, add food coloring to the solution after filtering. A few drops produce a tint; a full tablespoon creates deep, saturated color.
Submerging and Growing
Place the bone in a heat-safe glass jar or container, then pour the hot filtered solution over it until the bone is fully submerged. If the bone floats, weigh it down with a clean glass marble or a piece of fishing line tied to a butter knife laid across the jar’s rim.
Set the container somewhere it won’t be bumped or jostled. Vibrations disrupt crystal formation and produce smaller, less defined shapes. A countertop away from foot traffic works well. Cover the top loosely with a paper towel to keep dust out while still allowing heat to escape.
Crystals will begin forming within a few hours, and most growth happens in the first 12 to 24 hours as the solution cools to room temperature. You’ll see small formations first on the roughest parts of the bone, then gradually spreading across smoother areas.
Controlling Crystal Size
The single biggest factor in crystal size is how fast the solution cools. Slow cooling produces larger, more dramatic crystals. Fast cooling produces a coating of tiny crystals that looks more like frost or sugar.
To grow large crystals, slow the cooling process. Wrap the container in a towel or place it inside an insulated cooler. This can stretch cooling time from a few hours to overnight, giving crystals more time to build layer by layer. For the largest possible crystals, you can leave the bone in the solution for two to three days.
To grow a dense, even coating of small crystals (which can look beautiful on skulls), let the solution cool quickly at room temperature or even place the container near a window in winter. The rapid temperature drop forces crystals to nucleate in many spots at once, creating a uniform sparkly layer rather than a few large formations.
Removing and Preserving Your Crystal Bone
Once you’re happy with the crystal coverage, carefully lift the bone out using tongs or a slotted spoon. Set it on a drying rack or paper towel with the most crystal-covered side facing up. Let it air dry for several hours.
Borax crystals are water-soluble, so the finished piece needs to stay dry. Display it in a spot away from humidity. A light coat of clear acrylic spray sealant adds a layer of protection against moisture and makes the crystals slightly more durable for handling, though it can dull the sparkle slightly.
If your first attempt doesn’t produce enough coverage, you can reheat the solution back to boiling, re-dissolve any crystals that formed on the container walls, and submerge the bone again for a second round. Each cycle adds another layer of crystal growth.
Safety Basics
Borax has low acute toxicity, but it’s classified as a potential reproductive hazard at high exposure levels, so keep it away from pregnant individuals and small children who might ingest it. Work in a ventilated area when stirring the hot solution, since the steam can carry fine particles. If you spill the powder, avoid creating clouds of dust. Wash your hands after handling any crystal chemicals, and don’t use your crystal-growing containers for food afterward.
Alum is the safest option of the three for younger kids, since it’s food-grade and commonly used in pickling. Monoammonium phosphate is also relatively low risk but should still be kept away from mouths and eyes.