How to Grow Blue Copper Sulfate Crystals

Copper Sulfate Crystals
Copper sulfate crystals are naturally blue and easy to grow.

Try this easy recipe for copper sulfate crystals. They are vivid blue crystals that are easy to grow. Grow a mass of crystals or a single large copper sulfate crystal.

Copper Sulfate Crystal Materials

Nothing could be easier! All you need is the chemical, hot water, and a container. Choose a clear container if you want to watch the crystals develop.

The exact amount of copper sulfate and water depends on the water temperature. Start with 200 grams of copper sulfate and 300 milliliters of hot water. Distilled water is best, but hot tap water typically works fine.

Copper sulfate crystals grow from a natural blue salt. (Stephenb, Creative Commons)
Copper sulfate crystals grow from a natural blue salt. (Stephenb, Creative Commons)

Make a Saturated Copper Sulfate Solution

First, you need a saturated copper sulfate solution so the crystals can form as the liquid evaporates. All you need to do to make the solution is to stir copper sulfate into very hot water until no more will dissolve.

Filter out the undissolved solid using a coffee filter or paper towel. Use the liquid for growing crystals.

Grow Copper Sulfate Crystals

There are two ways to grow the crystals. The easiest and quickest method is to simply pour the solution into a jar and wait for crystals to grow. Expect to see crystals within a few hours. It may take a couple of days for the crystals to reach their maximum size. Then, pour off the liquid and use a butter knife to scrape the crystals off the bottom of the container. Place them on a paper towel to dry.

If you want a larger crystal or a perfectly shaped one, there are two steps.

  1. First, pour a small amount of the saturated solution into a small plate. The large surface area on the plate helps the solution evaporate quickly, so you will get numerous small crystals quickly (within a couple of hours). Pick one or more of the best crystals and carefully scrape them off the plate. You can use a toothpick or a butter knife. These are seed crystals. They serve as “seeds” for larger crystals.
  2. Next, place these seed crystals into a jar or bowl of the remaining solution. Make sure they aren’t touching each other or else put them in separate containers. Check on the crystals about every half a day. If crystals start growing elsewhere on the container, you can remove the crystals to a clean container and pour the solution onto them. For really large crystals, you can prepare fresh solution to help feed the crystal growth. If you add new solution, be absolutely sure it is saturated before you add it or it may dissolve some of your growth! A good way to be sure the solution is saturated is to make sure no more copper sulfate will dissolve and then allow the solution to cool before adding it to your crystal.
  3. When you are satisfied with the crystals, remove them and allow then to dry. When the crystals are wet, they can be scraped from their container easily using a butter knife or gloved hand.

Tips & Safety

Copper Sulfate Structure
This is the crystal structure of copper sulfate. (Ben Mills)
  • You can dissolve more copper sulfate in hotter water.
  • Read the hazard label on the copper sulfate container. Don’t drink the solution and avoid touching it. Wearing gloves is a good idea. If you do get it on your hands, rinse them in clean water immediately.
  • Be aware copper sulfate stains skin and fabrics.
  • Copper sulfate crystals are actually copper sulfur pentahydrate. Thy contain water, so store crystals in a sealed container, like a plastic bag. If the water evaporates out of the crystals, the blue pentahydrate changes into a greenish-gray anhydrous form of copper sulfate. This is an example of efflorescence.
  • You can find copper sulfate sold as a root killer or algicide. Be sure to check the label to make sure it says the ingredient is copper sulfate. The product should look like blue sand or blue granules or a blue solution. If you buy copper sulfate solution, you may need to boil off excess water to get a saturated solution. Another option is leaving an open container of liquid until enough evaporates for the solution to become saturated.