1. Purple - Chromium Alum Crystals
- The growing solution will consist of a chromium alum solution mixed with an ordinary alum solution. Make a chromiun alum solution by mixing 60 g of potassium chromium sulfate in 100 ml water (or 600 g chromium alum per liter of water).
- In a separate container, prepare a saturated solution of ordinary alum by stirring alum into warm water until it will no longer dissolve.
- Mix the two solutions in any proportion that you like. The more deeply colored solutions will produce darker crystals, but it will also be harder to monitor crystal growth.
- Grow a seed crystal using this solution, then tie it to a string and suspend the crystal in the remaining mixture.
- Loosely cover the container with a coffee filter or paper towel. At room temperature (~25°C), the crystal can be grown via slow evaporation for as little time as a few days or as long as a few months.
- To grow a clear crystal over a colored core of this or any other colored alum, simply remove the crystal from the growing solution, allow it to dry, and then re-immerse it in a saturated solution of ordinary alum. Continue growth for as long as desired.
- A saturated solution of pure chrome alum will grow darker crystals, but the solution will be too dark to see through. Feel free to increase the concentration of chrome alum, but be aware that the solution becomes deeply colored.
- Notice that the chrome alum solution is a dark blue-green, but the crystals are purple!
What You Need:
- potassium chromium sulfate (chromium alum)
- clear glass jar
- coffee filter or paper towel
- pencil, knife, or stick (to suspend string)
- spoon or stirring rod
2. Blue - Copper Sulfate Crystals
Copper sulfate crystals are among the easiest and most beautiful crystals that you can grow. The brilliant blue crystals can be grown relatively quickly and can become quite large. Here's how you can grow copper sulfate crystals yourself.
Copper Sulfate Crystal Materials
- copper sulfate
Make a Saturated Copper Sulfate SolutionStir copper sulfate into very hot water until no more will dissolve. You can just pour the solution into a jar and wait a few days for crystals to grow, but if you grow a seed crystal, you can get much larger and better-shaped crystals.
Grow a Seed CrystalPour a little of the saturated copper sulfate solution into a saucer or shallow dish. Allow it to sit in an undisturbed location for several hours or overnight. Select the best crystal as your 'seed' for growing a large crystal. Scrape the crystal off of the container and tie it to a length of nylon fishing line.
Growing a Large Crystal
- Suspend the seed crystal in a clean jar that you have filled with the solution you made earlier. Don't allow any undissolved copper sulfate to spill into the jar. Don't let the seed crystal touch the sides or bottom of the jar.
- Place the jar in a location where it won't be disturbed. You can set a coffee filter or paper towel over the top of the container, but allow air circulation so that the liquid can evaporate.
- Check the growth of your crystal each day. If you see crystals starting to grow on the bottom, sides, or top of the container then remove the seed crystal and suspend it in a clean jar. Pour the solution into this jar. You don't want 'extra' crystals growing because they will compete with your crystal and will slow its growth.
- When you are pleased with your crystal, you can remove it from the solution and allow it to dry.
Tips & Safety
- Even a small increase in the temperature of the water will greatly affect the amount of copper sulfate (CuS04 . 5H20) that will dissolve.
- Copper sulfate is harmful if swallowed and can irritate skin and mucous membranes. In case of contact, rinse skin with water. If swallowed, give water and call a physician.
- Copper sulfate pentahydrate crystals contain water, so if you want to store your finished crystal, keep it in a sealed container. Otherwise water will evaporate from the crystals, leaving them dull and powdery. The gray or greenish powder is the anhydrous form of copper sulfate.
- Copper sulfate is used in copper plating, blood tests for anemia, in algicides and fungicides, in textile manufacturing, and as a dessicant.