Grow Natural Bright Red Potassium Ferricyanide Crystals

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Potassium ferricyanide is also called "red prussiate". (Paul's Lab, Flickr)
Potassium ferricyanide is also called “red prussiate”. (Paul’s Lab, Flickr)

Grow natural red monoclinic crystals without using any dye. The chemical used for the crystals is potassium ferricyanide (K3Fe(CN)6) or ‘Red Prussiate of Potash’. It has the C-N group, which is the cyanide, but it’s bound in the crystal and won’t hurt you.

Materials

93 g potassium ferricyanide
200 ml warm water

Procedure

  1. Dissolve 93 grams of potassium ferricyanide and 200 ml warm water into a clear container. If you can’t measure the powder or water, stir in enough potassium ferricyanide that it stops dissolving in the warm water, making a saturated solution.
  2. Now, you can simply wait for crystals to grow or you can try to grow a single monoclinic red crystal. To do this, you need a seed crystal.
  3. To get a seed crystal, pour a few drops of your solution onto a plate or saucer. Allow this liquid to evaporate to form seed crystals. Select the best crystal and place it in a clean container with the rest of the solution.
  4. Cover the container with a paper towel or coffee filter to keep it clean, but permit evaporation.
  5. Leave your solution undisturbed, but check on it daily to observe crystal growth.
  6. Once the crystals have reached the desired size (a week or two), remove the crystal and allow it to dry on a paper towel.
  7. Store your crystal wrapped in a piece of tissue.

Tips for Success

The IUPAC name for potassium ferricyanide is potassium hexacyanoferrate(III). (Maxim Bilovitskiy)
The IUPAC name for potassium ferricyanide is potassium hexacyanoferrate(III). (Maxim Bilovitskiy)

If you are having trouble getting all of the solid to dissolve, try using hotter water. If the solid still won’t dissolve, let the solution to settle out, then use only the clear portion for growing crystals. This solution may not be saturated initially, but as the water evaporates, it will become more concentrated.

You can control where the crystals grow. If you have solids in your starting solution, the crystals will form (nucleate) around these particles. This is why a seed crystal helps with growing a large single crystal. It’s also why a solution with undissolved particles develops into a mass of small crystals.

You can buy potassium ferricyanide at Amazon and other places as a photography chemical.

While you’re waiting for the crystals to grow, there is another project you can try with your leftover potassium ferricyanide: burning it together with potassium chlorate. Now, it turns out, the rate at which the mixture burns can be predicted based on its color. It’s a pretty awesome pyro project.