How to Grow Blood Red Potassium Ferricyanide Crystals

You can grow beautiful red crystals from potassium ferricyanide, a blood red salt.

It is commonly used as an ingredient in cyanotyping – and despite its name, quite safe to handle.

Since it’s hard to find household materials that can form red crystals, I was very excited when I got my hands on some potassium ferricyanide.

A closeup of potassium ferricyanide powder. I love that color!

After a year or so, I’ve now grown quite a few crystals with it. In this guide, I’ll share the method I used, several interesting things I discovered, and of course, lots of pretty pics.

Materials

To grow these crystals, you’ll need:

• Potassium ferricyanide powder
• Very hot water
• A glass jar
• A flat dish
• A plastic spoon
• A beaker (or a Pyrex dish)
• Thin nylon fishing line (optional)
• An electronic balance

Make sure all your containers and spoons are non-metal, as the solution reacts with iron ions to form Prussian blue. That’s how cyanotyping works, but we don’t want that to happen.

Safety

It’s safe to handle potassium ferricyanide. As a mild irritant, if you touch it, do wash your hands afterwards.

Also, never add acid to the compound or heat it over 150°C. This will cause it to release highly toxic cyanide gas. Not cool.

Procedure

Now, let’s start growing these crystals!

First, dissolve 50g potassium ferricyanide per 100mL of hot water in a beaker (or any heat resistant, non-metal container), to create a saturated solution.

Now, stir the solution until all the powder dissolves.

Once everything has dissolved, the solution should appear dark brown, almost black.

Let it cool to room temperature.

Optionally, filter the solution into a new container. You can use a coffee filter – even tissue paper will work.

Filtering helps to get rid of dust and impurities in the solution that can mess with the crystal growth.

After that, pour about 30mL of solution into a small, flat dish.

Leave it overnight.

The next day, small red crystals should have formed in the dish. These are pure potassium ferricyanide crystals.

For me, only one crystal formed at first.

Then on the second day, a bunch of others started popping up.

Some of you might run into one of two problems at this step. Both are easy fixes:

• No crystals are forming inside the dish

Your solution is not saturated enough. Try reheating the solution and dissolving more power inside. Then repeat the procedure.

• Red dust is forming on the surface of the solution and inside the dish

The dust actually contains thousands of tiny crystals. Why?

Because the solution is too saturated (you dissolved too much powder). This might be more common if you live in a colder place, as cold water can dissolve less powder compared to hot water.

To fix this, try reheating the solution, and diluting it with about 10% more water vs the total volume of the solution. This should dissolve all the dust.

Regardless, once crystals do form, you can proceed with the next step:

Choose a decently sized one, and tie it to a nylon fishing line attached to a pencil/stick.

Hang the crystal in the solution you prepared earlier.

Place the setup somewhere undisturbed and dark (prolonged exposure to light will cause it to decompose, more later).

Now, all we need to do is to wait.

After 1 week, here’s what my crystal looks like:

I placed a light behind the solution – otherwise it is too dark to see the crystal.

You can keep growing it as long as you have enough solution. But after 2 weeks my crystal was already touching the surface of the solution, so I had to take it out.

Beautiful!

But we’re not done yet.

At this point, the leftover solution should have become darker than before. This is because potassium ferricyanide solutions decompose under sunlight, or when left standing in air.

Left: Fresh solution, Right: Dark solution (left for 1 month)

For some reason, crystals that grow from darker solutions are longer and more needle-like.

If you try hanging another small crystal into this dark solution and let it grow for one week, the crystal will look like this:

It’s very hard to grow single crystals from darker (and hence spikier) solutions.

Left: Crystal grown from fresh solution, Right: Crystal grown from dark solution

Instead, you can take advantage of this spikiness to grow crystal clusters instead.

Here’s how to do it:

Pour the dark, leftover solution into another container. I used a glass dish.

In this case, there is no need to hang a seed crystal inside the solution. Just let the crystals form naturally at the bottom of the container.

After a week, pour away the solution, and you should see clumps of long, red crystals.

You can stop here if you’re satisfied.

If you want to grow them even bigger, select a nice cluster:

Then, place it at the bottom of a new dish filled with more potassium ferricyanide solution.

The reason we isolate this specific cluster is that this will allow it to grow much faster.

Wait another week, pour away the solution once again.

You should see something like this:

We see exotic crystals online, and in shops, but it’s incredible how you can just grow these at home.

That’s all for this guide.

If you plan on doing it yourself, then have fun! Feel free to leave your questions in the comments below.

And if you manage to grow some nice crystals, do share them with me! I’d love to feature them on this website. I’m planning to create a new page showcasing crystals that others have grown.

To see more cool crystals, consider visiting my dad’s YouTube channel, or check out this article on how to grow alum crystals.

As always, happy growing!