Making real rubies at home!

The first thought you might have had when looking at this image is that these do not look like the rubies you know: They are not shiny and not transparent. But let me assure you: They are real!

What is a ruby?

Lets start at the beginning: What are rubies? Rubies are a variety of corundum, just like sapphires. Corundum is aluminium oxide (Al2O3), which is clear in its pure state. The interesting part is when metal contaminants come into play: Depending on the added element (or combination thereof), the crystal changes its color: Iron creates yellow to green, titanium and iron together create blue (typical sapphire) and chromium creates red/pink, which is what we are after.

The rubies I made contained about 99% Aluminium oxide (Al2O3) and 1% Chromium oxide (Cr2O3). Generally, more Al2O3 will create a lighter pink, and more Chromium will darken the color. I tried up to 5% Chromium, but at this point, the rubies got so dark that the red color was barely recognizable.

The materials

The base materials for the rubies I made were surprisingly available. However, the Aluminium oxide needs to be really pure. Sometimes, Al2O3 is sold as a sand blasting media (grey-ish), which turned out to be not pure enough, it just created black blobs. Next I got some at a mineral store from eBay, which claimed 99.99% purity, which probably was false since it didn’t work out as well. What ended up working were “microdermabrasion crystals”, a kind of cosmetic sand blasting media for skin. This pure white substance has the consistency of fine sand and is made up of pure Aluminium oxide. The second ingredient, Chromium(III) oxide powder, is sold as a green pigment because of its vibrant color. Since both of these substances seem to have “mainstream uses”, they are cheap and widely available, for example on Amazon or eBay.

The process of making the rubies

In order to make the rubies, you need to melt the powders (mixed). Since corundum melts at 2054°C, a normal melting furnace will not work. Some people use hydrogen torches, some use arc welders. I used the arc welder, since I have it at home. The basic setup is to ground a piece of graphite plate and use a graphite rod as the positive electrode. Graphite is used since it is the only widely available material that is conductive and able to withstand the intense heat. It really helps to drill a small blind hole into the graphite to prevent the powder from being blown away from the arc. I used a cheap milligram scale to create 10g batches of about 9.9g Al2O3 and 0.1g Cr2O3.

Simple schematic of the process.

Since this arc creates temperatures of over 3000°C, the material melts together and creates the ruby. Here’s a video I managed to make of the process:

Normally, the light of the arc would oversaturate my phone’s camera, but I put a spare welding shade in front of the camera, which worked surprisingly well.

This process is a bit messy, since the arc (which in itself is difficult to strike due to the missing shielding gas) spews parts of the powder everywhere. However, after the melting is done, you can check whether you made rubies by using blacklight (or other UV-lamp).

As you can see, rubies fluoresce vibrantly. All of the rubies I made fluoresce in that way, with the smaller ones being more bright than the bigger ones.

The internal structure

Now let’s get to the interesting part: The structure of the rubies. To view the structure, I cut a thin slice off a ruby using a diamond disc for my dremel. A diamond disc is definitely necessary, since corundum has a Mohs-hardness of 9, with 10 being diamond. This is also why it is used so frequently in abrasive tools. The cutting was a bit tricky, since the rubies are really brittle, but I managed to get slice with a thickness of about 0.8mm. This is how it looked under the microscope:

This is 40x magnification

100x magnification

400x magnification

You can clearly see the polycrystalline (poly = many) structure of the ruby. I’d guess that this structure also is the reason why the rubies are opague and not transparent, like most gem-quality rubies. I assume this structure is the result of the extremely fast heating and cooling of the ruby, leaving no time for the crystals to grow together.

Another quick fact: A very common way of professionally making synthetic rubies is the vernieult-process, also called flame fusion. You can read more about it here.

Thanks to ElementalMaker and NightHawkInLight for showing me this awesome process!

You can also watch my YouTube video on this process.

And as always: Thanks for reading!