The Natron Theory

Granite, which has a hardness of 7 on the Mohs scale, is so hard that no acid or alkali can harm it. Our ancestors had to use copper chisels and stone tools to carve granite.

WRONG!
Many different chemicals can damage granite, and among them there is also an acid.

Hydrofluoric acid?

Yeah, for the sake of completeness, there is an acid that etches granite. But...

Hydrofluoric acid is nearly impossible to store because it corrodes everything, including glass, ceramics, and metals. Moreover, it is highly toxic. We don't believe our ancestors were handling this acid. They have used something else.

Natron!

However, there is another substance mentioned before, sodium carbonate, or natron in short (Na2CO3), a white powder, which, when heated to 851 degrees Celsius, eats granite for breakfast.

And here, we could recap the list we've already seen of the various uses the Egyptians had for natron. They knew this material very well, not like in our modern times.

How is etching granite possible?

The essence of the matter is that granite is a complex material, with 70-77% of it being SiO2, or commonly known as quartz. The rest are tiny-tiny, colorful granite (feldspar) grains. Molten sodium carbonate (natron) breaks down quartz, and so, granite as well, liberating the tiny-tiny, colorful grains.

This is a piece of red granite after a good bath in molten natron.

What is molten natron?

Molten natron is a liquid. At 851 degrees Celsius, it turns into a glowing, corrosive reddish liquid from its fine white powder form.

Reaching a temperature of 851 degrees Celsius is quite easy with the help of charcoal.

(The natron doesn't etch the stone in this video, but only because the heat dissipates immediately. Don't be impatient.)

A grill chimney!

As you've seen, all you need is a grill chimney and some charcoal to be able to etch granite at home.

Additionally, you'll need some kind of container to put your stone and natron in. This could be an empty tin can.

This setup retains the necessary heat for the natron to stay molten and do its work. And no, this is not how ancient Egyptians did this.

Volcanic rock types

Molten natron also etches all other volcanic rocks with quartz as their binding material.

Without claiming to be exhaustive, it also etches these rocks: sandstone, volcanic tuff, diorite, quartzite, basalt.

Which means if you can work on granite with molten natron, you can also work on these stone types as well.

It's a total misconception to believe that granite is some kind of invulnerable, sacred substance. It's just like any other material in our surroundings. It has its own 'enemies.'

It's time to topple the second domino.