Purple Stone in Mortar

Making Paint Step 2: Grinding Stone

This post is part of series to show how I collect stones from the local landscape and make them into artist-quality watercolor paints. In the previous post, HERE, I showed how I find and collect the raw materials. In this post I’ll show how I turn the rocks that I collected into powder in preparation for filtering.


The Setup

When I sit down to powder the rocks into pigment, I use a very simple set of tools. I use a canvas painters cloth on the ground with a corrugated plastic sign on top of it. This catches the bits that fly off when I crack them.

Hard Rock Powders Soft Rock

The key here is to make sure that the rocks I collect are soft. Then the granite slab with the granite pounding rock will break them down pretty quickly and easily.


First Crack Reveals Interior Color

It’s always exciting to break a rock open for the first time. Often the inside is a very different color from the outside. In this case, it was just about what I expected – a rich burgundy iron oxide.


Keep Cracking!

I just keep using my big rock to break the pigment into smaller and smaller pieces until it looks like kitty litter.


Tiny Gravel in the Mortar

The small gravel goes into the high-powered tool, a granite mortar. This tool isn’t capable of breaking down big rocks, but the small ones are simple.


Granite Mortar Makes Powder

Then I use the mortar like normal, starting out slow and picking up speed as the gravel gets smaller and smaller. Eventually it looks like powder.


Water Helps Finish The Grind

At the very end I add water to the mixture. This lets the smallest particles stay suspended, up and out of the way of the pestle. I keep grinding and grinding the sand in the bottom until it feels like it’s not changing any more.

It is rare that a stone will grind all the way down to fine powder. Most stones contain sand and other hard minerals that just can’t be ground down. They will all get sorted out in the next step.

Stay tuned in to my blog to see the rest of the steps of the process!

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