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Tuesday, November 8, 2011

How to Clean Star Garnet Rough

Larger star garnet crystals have a tendency to be encrusted in a thick layer of rusty iron oxide. It can be tough to remove and there is no way to tell if a crystal is even worth cutting unless this layer is removed.

This large crystal fragment barely has any garnet peeking out. I chose
 this piece because I thought I saw some silk on the surface.  A penny is 
provided for scale. The preying mantis volunteered his modeling services.

The use of oxalic acid is a well known method for removing iron oxide staining from quartz and I've heard it recommended for star garnet crystals too. Commonly known as "wood bleach", most hardware stores carry it in stock. The downside to oxalic acid is that it is corrosive and toxic. I've been avoiding cleaning my crystals with this method since I share my workshop with a very inquisitive Siamese Cat. Just like a small child- I know he'll find a way into this potential toxic garnet stew.

Recently, I heard of a much easier suggestion- a brass bristle brush. Steel might work too. I had neither. However, I am restoring a rusted-out cabbing machine and do have a rust/paint stripping abrasive wheel (manufactured by 3M) that fits into a hand power drill. Here are the results:

 The same crystal face. Rust is nearly all gone. It worked!

A very silky portion of the crystal. This one is a cutter.

This is a great method for a peek into your garnet rough- especially if you don't have a cabbing machine setup. I did test for asterism with the "oil test" and discoverd that this crystal will yield some brightly starred gems. Has anyone tried the brass or steel brush method?


  1. Great job on this page! I did not even know the asterism could be tested on an entirely rough stone. If you get the time that would be a great add-on to this page! Thank you.

  2. I tried it with a steel brush for my dremel, and it did sorta worked but seemed to wear out the brush super fast. More so then the garnets crust.

  3. Ive tried many brushes and here is what ive found; Dont buy the expensive brushes as the 10 dollar one lasts only a little longer than the 3 for five bucks. I use a decent drywall cutting bit to do the bigger stuff and then finish with the wheel. Brass and steel brushes work well but i find the steel brush leaves a metallic stain on the stone that requires further cleaning after. Many wheels later i highly recomend a face shield because they dont last long and tend to fly apart. I have used a large side grinder with a stainless wheel on big matrix chunks with some success. As long as the rpms are low it does a decent job cutting threw the mica schist. while a high rpm does a great job of power stripping the stones out.

    good luck out there

  4. Do you think it would work to try removing some of the outside material with the grinding wheel or some of the other wheels?

    1. Hi Maryann,

      Yes, any grinding wheel will work. Back when I wrote the article, I didn't have a cabbing machine yet. I still like this method because it doesn't grind away any crystal faces and that can be a help when you're trying to orient a crystal to cut a star.