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Wednesday, February 15, 2012

Using Oxalic Acid to Clean Idaho Star Garnet Rough

Somehow, the book has tripled in size and a new "first draft" is finally done! Now, it's time to take a little break, get the book cover designed and start cutting some gems. 

Star garnets, when found, almost always have a thick crusty layer of limonite on them. Before a gem-cutter can assess whether a crystal is worth cutting, this rind has to be removed. I showed a quick method that works great for single pieces in the last posting. If you have a larger parcel, acid might be the way to go.

Many mineral collectors use oxalic acid to clean quartz and other crystals. I'll be showcasing how well this method worked for my garnet. But first, I have to mention- this is dangerous stuff. Oxalic Acid is highly toxic and corrosive. If you're at all uncomfortable using chemicals and acids- DO NOT try this! Before using any chemical- always read the MSDS (Material Safety Data Sheet). They're easily found on google as are other mineral collector's write-ups about using this method. What's needed:

Distilled Water
Oxalic Acid (also known as “Wood Bleach”)
Iron-Oxide coated Garnet Crystals

Crock Pot
Good Quality Plastic Container (that fits inside the crock pot)
Measuring Cup
Gloves (Rubber or anything acid-proof)
Safety Glasses
Plastic Spatula or (preferably) Tongs

About 1.5 pounds of garnet crystals.

I also included some non-star garnet crystals (lower right) that were collected near
Emerald Creek. These will never cut asteriated gems and are sometimes found on ebay.

The container of oxalic acid says to use 12 oz. to 1 gallon of water. I mixed about half that amount: 6 oz. for half a gallon of distlled water.

Even though I bought my crock-pot for $2 I don't want to ruin it with acid. If there is a tiny crack or chip in the enamel, the acid will eat its way through. Instead, I'm heating pure water in the pot and then putting it in the plastic container with the acid-water mixture and the crystals.

Heat speeds up the reaction with the acid and cuts down on the time spent in acid. I had the crock pot setting on low and checked up on it periodically.

After a couple of days, a dark, greenish-brown tint developed in the inner container.

The acid ate away at the majority of the outer skin. Enough, so that I know how
and where to trim them. Some pieces may still benefit from a second soaking.

Top row consists of the non-star garnet crystals. Looks like they
 have a somewhat different type of acid resistant mineral coating.
After taking the crystals out of their container with plastic tongs, I rinsed them with lukewarm tap water and then soaked them in fresh water. Just to be safe, I added a little baking soda into the water in order to neutralize any residual acid. I've heard that the acid in the container can be reused. That's where heating it in the separate containers comes in handy. I can pop the lid on, clearly mark it, and put it far out of reach of any children and curious cats. Much better than leaving it in an unsecured crock pot. If you have no intention of re-using the acid- DO NOT POUR IT DOWN THE DRAIN OR ONTO YOUR YARD. First, neutralize the acid with baking soda or lime. Also, remember- NEVER ADD WATER TO ACID- it will splash you.

Feel free to leave comments about using this method. This is the first time I tried it and I welcome any additional tips. I've been restoring an old cabbing machine and am working on an article on “how to detect asterism” in rough garnet. Also, I've been doing lots of locality research and will be showcasing some interesting findings. Lots to look forward to in the coming months!

1 comment:

  1. Hello, Sir

    I have seen your web- and picturesque description of garnet and other rough and rough cutting
    I am from Jaipur (INDIA), and also as a family business in Jewelry business.
    I would very much like if you visit Ruby Rough section of my website-
    It may serve correctly to your needs if I am right, I can provide finest selected single gem rough pieces at lowest prices. I can even provide you with sapphire rough stone, Naphrite Jade, and some more interesting things you have never thought before; all 100% natural

    waiting for your response

    Rakesh Joshi