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Cutting Small Opal Stone 2 – Sanding and Polishing

Aug 29, 2019 | From the Work Shop

In the previous video we talked about what we needed to do to prepare an opal gemstone for sanding and polishing.

In this video we discuss these two processes.

Sanding

We sand the opal gemstone on dry sandpaper.

There are two reasons for this.

The first being that by working the gemstone dry it is easier to see scratches, cracks and pits. When an opal is wet these features are less visual.

The second reason for using dry sandpaper is that sanding allows us to get a uniform ‘sweep’ on the surface of the gemstone thus making it easier to polish.

When using sandpaper, it is imperative that the gemstone is not overheated, which can occur when the gemstone is held for too long a period on the sandpaper. If too much heat is generated the opal will crack.

The most abrasive grit we use on an opal face is 320 grit however 600 grit is ideal as 600 grit scratches can be removed by the polisher with ease.

When the opal goes from sanding to polishing it is important to clean the gemstone, in soapy water, as grit (dirt) will contaminate the polishing pad and render it ineffective.

Polishing

As seen in the video we use tin oxide powder on a leather disc to do the final polish.

Tin oxide powder comes in a dry form and is mixed with water to make a paste.

Polishing involves working the gemstone face and sides on the leather disc using the tin oxide paste to get a ‘pull’ on the stone to achieve a polish.

The aim of polishing is to remove scratches.

When finished the surface of a polished gemstone should look like glass.

We recommend using a magnifying loop and good light to critique the final finish.

Doing the back of the gemstone is the last stage in finishing the opal gemstone.

We hope you find this information useful and informative.

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