Tuesday, November 17, 2015

Making A Cabochon 101

Making a Cabochon 101



Cabochon is a cut of a gemstone that is flat on the back, domed on the top and can be round, square, rectangular, and free-form. The most common shape is an oval.  This cut of a gemstone is in contrast to a faceted gemstone such as a diamond.

When making a cabochon there are some common mistakes that if you learn to avoid, will make your finished stone much better.

If you want professional results, use professions tools, skills, polishes, and knowledge.  Taking a short cut will get you right where you don’t want to be. Remember, this is suppose to be a fun hobby—don’t stress out.  Ask us if you have questions about a particular rock or step in the process.

Assuming you are starting with a rock slab…

1st; Learn about the rock you are cutting.  If it has a special property such as asterism, iris effect, particular patterns, etc.  These need to have special care when cutting in order to get the correct effect. Find the part of the rock you want to cab.  Keep in mind the better the rough rock the better the finished cabochon.  We often see someone put half an hour into making a perfect cabochon out of a bland rock.  Make sure the rock is worthy of your time.

2nd; Check for porosity, hardness, cracks, and pits.  If a rock is porous or soft, it will not take a good polish without sealing it.  Use a stone sealer to fill any porous sections, cracks, and pits. There are a number of good products available.  We use EZ Bond® but Opticon® works well.

3rd;  Use a good machine designed for polishing a good rock.  Bench grinders are NOT a good machine and are NOT designed for polishing rocks.  Use the right tool for the right job!

4th; Go through the right sequence of grinding and polishing steps.  Some rocks require a coarser grit to start with.  Some a finer grit to start.  Diamond is superior to silicon carbide in terms of hardness, durability, and polishing.  But silicon carbide is less expensive and will work.  At the rock shop we go through the following steps;  80, 220,280,600,1200 grit diamond wheels.  Then we determine if it needs 3000 grit or if we can buff the stone with Zam®.  The longer you spend on the first step the less time you will have to spend on the last steps.

5th; When making a cabochon we do all the rough all the rough shaping with the 80 grit wheel.  Once you have a good shape and a dome that goes all the way across the stone you are ready to move to the next wheel.  After the first wheel, I like to do all the grinding/polishing in one direction on the stone and rotate it 90 degrees after each wheel.  That way I can see if I have left any scratches from the previous wheel.

6th; When you are done with the 1200 grit wheel, use cerium oxide or tin oxide on leather (cork or felt work well also) wheel for the final polish.  This will put that wet gloss on just about any rock.  If you have filled the cracks and pits with sealer, they will not get full of the polish leaving distracting lines in the cabochon.

7th; There is a lot more that can be learned about cabochon cutting. Ask if you have questions.  And remember to enjoy your finished product.

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