Beginning Lapidary, Part 2: Grinding & Polishing

Why cut your own cabochons? After all, plenty of beautiful stones are available for purchase already. But if you’ve ever had that idea for a piece of jewelry that you have yet to create simply because you haven’t found the right stone for it, then you’ve already felt the pull of lapidary. 

I know the equipment can seem intimidating. But once you know some basic terminology and tools, you’ll be surprised how quickly the rest will follow. Consider this primer your first step toward cutting gorgeous stones.

In Part One of this article, we looked at the four steps that a stone goes through from rough rock to polished cabochon, and the different saws and blades that you can use to cut them to your preferred size and shape. Now we'll focus on finishing and polishing these stones so they are ready to be created into jewelry. 

Purpose: A series of grinding wheels or flat laps, each one a finer grit than the last, used to shape and polish preforms into cabochons; can also be used to create flat stones, inlay work, and intarsia

Good to know: A water reservoir is attached to the machine, usually above the grinding surface. Water is slowly dripped, generally using only gravity and tubing, onto the grinding wheels, sanding belts, or flat laps to contin-ually cool and lubricate the stones you’re grinding or sanding.

To avoid contamination, always thoroughly clean your stone and the machine when moving to a different grit for grinding or sanding. Stray particles from a coarser grit can prevent you from achieving a satisfactory polish on your stone.

How to buy grinding wheels 

Grinding wheels are either metal wheels with abrasive particles, such as diamond, bonded to their grinding surface or wheels made entirely of abrasive material, such as silicon carbide. The metal wheels are generally more expensive yet last for a long time. The abrasive wheels are less expensive and wear slowly with use. You’ll need to dress abrasive wheels, using a dressing stick, from time to time to maintain a flat grinding surface. You can also shape these wheels to curves or angles to suit your needs. 

Decode those numbers 

When you shop for grinding wheels and sanding belts, they’ll likely be described with a series of numbers. You’ll need to understand these numbers in order to buy the properly sized grinding wheel or sanding belt for your machine.

For example, this grinding wheel has:

• 6x1-1⁄2", 80
  • a 6-in. (15.2 cm) diameter 
  • a 1 1⁄2-in. (38 mm) grinding-surface width  
  • and an 80-grit level of coarseness 

There are many polishing compounds available for lapidarists. Each kind of compound is best used when applied to a particular type of polishing wheel or lap. Select your polishing compound and delivery system based on the hardnesses and types of stones that you’re going to be polishing.

Always thoroughly clean your stone and the machine when changing to a different compound. Contaminated compounds or polishing pads will prevent you from achieving optimal shine on your stones.

Basic polishing compounds

• Cerium oxide: Good, inexpensive, multiuse polish suited for stones such as quartz, agate, and opal; perfect compound for beginners
  Best used with: Felt buff

• Aluminum oxide: Excellent, versatile, all-purpose polish suitable for most stones; excellent on hard stones 
  Best used with: Leather buff

• Tin oxide: Well suited for polishing softer stones and glass
  Best used with: Hard leather buff

• Diamond compounds: Expensive but precise polishing compound; no significant advantage for beginners, except when cutting hard stones, such as sapphire and ruby
  Best used with: Leather or specially made diamond disks or belts

 For more information, view our lapidary glossary page. 

Ready to invest in your own equipment? Check out this list of manufacturers and suppliers to start you on your way.