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Step 1.

Selection of Rough

Select a piece of rough gemstone material. For our project we have selected a piece of Bull Canyon Agate which came from the California/Nevada border. This 3 Oz.  piece of rough measures approximately 2” x 2 ½” x ¾” thick (fig. 1). We’ve selected this material because of the plumes & swirls imbedded in this type of Agate. Most Gemstone cutters will agree that Bull Canyon is considered one of the best Agates to work with.

 Figure 1

Step 2.

Cutting the rough Slab.

Pebbles for Slabs?

Cut several Slabs about 3/16” to ¼” thick from your piece of Rough selection. We have used a 6” Diamond Pacific slab saw and have made the cuts by hand (fig. 2). There is a large selection of Lapidary Saws on the market. To view some that are available, click here.

Figure 2

Step 3.

Slab preparation.

Using Gemstone Templates (figure 3), select the area of the Slab (figure 4) which gives you the desired visual appeal. Place the desired Template shape over the area and inspect for cracks. All cracks should be avoided, as the Stone may crack in two while working or once finished. Experience will teach you how and which cracks may be worked into a finished Cabochon.

Figure 3

Figure 4

Mark the desired Gemstone shape on the Slab using a sharp aluminum rod as a pencil (Figure 5). We have selected a 25mm x 13mm Oval Cabochon shape for this exercise.

Figure 5

Next, straight line the excess material to be sawn away to start the perform process (Figure 6).

Figure 6

Step 4.

Preform Preparation

Using our 4” Trim Saw, we followed the straight line saw marks and removed the excess material from the Gemstone perform (figure 7). Note: After cutting the perform, we have ample material to make another Cabochon from this Slab.

Figure 7

Step 5

Doping the perform.

There are numerous internet sites that sell Pre-forms. There are both  pros & cons about working with these pre-formed Stones. The one advantage we see is there is no dealing with the expense of a saw and the oily mess it creates. Another advantage is you don’t have the waste / unusable material to deal with. To view our selection of performs, click here.

If you are starting with performs, start your Gemstone Cabochon project here.

There are several ways to heat the Doping Wax. Electric Dop Pots, Alcohol lamps or an electric heat gun. All are acceptable depending on your preference.

In this exercise, we are using an electric Dop Pot. ( fig. 8)

Figure 8

Step 5A

Doped perform ready for rough grinding

Dop sticks can be of many types of material. We are using a ¼” wood dowel. (fig. 8a). Dop the Stone on the back side of your pattern mark. This will aid you in cutting the Stone to the precise shape and size.

Figure 8a

Step 6

Pre-forming

Pre-forming, Grinding and polishing Operations are accomplished using a Gem-maker or Cabochon grinding unit. There are several excellent Units on the market. To view some examples, click here.

Rough grinding is accomplished on a 100 grit grinding wheel. We use the metal  Diamond Wheels. These Wheels are more expensive than the Silicon Carbide Wheels, but in the long run, they are cheaper and require less maintenance.

 Rough grind the Cabochon to size and shape using 100 grit grinding wheel. (fig. 9).

Figure 9

Remove Stone from Dop Stick and mark the Girdle line at the base of the Stone with aluminum pencil. This dimension should be about 1/16” from the bottom ( fig. 9a). At this point, reinstall the Dop Stick on the shape marks side. All per-forming steps have been accomplished at this point.

Proceed to Rough Grind the top of the Cabochon (Step 7) with 100 grit grinding wheel.

Figure 9a

Step 7

Rough Grinding

Rough grind a 12 degree bevel around the Cabochon edge, starting at the girdle mark moving upward. This will leave an imperfect top. (fig. 10).

Figure 10

Now start doming the Cabochon with 100 grit, starting at the girdle mark upward, using a rocking motion, until the desired dome shape is attained. Make sure there are no flat spots on the top of the dome of the Cabochon (fig. 10a).

Figure 10a

Step 8

Fine Grinding

Start the Fine grinding process with 220 Grit sandpaper. Keep the Stone moving and remove all of the scratches made with the 100 Grit wheel, being careful not to reshape the stone or thin the Girdle edge by over sanding (fig. 11).

Figure 11

Step 9

Pre-polishing

Pre-polish the Dome and Girdle with 600 grit sandpaper, removing all of the scratches made by the 220 grit sandpaper (fig. 12). For a higher polish, re accomplish this step with 800 grit sandpaper.

Figure 12

Step 10

Final polishing

Final polish with a Tin Oxide paste on a cork or felt polishing pad. We are using a 24" Covington Combination Wet Belt Sander & Muslin Buff Polisher, model 465, with a Cork Belt & Tin Oxide (fig. 13).

Figure 13

Step 11

Finishing the Cabochon back.

Finishing the back of a Cabochon is not a requirement, but is highly recommended. It will enhance the beauty, look more professional (fig. 14) and  add value to the finished Stone if accomplished. This operation can be performed on a Flat Lap or a Face Plate-Polishing Head. Start with 220 Grit sandpaper to make the remove any saw marks and make the back flat, move to 600 Grit sandpaper to remove the 220 grit scratches and polish with a Tin Oxide paste on a polishing Pad.

Task completed and it's ready to be transformed into a piece of Designer Jewelry (fig. 14).

Figure 14

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