Lapidary / Gemstone Community Forum

Creative Stone Works / Moderator, Michael Hoover => Intarsias / Commesso, and Composite Type Cabs / Tutorials => Topic started by: Taogem on January 09, 2009, 02:12:10 pm

Title: Tutorial on How To Make Assembled Gemstone Cabochons
Post by: Taogem on January 09, 2009, 02:12:10 pm
This was posted by Bob (bobby) of Bobs Premium Cabochons (

I am locking this particular post because discussion is ongoing within this thread (,1196.msg6020.html#msg6020), but I wanted to bring pin this part of that thread at the top here.

Thanks for taking the time to post this Bob.

Greatly appreciated! :)

I'll start with a photo of a triplet (three layer) assembled cab.
This is a piece of Woodward Ranch black plume. Often this material has fantastic plumes but it is so dense and black that the plumes don't show up unless you cut it real thin. If it is thin enough to show the plumes then it is too thin to stand alone as a cab. I started by slabbing is at about 1/16" thick. I then flattened  a slab of  translucent light grey agate. Next I flattened the Plume Agate and glued it to the translucent Agate. After the glue set I then ground it on the grinding wheel until it was maybe 1/32" thick. I then hand lapped it on a piece of flat glass using 220 grit tumbling grit and water. I kept going until I got the plumes that I wanted to show up. I then glued it to a flattened slab of clear Synthetic Quartz. This is what the "sandwich" looks like from the side. The translucent Agate is on the left, the Plume in the middle and the clear Quartz on the right.
Here is a look at the "sandwich" through the translucent Agate.
Here is a look from the clear Quartz side.
At this point I cabbed the "sandwich" , polishing both the front and back.
And now the detail:
1. Use a fairly new piece of flat glass. After you have ground a few slabs on it the center will become dished. I use a piece about 6" square. Put a pinch of 220 grit abrasive on the glass, wet it slightly and start moving your slab around in figure 8 circles. Keep grinding while adding additional pinches of grit and water as the grit wears down. Stop once in a while, rinse the slab off and dry it. If you have an even frosty appearance with no evidence of saw or grinding marks you are ready to go to the next grit. On a 2" diameter slab this coarse grind should take about 15 minutes.
2. Rinse the glass thoroughly. Go to the 400 grit step and repeat the grinding activity of moving in a figure 8 pattern until the 220 grit pits are looking much smaller.
3. Repeat the above step with 600 grit.
4. Clean everything up (it gets a bit messy). Set this slab aside and repeat the above steps with the slab that you are going to glue the first one to.
5. Wash the slabs in hot soapy water, rinse them in hot clean water and Don't touch the surfaces to be glued with your fingers. Using a clean paper towel, wipe both pieces with Denatured Alcohol.
6. Place both pieces on a small paper plate under your "gooseneck" lamp with a 100 watt bulb. Let them heat for about 10 minutes. On a small piece of WHITE paper, mix the two parts of the Epoxy 330 by swirling it together with a tooth pick. Don't "whip" it together because it will introduce bubbles. From here on bubbles are your enemy! Mix it until you can't see any swirl patterns in the Epoxy. Mix for one minute more. Slide the piece of paper under the lamp and heat it for about 3 or 4 minutes until the Epoxy mixture becomes rather liquid. The bubbles should have dissipated by this time.
6. This is an important step! Pick up one of the slabs by the edges and scoop some of the adhesive onto  it. Spread the Epoxy slowly and carefully trying not to introduce bubbles. Lay it aside and do the same to the other slab. Make sure you are spreading the Epoxy on the prepared sides of the slabs!
7. The most important step! Lay the two slabs together by touching the edges in a "V" and move them together as you squish the Epoxy to the side away from the "V". This way you are not trapping a big bubble between the slabs. Grip the two slabs betwen the fingers on one hand and slowly apply pressure as you move the pieces a slight amount against each other. Your objective is to squeeze the excess Epoxy and any possibly entrapped bubbles out from between the slabs. When you feel the slabs dragging slightly against each other stop moving them and hold the newly asembled "sandwich" at a steep angle to the bulb in the lamp and look for any entrapped bubbles. If you see any go back to squeezing and moving the sabs to get the bubble worked out to the side.
8. Place the "sandwich" back under the lamp and continue heating for about 30 minutes. Turn the lamp off and go to bed. You've worked hard so far and you need a good nights rest!
9. Wake up refreshed and grind or sand the prepared color (plume or whatever) layer down to the desired pattern. Go through the three grits and set this "sandwich" aside. Prepare the final slab surface by going through the above three grinding steps.
10. Glue the two slabs together as above. When the Epoxy is set up hard cab as usual.
A warning! Don't use 5 minute Epoxy! You don't have enough working time before it starts to set up!
Some more pictures:
A very thin slice of Dendritic Agate with a clear backing.
A side view.
An Australian Opal Triplet (clear Quartz top, a thin layer of Opal and a Basanite back).
A Spencer Opal Triplet.
Another Spencer Opal triplet.
Have fun making assembled cabs!