Lapidary / Gemstone Community Forum

How it began. I initially used a long  oval template and roughed out the cab from this piece.
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The preform back had lots of vugs, pits and such that I had to remove to make the cab but in removing them the cab preform ended up rather thin to cab and still expect it to be durable as a large cab. I decided to back it with a slab of Basenite which would make it durable as well as enhancing the contrast of the plumes. Here it is with the Basenite glued to the back. I used a plate of glass and tumbling grit to grind both pieces perfectly flat and then mixed up and applied Epoxy 330 to glue them together. I let it set overnight to allow the adhesive to cure.
(https://gemstone.smfforfree4.com/proxy.php?request=http%3A%2F%2Fi151.photobucket.com%2Falbums%2Fs160%2FRocksbob%2FNew%2520Photos%2Fb901bdaf-a557-46f2-96f2-ff6a995870bc_zpsb2264b81.jpg&hash=787390add577e9316843ccf87d1c13e4) (http://s151.photobucket.com/user/Rocksbob/media/New%20Photos/b901bdaf-a557-46f2-96f2-ff6a995870bc_zpsb2264b81.jpg.html)
Side view.
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I ground the Basenite backing down to the pre-shaped preform's girdle.
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(https://gemstone.smfforfree4.com/proxy.php?request=http%3A%2F%2Fi151.photobucket.com%2Falbums%2Fs160%2FRocksbob%2FNew%2520Photos%2F37651265-7e6e-4e9f-978a-b43704794de9_zpsde657896.jpg&hash=74b4c6d36c4b7cb551a140ce20f8e60b) (http://s151.photobucket.com/user/Rocksbob/media/New%20Photos/37651265-7e6e-4e9f-978a-b43704794de9_zpsde657896.jpg.html)
(https://gemstone.smfforfree4.com/proxy.php?request=http%3A%2F%2Fi151.photobucket.com%2Falbums%2Fs160%2FRocksbob%2FNew%2520Photos%2F5939d76e-a960-4eed-9bbb-8a7d37486460_zps14aa60e4.jpg&hash=390a8a715149e9b5f67390417b6bf220) (http://s151.photobucket.com/user/Rocksbob/media/New%20Photos/5939d76e-a960-4eed-9bbb-8a7d37486460_zps14aa60e4.jpg.html)
Here I did my first grind in the process of creating the dome. I ground it at a 45 degree angle down to within about a 1/16" from the base of the Agate. I wanted to have a slight straight side on the Agate.
Side view.
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Top view.
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Here is the next pass around the preform. I went in about 1/2" on this pass.
Top view.
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Oblique view showing the area on top that remains flat.
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Another view.
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This next step is where I start to remove the flat top. Here I go from grinding to a 60  grit slightly used SiC sanding belt. I will use it to take all the needed material off to complete the dome. Because the preform started out rather thin I have to work carefully to remove the flat but still have a complete dome.
Here it is almost fully shaped.
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Another view of the finished coarse sanding.
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Now I start the work on the girdle. I sanded it perpendicular to the top and bottom of the cab.so that the small edge of the Agate will have a finished surface to polish.
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Here it is sanded to a 220 grit surface.
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Next I polished the front of the cab.
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Because I didn't want any of the black from the Basenite to show when the cab is viewed from the front I ground a slight reverse taper to the Basenite, and sanded it.
 (https://gemstone.smfforfree4.com/proxy.php?request=http%3A%2F%2Fi151.photobucket.com%2Falbums%2Fs160%2FRocksbob%2FNew%2520Photos%2F3de5e32a-5515-4f27-b41f-fb623634f8dc_zps68a85141.jpg&hash=132ca2036572e45806acec2b7ec7f241) (http://s151.photobucket.com/user/Rocksbob/media/New%20Photos/3de5e32a-5515-4f27-b41f-fb623634f8dc_zps68a85141.jpg.html)
Another view.
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Next I ground a very slight 45 degree bevel to the back edge of the Basanite layer and sanded it. The purpose of this bevel is to remove any chips that had occurred during grinding as well as providing a safer edge if the cab were to be set.
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Next I sanded the back in preparation for polishing.
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I rechecked the polish on the front.
(https://gemstone.smfforfree4.com/proxy.php?request=http%3A%2F%2Fi151.photobucket.com%2Falbums%2Fs160%2FRocksbob%2FNew%2520Photos%2Ff4f11e1f-f608-4825-8efd-43a7176cec3e_zpse475a769.jpg&hash=d126c802e2f9d197f11e065185823605) (http://s151.photobucket.com/user/Rocksbob/media/New%20Photos/f4f11e1f-f608-4825-8efd-43a7176cec3e_zpse475a769.jpg.html)
I polished the girdle of the Agate and Basenite.
(https://gemstone.smfforfree4.com/proxy.php?request=http%3A%2F%2Fi151.photobucket.com%2Falbums%2Fs160%2FRocksbob%2FNew%2520Photos%2F62dfc85d-acf7-4d9e-a93a-07ee3ce902f3_zps81a2711b.jpg&hash=fe47283b8597f2c3c6b51eefe7fa375a) (http://s151.photobucket.com/user/Rocksbob/media/New%20Photos/62dfc85d-acf7-4d9e-a93a-07ee3ce902f3_zps81a2711b.jpg.html)
I polished the small bevel.
(https://gemstone.smfforfree4.com/proxy.php?request=http%3A%2F%2Fi151.photobucket.com%2Falbums%2Fs160%2FRocksbob%2FNew%2520Photos%2Fd9f41ff2-d2f4-4cfc-83c1-06e6dd8455b5_zps2a5499bb.jpg&hash=9d9f217eaf924f3faa8dc5c11089d18a) (http://s151.photobucket.com/user/Rocksbob/media/New%20Photos/d9f41ff2-d2f4-4cfc-83c1-06e6dd8455b5_zps2a5499bb.jpg.html)
I polished the back.
(https://gemstone.smfforfree4.com/proxy.php?request=http%3A%2F%2Fi151.photobucket.com%2Falbums%2Fs160%2FRocksbob%2FNew%2520Photos%2F39605830-8703-4383-addb-c072c2648b32_zps9176bf3d.jpg&hash=8d0161a48e1c33145d044cc42dc8c382) (http://s151.photobucket.com/user/Rocksbob/media/New%20Photos/39605830-8703-4383-addb-c072c2648b32_zps9176bf3d.jpg.html)
The finished cab.
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Bob

Quite a bit of work, but a stunning cab! The plumes look much better than they ever would on  a 1/4" slab... Thanks for taking us through your process!

Awesome!

Bobby...
I love seeing this step by step version of how you do your amazingly huge cabs.  ura12

Those plumes just jump at you, the basenite was a great choice for backing.  yes16

EXCELLENT! Your precision is incredible. I've always liked you cabs. Nice job! Eric (Ajo)

 That was fun to read and see. I hope people can at least begin to appreciate your expertise and your careful craftsmanship.

Thanks for the in-depth tutorial.  Your right about the backing making the cab stronger.  I noticed that Basenite is often used as a backing and it does look good, but often wondered the difference in visual appearance using a white stone backing.  With the transparency of the plume, would the cab look more natural, or does the black backing give your cab an added visual pop?  

Another thanks Bob for sharing your process with us.  

Great tutorial.....this is usefull for a clear and nice material, thank you for sharing Bob....

Pretty darn awesome Bob - thanks so much for sharing that in thorough detail - things like this help us all a great deal!

Awesome! Love the play by play. I noticed on the last picture, which looks like you took the pic directly over the top of the cab, I couldn't see the bottom of the cab, it was  my understanding that the bottom of the cab should be tapered out from the start of the dome, so the cab won't fall out of the setting?

Jason,
I usually do an inward taper on my cabs so that if or when they might get set the metal will be formed over the taper to hold the stone in place. This one is an exception because of the black backing. When I'm doing an Opal doublet or triplet it will also have this reverse taper to prevent seeing the black backing. To set these stones the bezel will have to be made a little taller so the top edge will form over the top edge of the stone. You have to be a  little more skillful to set these types of stones but it isn't that hard to do. Even though I doubt that a cab of this size or larger will ever be set I still do the reverse taper to keep the black from showing especially if I'm going to be displaying them in my case. On all other cabs that I make regardless of size I do the slight inward taper as if it were ever to be set. I can't imagine who or for what reason someone would want to set one of my really large (4" to 6"across) cabs.
Helene,
I use black backings, clear quartz backings and translucent backings depending on what effect I'm trying to achieve. In this case I wanted to see what it would look like to have a slightly darker background to enhance the plumes. I'm happy with the outcome.
Last week when I was at the CFMS show I got into some in-depth discussions with some of the judges (and judge trainers) about displaying various things. Two years ago I entered a successful case on cabs. One of the things that the rules state is that the largest dimension that a cab can have is 100mm. This excludes most of my cabs from competition in the cabs category. I asked Dee Holland (the guru on judging who is instrumental in writing the rules) why there was this limit and he said it is because in the past some people had ungodly looking huge 1' across "cabs" that they claimed were "wearable" as jewelry so the rules were rewritten to put a limit to such nonsense.
I have always wondered if I could enter my case in a category that was allowed. My case has cabs, jewelry, metal work and carving, a mixed bag of stuff. To my surprise after they looked at the case they said yes! There is a category (I forget which one -  I'll have to read up on the rules to see) and it could be entered as is. I going to do it at the next CFMS show and see what happens. They haven't  found a club to sponsor the 2014 show yet but there are some good prospects, though.   
Bob

"My case has cabs, jewelry, metal work and carving, a mixed bag of stuff."

 acamerashot   Wanna share?

I admire your lapidary skills Bob and enjoy seeing your large cabs. You seem to capture some really capture some really interesting patterns that would otherwise be lost in a smaller cab.
Thank you for sharing your technique.

Thanks for your explanation on choosing backing color.  Helpful you are.  Good luck in your competition entry.  let us know.

Here is what I usually display at the shows. It changes somewhat because I like to display different cabs each time I show it.
Bob
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The work of a true Master Lapidary and Jewelry Artist, well done.

I couldn't agree more, I really enjoy all of his stones and via internet you sometimes for get how big they are.

Yep... I LOVE your gigantic cabs!!!! My little cabmate can't even fit more than a 2" wide surface in it, so I can't go that size, but I totally admire yours!!

Beautiful work as always Bob. Keep sharing those secrets, love them.

David

Beautiful stone and beautiful job, and I love that your back is so finished. That's the hallmark of a real pro.

Debbie K

Great little write up Bob. Just to let you know your web site link does not seem to be wowrking? Might want to get that handled.

Thank you for sharing this Bob, I always appreciate it. I can't tell you thank you for all you share enough!!

I am always in awe with your work, amd I really love and appreciate the way you explain everything step by step.  This doublet is amazing to say the least.  I am not clear as to what you meant in your tutorial when you wrote the following:
" I used a plate of glass and tumbling grit to grind both pieces perfectly flat and then mixed up and applied Epoxy 330 to glue them together."
 In what manner did you use the plate of glass and tumbling grit to grind both pieces perfectly flat?
Thanks for the great lesson.
Stu

Thank you for taking the time to show us how you do that Bob, great pix & tutorial!  yes16

Wahou! Great work, you seems to have some awesome intarsia among that too! Those cabs are stunning!

Stu,
I don't have a flat lap (I used to have one but the motor burned out so I tossed it) so instead of using a machine to get flat backs I just use a piece of window glass and tumbling grit to get the pieces flat. I put a bit of tumbling grit  starting with 220 grit from an old salt shaker on the glass, add a few drops of water and move the piece around on the glass/grit surface in a figure 8 pattern. I add grit as necessary until the saw marks are gone and the surface has an even frosty appearance. I then go to 400 grit and do the same until the pits from the coarse grit are gone and the piece has an even, finer frosty appearance. It is now ready to glue to the other piece that has been flattened in the same manner. I do this with the glass placed in an aluminum tray to contain the grit/water slurry and keep my bench less dirty. The process goes rather quickly because by being able to add fresh grit  it keeps things going right along. With a diamond wheel flat lap the wheel keeps getting duller with use and it can take quite a while to lap something flat.
When I teach about making doublets and triplets I use this method because many of my students don't have a flat lap. This method is cheap and easy.
Bob

I just discovered this tutorial.  Thank you !  You have answered all the doublet questions I've been wondering about and your Plume Agate cab is amazing! 

Not sure how I missed this awesome tut. Thanks Bobby.

One question if you check this again. How does the glass hold up being as soft as it is compared to the agate. It seems like it would wear down rapidly.
Jim

I've ground flats on a mirror before, and it started to dimple in the middle. What's fun is to get a few nice large slabs and use them. I started off with one and used it for 220. When it got smooth it became the 500 grit slab and so on. Eventually you have nice polished slabs as a side effect.

Now that is one hell of a good idea. I have some pretty large slabs that would be perfect. Thanks a bazillion. I hope they are flat.
Jim

Awesome work!  How many years of practice does it have to take to be able to do something this good?  Simply awesome.  I'm new at this so this is really amazing to me. Thanks for sharing this!  ura12

1. With the glass that I use to grind the pieces flat I move the agate or Basenite around to try and utilize as much of the surface of the glass as possible. Each sheet of glass is good for about 10 cabs. I get scraps from the local hardware store to cut up into smaller pieces for this operation.
2. I have been making cabs and such since 1958, doublets and triplets probably only 35 years or so.
Bob

I am impressed by the polished so perfect.
Agata is nice and it shows a very good technique

I'm new here, and to lapidary work. But I know breathtaking work when I see it. The work you've demonstrated here is stunning. And inspiring. Thank you so much for sharing your secrets so willingly and generously. You give us something to aspire to.