I'm Looking For Backing & Capping Material - Slabs Actually

Well I just learned something. I didn't realize Basanite is "a pure BASALT with no pitting/crystal pockets, crystal inclusions or voids".

Also black India agate. I got some from the living estate I was at a week ago, haven't cut any yet. I have basanite and some softer stuff called argyllite that is black as well, not sure for sure where it is. I also have a little man made quartz in chunks and thinner slabs.
If you want to PM me I can probably find you a sampler to get you started anyway from the stuff in the cabbing area. It will range from .100 thick to .150", I tend towards thinner with the black and a little thicker with the quartz.
Do you have a lap to get the surfaces flat? That really helps with backers and caps. I get nice flat parallel slabs in my saws, but they still look a lot better if they're a perfect match.

Try looking for some black chert. That might work and should be low priced.

Thanks Rich! 

Maybe I'm not searching the right terms...but I haven't been able to find a ton of info on backing material. Thanks for letting me know about this option! 



Thanks Lee!!

Woot Woot! I'll shoot you a PM here in a little bit!!

Thanks for letting me know of some optional material as well. I do have a flat lap (slant cabber) as well as a flat disk on the end of the arbor on the cabbing machine...so I should be able to work the pieces either way.

That makes sense to go thinner on the black and thicker on the quartz. The backing doesn't really need to be thick by any means...




Thanks James! 

Those could be some more optional materials.

As far as what other specific colors...I have nothing in particular in mind. I was kind of wondering what colors people had out there. I do know there's a technique of using colored foil in between the backing and the main material...which adds an interesting perspective and options for colors. 



Thanks Beth!!

Another great "affordable" option!! 



Thanks Tela! 

It didn't occur to me to use actual glass! Duh!! I should go back through his threads and look at some of his stuff. Now that you mention him, I do remember seeing a bunch of his doublets quite awhile ago. Thanks!! 

Thank you so much Victor!

I'd definitely like to take you up on that offer!!

Thanks for this Lee! 

I've seen a couple ways using the top edge of the backing material as reference. If I remember correctly, BikerRandy would take the top stone clear down to the backing material on the edges. I've seen others done where it isn't clear down to the backing material. I suppose some of that has to do with the thickness of the backing material...

I figured when I wrapped these, I'd allow the wire to create a definite "bezel" edge...as opposed to some wraps where the edge of the cab can be seen in places.

Thank you SO much Gary! 

I remember hearing black jasper being used now that you mention it! (That's how my memory apparently works...I "remember" when someone brings something up again! LOL)



I had no set idea on a specific weight per se. Can you ever have "too much" of anything rock related on hand? LOL - Obviously 100 pounds of slabs might be excessive...but a couple pounds in slabs wouldn't be a bad thing to have laying around.

I don't think you're wrong about the $20 per pound for slabbed material being a fair price...especially when I know I don't have the ability to get consistent 1/8" (or so) slabs on my saws...

Back in the day, for black backing material, a fossilized wood material "Jet" was often used as backing for opal doublets and triplets. Jet was near the same hardness as opal so was a good choice. I used to see Jet rough pieces and thin slices all the time at shows but it doesn't seem to be nearly as common now.

For Turquoise 78 LP records were often used. They were a little thicker than the 33 LPs. Just glue a piece of a broken LP to a relatively flattened back of a piece of turquoise and grind the cabs pre-form shape. When JB Weld and Devcon became available those were used for backing as well. Especially for pitted or uneven back surfaces of turquoise. One would have to be careful using anything that heats the turquoise. Natural turquoise can loose it's color if gotten too hot. And any turquoise stabilized with resin doesn't like being heated too warm either.

For everything else black onyx, black nephrite and black basanite were the most commonly used black backing materials. Not sure how available it is these days but black Wyoming nephrite was fairly common and inexpensive back then. The Wyoming material had a beautiful fine grain as well.

These days as someone else mentioned black glass is sometimes used for backing. And clear sheet glass has been being used commercially as capping material on opal doublets and triplets made overseas since at least the 1980s. But most glass scratches more easily than quartz. So for ring stones or bracelet stones, IMO quartz is the better choice. Natural clear quartz is easy to find but you usually have to work around fractures, veils and other impurities. Large synthetic lab grown quartz boules are much cleaner and used to be fairly common at shows too. But I don't see those around much anymore. You can still find optical quartz (glass) rods though.

And I remember that there used to be a company which produced iridescent ammolite doublets using clear synthetic spinel for the caps. Spinel has a MOHS hardness of 8 so it is tougher than quartz and ideal for ring stones that are subjected to a lot of wear and abuse.

Interesting topic Jason! I have it in mind to play with some doublets too at some point. I’ve found a handful of gorgeous but too thin slabs in my stash. I recently cut a cab that was already prepped as a doublet. Mahogany obsidian with I believe man made quartz or glass on top. It cut well and I did notice that the transition line would be a good spot for the bezel setting. If you strike out on finding black material, I have LP’s! 🤓 Looking forward to seeing your work!