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December 10, 2018, 09:01:19 am
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What to use to back a cab?

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Author Topic: What to use to back a cab?  (Read 2024 times)
mdfa.ca
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« on: November 03, 2014, 05:11:39 pm »

 help

Hello everyone,

Here's a question that has me stumped. I received a custom order for a pendant to be made with the client supplied cab of golden rutilated quartz, set in sterling silver.  A beautiful stone. The client has requested the stone be set on a black background to show off the gold needles in the cab. So, here are my 4 possible ways of doing it (that I can think of):

Option 1:  colour the inside of the setting with permanent marker.
Cons: Not sure how permanent this is. I think it would be ok as long as the pendant never gets wet or cleaned. I'm worried that if the client ever got it cleaned, the coating will degrade.

Option 2: piece of black paper behind the cab.
Cons: could it shift and even squeeze out from behind the stone? And should the pendant become wet, paper would pretty much dissolve.

Option 3:  piece of black plastic (like form a garbage bag) again, behind the stone.
Cons: plastic being slippery it probably has an even better chance of either shifting behind the stone, bunching up or slipping out. Also, I know plastic will degrade over time so it could start shredding in a few years.

Option 4:  a piece of thin felt from a craft store.
Cons: I'm not sure... How long does felt last? What would happen to it if it became saturated with jewelry cleaning solution? It would also add quite a bit of height to the stone.

I'm sort of leaning towards Option 4 but I feel I don't have enough information to truly make an informed decision.

What do you guys think? What is the best option? Are there any other I should go with?
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gemfeller
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« Reply #1 on: November 03, 2014, 06:05:34 pm »

Another option would be to blacken the inside of the setting with liver of sulphur. 

Yet another would be to mix lampblack (candle soot) with epoxy to blacken it and coat the back of the setting with it.  That would probably be the most durable way.

Rick

 
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PhilNM
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« Reply #2 on: November 03, 2014, 06:32:57 pm »

Use what we turquoise folks do. Basanite or basalt.  sliced real thin. IT takes a polish, so when you're donre you can polish the back a bit.
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itsandbits1
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« Reply #3 on: November 03, 2014, 06:42:05 pm »

all good suggestions and another is some black jade
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« Reply #4 on: November 03, 2014, 06:49:04 pm »

I think the black resin may be best. adding to the stone height even slightly seems to be undesirable. the basanite or jade would be thicker than felt.

I gathered the back was to be sheet silver, so having a material that polishes is moot. the liver of sulfur was my 1st thought, but it would not be immune to jewelry cleaner.

a good quality resin with lampblack would be thinnest and most durable
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rocks2dust
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« Reply #5 on: November 03, 2014, 09:06:03 pm »

Doing a doublet with basanite, black jade, or similar would stand up the longest, but something like black mylar or lamp black would also work if the client doesn't mind taking extra care when cleaning and is aware that it might need to be rebacked at some point. I'd avoid things like permanent marker (changes color over time) and many plastics/resins that, once the stabilization additives lose their effectiveness, eventually release acids that destroy silver (e.g., PVC-based and others many of which will migrate into the silver causing "silver disease" that is almost impossible to stop once it starts). The Canadian Conservation Institute has some online resources that would be good to consider when creating jewels (such as this piece on long term storage of silver objects).
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deb193
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« Reply #6 on: November 03, 2014, 09:22:57 pm »

good point about acid release - but aren't there conservation grade resins?

maybe best after all to design a setting that can tolerate a 2mm stone backing.
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PhilNM
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« Reply #7 on: November 04, 2014, 09:42:10 am »

Another good one I use all the time is JB weld. Sets up hard as steel, and you can make it as thin as you want. I typically smear the back of a cab with it, then press it down hard onto a piece of flex plastic to get it as thin as I can. 24 hours later, I peel it off the plastic and off to the grinding and polishing wheels we go.
I also use basanite (aka black jade I'm told)  slabbed at 1/16th inch, and it's strong as steel also. But if you're going to cover the backing with silver, your best bet is the JB Weld, which dries dark dark grey.
Maybe an old phonograph record, then ground thin? Bit I'm not a fan of this method. I have a friend who uses them for all his backing, and while he has excellent cabbing skills, I just don't like the affect/effect of the vinyl.
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finegemdesigns
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« Reply #8 on: November 04, 2014, 10:39:32 am »

I use Black Jade Actinolite to back turquoise. The only problem is getting the slab saw to cut these super thin slabs with consistency. The ideal is probably 1mm-2mm. I will be retrofitting my 10" Lortone soon with a new tight vise carriage so should be able to offer these thin slabs again on eBay. One thing to keep in mind is that there is a huge loss of material when slabbing this thin. You lose as much weight from the saw as you get in slabs.

http://www.zbestvalue.com/LabReports.htm

http://www.finegemdesigns.com/blackjadesnavigation.htm
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« Reply #9 on: November 04, 2014, 10:51:54 am »

good point about acid release - but aren't there conservation grade resins?
It is difficult to tell when the ingredients of proprietary compositions are likely not to be labeled. When they are, chlorine, sulfur and similar compounds are warning signs. Organic compounds can also change over time as the ingredients slowly interact. Because of the short marketing cycles for these products, the only testing is going to be laboratory "accelerated aging" (which seldom accounts for the breakdown of stabilization, anti-oxidation and/or anti-UV additives over time). By the time real life 10-20+ years testing results come in, the product is almost always long gone from the market.

Another possibility would be thin black glass (1-2 mm). If you have access to a kiln, you might also consider fusing black enamel powder to the back of the setting. Either would be long-term stable. Enameling is something I've always wanted to do again. I know you are supposed to also be able to fuse the enamel using a torch, but have never tried that. Has anyone here done enameling with a torch?
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« Reply #10 on: November 04, 2014, 11:41:32 am »

We tend to think of black for a rutilated quartz stone but there are other very unique backings. I know of one jeweler who backs his rutilated quartz with deep blue lapis and the result is stunning.  On the other hand, a simple and quick solution which I have used is colored fingernail polish.  I have one stone which is commonly called garden quartz which contains many inclusions including rutile which I backed with dark green polish and it is pretty special.
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mdfa.ca
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« Reply #11 on: November 04, 2014, 12:42:45 pm »

I wanted to thank all of you who have replied to my query. You have pointed out some other pitfalls with some of the materials that I did not consider and offered me many more options. It would seem I have opened a pandora's box LOL.  I thought resin was a good idea but yes, the chemicals in resins are a big unknown so I think I'll let that one go. The idea of creating a doublet is a tantalizing one and would solve another problem:  as I was looking at the stone in more detail, I realized it's cut unevenly. It's shaped as an elongated shield and when you look at its profile from the long side, you notice the pointier end is a lot lower than the rounded end. Hmmm, I'm sure making a doublet would allow me to even it out with some creative polishing. But, and this is a big BUT, I have no experience with making them whatsoever and given that this is not my cab but supplied by my client, I am very cautious of learning on it. So I will have to pass this time.

Not too keen on the nail polish either, simply from personal experience. When I put it on my nails, it lasts about 1 day so I am doubtful it is going to last years in a piece of jewelry.Which leaves me with two options:  black enamel (I do have a kiln) but it would not solve my problem of crooked stone, or JB Weld (would have to see where to get it.) I don't really want to attach it to the stone itself, but if this product is what I think it is, it should not be a problem to mold it in a way that will compensate for the irregular table of the stone.

Hmmmm, now that I thought about the JB Weld, I just had another idea... Black polymer clay! I can't believe this hasn't occured to me from the start. I can mold it right inside the setting and bezel to compensate for the stone height and bake it right in, at which point it should become inert. Does anyone know if that would be safe for the silver and the stone?
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mirkaba
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« Reply #12 on: November 04, 2014, 01:14:44 pm »

I use Basanite for doublets and triplets. I have been using black electricians tape for backing/padding on crystaline Opal with good luck.
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« Reply #13 on: November 04, 2014, 01:33:01 pm »

I have noticed that with doublets that the cab really "pops" once the basenite is epoxied to the cab. Prior to epoxy  you can hold the cab on top of the basenite and get a general idea of what it will look like, but it looks way better once it's glued. I think it is because the epoxy fills in any tiny gaps and  the light transmits all the way through the cab

I am mentioning this since you are talking about using felt, paper, or plastic. I don't think it will have the look as good as something that is actually bonded to the stone like, basenite or resin.
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« Reply #14 on: November 04, 2014, 01:54:30 pm »

What kind of epoxy does one use for gluing the cab onto the doublet?
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