Lapidaryforum.net
Let's Rock => Rock Talk => Topic started by: Rosemaryr on April 06, 2019, 03:46:21 PM
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I have mostly been working with some of my dad's stock of turquoise, and now have been contemplating doing the thinner pieces. I know that many people often use some kind of (black, usually) backing material for the thin slabs. What is that material.. where can I get it... is there a commercial name?? ( I *think* I have seen a few references to Liquid Steel, but really?? Is that what it is?) Any info gratefully welcomed!
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I have mostly been working with some of my dad's stock of turquoise, and now have been contemplating doing the thinner pieces. I know that many people often use some kind of (black, usually) backing material for the thin slabs. What is that material.. where can I get it... is there a commercial name?? ( I *think* I have seen a few references to Liquid Steel, but really?? Is that what it is?) Any info gratefully welcomed!
Liquid Steel is an epoxy with powdered metal mixed in. You can find the stuff at hardware stored, auto parts stores, etc.
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I just wasn't sure if that was the material used, or not... I thought there might be an actual lapidary oriented material (resin?) that was being used.
It just seemed like it was the only stuff that fit all the parameters: black, putty-like, gap-filling, capable of being shaped while wet, sets hard enough to grind and shape, solid enough when dry to support the thin material.
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Basenite is used for backing thin slabs. Works well with clear agates to show off plumes or other inclusions. But its a stone, not an epoxy or putty like material.
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Basenite is used for backing thin slabs. Works well with clear agates to show off plumes or other inclusions. But its a stone, not an epoxy or putty like material.
Yup, that's traditionally the stuff. I always question whether any epoxy is going to be rigid enough. The whole idea of using basanite is that it is rigid (if it can be bent even slightly, then it isn't adding much to prevent the turquoise or whatever from cracking) with a tough, fibrous crystalline structure. Another tough stone backing would be nephrite jade - especially if you are making a double-sided cab.
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Yes, but making a doublet cab requires the top piece to have a flat side to match the backing material. Much of the thin turquoise I have, is irregular on it's back side... requiring the backing material to mold to it for proper support. And if I grind the back of the turquoise flat, then there isn't much left to work with. Most of it is already only about 2-3 mm thick, and it's going to be hard to just smooth off the edges without losing precious material.
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The material I have seen uses an epoxy for that exact reason, filling voids and uneven surfaces on the underside of turquoise too thin to make a free cab but outstanding material none the less. I have never known which Epoxy people have used. I have tried Jbweld and it was decent but not quite perfect. I think the Liquid Steel is more the material. The epoxy had the shiny metal surface when polished that Jbweld did not give. The best result I have seen is Devcon Steel Epoxy. A bit pricey but works well.
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Yes, but making a doublet cab requires the top piece to have a flat side to match the backing material. Much of the thin turquoise I have, is irregular on it's back side... requiring the backing material to mold to it for proper support. And if I grind the back of the turquoise flat, then there isn't much left to work with. Most of it is already only about 2-3 mm thick, and it's going to be hard to just smooth off the edges without losing precious material.
I think you may be confusing terms? What you are calling "backing" is what I've only heard of as "filler" (except in a few cases where the epoxy actually is the only thing used on the back - usually just to make the stone thicker - not to make it more sturdy). A doublet using another stone as a backing does not have to have a completely flat side - the epoxy can fill voids between the roughly flat back of the gemstone and the basanite or other actual backing. Most any epoxy that doesn't soak into porous stone would do.
The only doublets that require a perfectly flat side are those that have a transparent material bonded to the front.
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I have had good lunch with JB weld on thin turquoise. But I have never tried liquid steel so don’t have any experience. I will have to try it next time
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Thank you all, for the information. I will have to give these suggestions a try. I don't think my skills are ready enough for doublets, but I will keep the information in mind for the future.
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Well, the consensus, over at the turquoise forum that I attend, is that Devcon is the material of choice for most high-end turquoise backing, with a few middle price-grade options added. It's expensive, but looks like it is worth the expense.
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you can also use auto body filler.
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If you ever want to get really "fancy" with your epoxy backings colorants are available. Another option is to grind tiny useless chips of similar material to a powder and mix them into the epoxy. An epoxy with a longer working time will be more forgiving.
Find a plastic bottle cap or such just a bit larger than your stone. You'll have to cut or grind it off later. Put your epoxy/colorant mix in, then your stone. Put some of the epoxy mix on the back of the stone first to help prevent air pockets. Small bubbles won't be an issue for opaque stones - you just don't want big pockets that might make it weak.
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There's a form of epoxy available from RioGrande called Colores™ Epoxy which works well for this. You can also purchase it in a bunch of different colors. It's pretty cheap for the volume you get. It sets up hard, but I believe it takes 24 hours. I recently used this on some thin turquoise. In this case I mixed some of the colored forms until I got close to the color of the natural turquoise. This way on the chance that some of the epoxy showed over the bezel of the setting it would not be an eye sore.
Generally I used this by pouring it into a small plastic mold (egg cartons work well) to a decent thickness. Then I kind of "settle the stone" in place so that the epoxy fills into the crevasses and holes in the stone.
330 epoxy also works well, as does J-B weld epoxy.
As far as backing stone, basanite works well, sometimes I use black obsidian (though it's more fractious). I've also found that if you have any places nearby that make stone countertops you can poke around in their trash bin and find all kinds of colored stones that can be used for cab backing if you like.
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I don’t like the idea of using epoxy, so I’ve used basanite and black jade when I’ve backed opal or labradorite and I’ve used Hxtal to seal them together. For opal, Paul Downing recommends (in his book) sometimes painting the back with a thin layer of black or adding colorant to the epoxy.
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If the back of the stone is extremely irregular, it will need to be filled to at least a point where you would have a flat enough surface to add the basanite/nephrite backing.
If coloring the epoxy, Hxtal is an unnecessary expense since it's just a type of epoxy that yellows less than others.
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Coefficient of thermal expansion is important since you would prefer to have 2 materials that are bonded together to expand and contract at the same rate with changes in temperature. Either that or you could have a binder like epoxy that sets up NOT rock hard like super glue does. It could be possible to have turquoise break if it is bound with rock hard super glue to a material that has a highly different coefficient of thermal expansion.
I like to use black jade actinolite thin slabs with epoxy 330 since this epoxy has a very slight flexibility which allows for differences in thermal expansion.