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Friday, November 4, 2011

What I Look for in a Stone: Part 5, Durability

Part 1, part 2, part 3, part 4

This post will be a little different. Instead of a bunch of pictures, I'm going to discuss durability and include a few (test) videos that I made with my camera. Sadly, my actual video camera is terrible for close up.

How a stone will hold up to a certain wrap is a big consideration. Not only do I not want to damage a stone, I also don't want all that time and work gone to waste. A good example would be of a stone I recently set. It is a Candy Stripe opal or Bacon opal (yeah, I know, dumb name). Here is the stone before I wrapped it.


Here is the stone after a simple wrap.


OUCH! I had never worked with this kind of stone before and had never had problems with any kinds of opal before, so I wasn't as careful as I could have been. However, the way the corner just crumbled, I think it is more a matter of the stone being very soft, than my being too rough. 

Deciding which kind of wrap to use, is also a consideration. With the opal, if I had done a loose type of sculpture versus a tight border wrap, it may have held up. One has to also consider whether or not it is going to be a wrap which has lots of sharp ends. If so, one had better file those ends, because some stones can't go in the tumbler- namely malachite. The polish on a malachite usually suffers from being in the tumbler. I have been told by a few reputable sources that ZAM polish works to bring back the shine, though I haven't tried it, yet, myself.

In a previous post, I mentioned rainbow hematite. It has been, hands down, the most delicate stone I have used to date. There are only a few ways it could be wrapped. It is a type of druzy, though one like you rarely see. Most aren't even suitable for jewelry. Another great, natural druzy is the green garnet, uvarovite. Druzy or drusy stones take a lot of care in setting and wearing. I approach every one on a case by case basis. The video below is of the stone in the picture that I linked to. It is so bright that it is hard to see the color in the video. Just imagine that all the sparkles encompass the color of a rainbow, hence the name.



Then there are the stones like mystic topaz that have an easily scratched surface coating. Likewise, the titanium coated druzies scratch real easy. Honestly, I don't even use these stones, because, although beautiful when new, they can look pretty bad, real quick, if not taken very good care of. But, that's just my opinion.

Some stones do not take a good polish. Some lapidaries put an epoxy coating, like Opticon, on them to produce a shine. These stones are often soft, too, and the surface may have minute pits that needs to be sealed with the epoxy. I have seen this treatment on serraphinite and on my newest stone purchase of rare, Russian fuschite. It is also on my astrophyllite (see videos) With this treatment, the stone is coated, to produce shine and to seal. These stones, I won't usually tumble, though some of them I will, like ammolite. Natural ammolite are often given a coating of Opticon to protect it.



(This is the first video I have done for the web and it was one helluva challenge! I deliberately made this dark and light because I couldn't decide which looked better for the sparkles. :)  I should have done this for the last part of the series!!)



There are stones like turquoise and variscite that are soft, too, but because most are treated to produce a more durable cutting material and cab, I don't have a problem with them. However, many of the stones have a soft matrix that can be tumbled out of them. This creates an undercutting of the matrix, resulting in an uneven surface. (or worse)

Some stones are backed. A backing, often of quartz or basalt, can be added to a thin or delicate stone to produce a more durable cab. These stones are like doublets- only backwards. With a doublet, a top is added instead of a bottom. Usually clear quartz or created spinel is used. The clear top also magnifies the colors in the stone. This is one reason why you often see them on opals and ammolite. I've never had a problem with a doublet or backed stone, so long as they were made correctly. If you purchase a doublet, check with a loupe or magnifying glass for tiny bubbles. There should be none, or, at least, very few. Bubbles can eventually destroy the stone because as the top gradually loosens, it often takes a layer of the stone with it. I have only seen this happen twice, though. (Both on ammolites!)

The question that I have most often been asked is, "Do you tumble opals?" My answer? A resounding, "Yes!"  If you take a look at what an opal is made of and the vast variety of them, you can get an idea that it is pretty hard. (keyword being silicate) I can't make any blanket statements about opals in general, but for the precious opal that we most often think of- the colorful, white ones and the crystal ones- they take a great polish and are hard enough to tumble. Koroit, boulder or matrix opals are hard, too, but I take a good look at the overall stone before I tumble, making sure that the matrix can take it. There is no science to it, I just eyeball it and rely on experience. As for wrapping, I would use any wrap on any opal- except candy stripe opal. So far, that has been MY experience and I offer no guarantee or warranty on it. :) I think people are worried about opals because they appear so delicate. Now, as a caveat, I have to say- don't bother wrapping a cracked or crazed opal. If you have seen one, then you know what I mean. The words are perfect descriptions. Don't use them. They will not hold up to either time or a wrap.

In closing, I reiterate that there are few stones that I won't wrap. However, there are some that take special care like druzy, soft stones and coated stones. If you ever have a question about a stone's hardness, go to Mindat.org for all the info you ever wanted and more. The hardness of stones is listed right at the top of each stone's page. If I have left something out that you wanted to know, specifically, leave it in the comment section :)

5 comments:

  1. Well done. We think quite a bit alike about the stones to tumble. I've even tumbled good pearls. The caveat is that it has to be a "good" pearls. Most sold in the market can't be tumbled because they have so little nacre on them. I surely don't tumble long though. Just to shine up the metal.
    I've never seen Candy Stripe Opal. It looks amazing and it's sad that it's too soft to wrap. Love the series. Hope you'll keep it up.
    Lois

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  2. Hey TelaT, Great segment. I feel much more knowledgeable about stones after reading this series. The addition of the videos bring the stones to life with their sparkles.
    Thank you for taking the time and energy to share this information. I too hope you will keep up this well written and informative series. There are so many amazing stones and so much to learn about them.

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  3. Hi Lois! Yes, I tumble pearls, too. I've had some cheap ones bleed out their color, too. Sometimes, I tumble a piece all night long if it has a lot of ends. But, not too often, though.

    Thanks for the support. :)

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  4. Hi Christine and thank you :)

    I wanted this series to be about the stones and what they look like versus their chemical make up or metaphysical healing properties, because how they look is what attracts us to them in the first place. I'm down to the last segment, though and that would be Cost.

    I'm really glad you enjoyed this! I was tickled to death to learn how to post a video. Maybe I'll do a few more of the splashy stones with video. :)

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  5. Love the info... I am learning a lot from you.. Thanks Tela.. Also the gem video is neat... Lynn

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