Opal Cutting, Treatments & Commentaries

Apr 29 2014Wet Cutting vs. Dry Cutting

During a recent opal cutting class we experimented by completely dry cutting these stones. We did 5 cabochons completely dry (using diamond paste on canvas for a polish) and 5 wet. Of the wet stones 3 of 5 cracked after wetting. All of the dry cut stones finished up with no cracks. In the next class the following month we tried to narrow this down a bit and only roughed (360 grit grinding through 600 grit sanding) the stones dry (frequently using a dry trim saw to cut bits and pieces off instead of using the grinder and avoiding clouds of dust). We did use water sparingly for the 1200 grit and 3000 grit sanding through polish steps with no cracking. Dry cutting is very dusty, but this limited experiment showed the effectiveness of dry cutting. I am now wondering if some of these stone have much amplified hydrophane properties which causes them to absorb more water than the stones silica structure can hold and thus crack. Please let me know how your stones turn out and if dry cutting works for you. Steve 406-651-4947 or vsmithy@bresnan.net.

Tips from Neil in Queensland Australia: I found your website during a Google hunt on cutting tips for Welo. It’s the most helpful and descriptive source on the web in my opinion. I have been cutting the Welo opals dry ever since with huge success. In the last week, after grading, I have cut and pre-polished over 40 opals without cracking. The only cracks are from the ones missed after trimming and drying. I use your dopping method too, using exterior aquadhere which is a more durable pva woodworking glue. Clear nail polish is still needed.

Comments
  1. Link Homepage |

    I can’t remember when actually was the very last time when i saw that great informative article. It should have been a long time ago … Anyhow, preserve the awesome work.

    Reply
  2. shawn cronin |

    Hi there,
    I have contacted you before regarding Ethiopian opal, and had said that dopping with shoe goo worked quite well for me.
    I just recently purchased some more Ethiopian opal in precut cabs, and noticed that, as before, the cabs were cut somewhat poorly with scratches visible through a ten power loupe, along with an irregular surface.
    I had good success recutting the previous batch simply by using a Nova wheel of 600 grit, then a 1200 grit Nova wheel, then, oddly enough going to a 100,000 diamond polish, and even a 200,000 diamond polish.
    My main comment here is that I’ve noticed the Ethiopian opal has wonderful color and movement on what is considered the front (cabbed) surface of the stone, but also has large, bright patches of color on the back (the flat part) often, in my opinion being more spectacular than the cabbed top. My intention is to recut some of these stones into thin, flat ones and simply mount them on a swivel with channel wire, thus letting both sides be seen. My camera has broken and is being repaired, so I am unable to visually document the results. I will start this small project and send you photos when my camera returns.
    Have you tried the shoe goo dopping yet?
    Thanks for having this forum,
    Shawn

    Reply
  3. shawn cronin |

    I live on the coast of California where there is sometimes a wet fog.
    I just noticed that overnight on a night when fog formed, my Ethiopian opals all turned crystal clear.
    They are in a room where I leave the door open at night because, even though we live 7.5 miles from the ocean, we are at 1400 ft. elevation, so the days can be hot, and the door is left open to cool the house.
    There was still quite a bit of color, more than when these same opals were saturated with water as a personal test. I took these opals outside in the sun to look at their color, and some of them started to regain their milky color after 15 minutes in the dryer air (the fog had evaporated)
    I recut all ten of these opals on wet Nova wheels with no cracking, but I saw them all going clear (if they weren’t clear stones to start with) as I worked. Since they were already cabbed, and I was just improving the cut, it did not take very long to do.
    It seems as if humidity in the air can affect the stones in a more “gentle” way than cutting wet or immersing them in water, since immersed stones seem to need a much longer time to recover their natural background color and opacity.
    Ethiopian stones are still a bit of a mystery to me, but, boy, howdy, are they pretty!
    I’ve also noticed that trying to polish these stones with cerium oxide, like Australian opals, will give them an “orange peel” finish that totally destroys the work I’ve done to make them smooth and scratch-free. What a puzzle these opals are!
    “Editor”-Be sure you are using the cerium oxide with plenty of water and prepolish at 3000 grit must also be done with a bit of water for an effective final polish.

    Reply
  4. Dave Jordan |

    I’ve used cerium oxide on a damp muslin pad several times, and a noticed that a week or so later the surface of the stone turned white and opaque. This does NOT seem to be reversible, and I’ve actually had to grind down the affected part of the stone and repolish it. Diamond paste on hard felt or canvas seems to give a good polish, provided you’ve done a good job of sanding and prepolishing, but I don’t recommend the CeO unless you can find a way to use a dry Ultralap (Mylar film.) I also had trouble with opacification when I mixed diamond powder with mineral oil, so I’m using commercial pastes. The pigment that color-codes the mesh size does not seem to soak in to the stones as far as I can tell.

    Reply
  5. Lindsay Koob |

    I have just begun cutting Welo opal (still in the rough-shaping stage), and am curious about Shawn Cronin’s success story above about dopping with Shoe Goo — a product I’ve long used, but just to make my shoes last longer! I’ll be experimenting with different dopping methods in the coming weeks. Right now, I’m about to try Steve’s Elmers glue/fingernail polish method — also, I’ll soon be trying another online blogger’s method using Beacon 527 glue, which entails a brief soak (30 minutes or so) in acetone to get the stones off the dopstick.
    My burning question: What do you use to REMOVE the Shoe-Goo-dopped stones following the cutting/polishing process?

    Reply
    1. Shawn Cronin |

      Hi,
      I haven’t been back to this site for years, but I simply peel the shoe goo off with a fingernail or a small stick. I think it’s important to leave the stone dopped for the shortest time possible since shoe goo is solvent based and will get harder and more tenacious within weeks. I usually leave the stone on the dop stick for only a day or two, so it’s still rather flexible when I go to remove it.
      I just last weekend purchased a few wonderful Ethiopian cut stones to put on swivels and the dealer gave me a piece of rough. It was snow white but when I cleaned off the skin with a wet wheel it became clear within minutes. As clear as glass with absolutely super brilliant colors. I ground away the cracks and put it aside and the next morning it was snow white again and the color was virtually impossible to detect. This particular stone is the most hydrophilic stone I’ve ever seen. It sticks to my fingers! When wet it gets clear in just over a minute. The color is still there when clear. It also dries quickly- in about ten minutes.
      So- how should I treat this stone, any suggestions?

      Reply
  6. Kelly |

    First time cutting boulder opal today. Actually first time anything with any opal. Was leery because of visible fractures. Thanks to your website I dry cut and had only minimum increased fracture. Thank you!

    Reply
  7. john |

    my method for the dry cut, I wait until I have 10 or 15 stones to work with, then cut on them for a few min each only, seems to work as none have cracked or developed any anomalies since doing it that way. They are beautiful stones and different from aussie stones, so should not be compared I feel.a few I polished on the natural lines as I got them after cleaning off any matrix and wire wrapped them. They get comments all day long

    Reply
  8. Larry Sklar |

    Interesting array of opinions and experiences. I’ve been working with the Ethiopian material since ’09, and discovered its bizarre properties through a lot of trial and error. I was flipped out the first time I worked with this opal and saw it turn clear as it absorbed water, and equally flipped out as the finished stone turned milky white, and then returned to its original body color and translucency as it dried out over the next several days (or sometimes even longer). It is a dynamic stone that has its own life! I have found that sticking with a simple cutting process works best:

    I use lots of water, and, yes, a good portion of the stones (30% – 40%) crack upon initial hydration. I think it is far better to “beat it up” at the onset, because once the stone has cracked and been broken into its separate pieces, I have not had ONE stone crack or craze after it’s had the final cut and polish.
    I use plain old green dop wax on a wooden dowel, getting the wax dripping hot, and have not had stones crack during the dopping process. I think glue, expoxy, etc. is overkill and unnecessary.
    I use a progression of wet Nova wheels (600, 1,200, 3,000) for sanding & pre-polishing, and polish on a damp leather disc with a French cerium slurry.
    I put the mounted stone in the freezer for 2 minutes to remove them from the dop stick. After taking them out of the freezer, they typically drop right off the dop stick or easily come off with a little prodding.
    I have not experienced the lemon-peel effect, but definitely know that you have to be very diligent to avoid flat spots.

    My concern with dry cutting is this: What happens when that beautiful stone you cut is mounted in a ring, and that ring ends up in water (bathing, swimming, showering, doing dishes, etc.)? Or what if it’s exposed to a high humidity? My bet is that some of the stones may crack as they hydrate, and that is a big bummer if the stone is in a piece of jewelry! Hence my philosophy of beating the stone up during the cutting process, because if it makes it through that, then you’re home free to a stable stone! Think about it: if these amazing stones can absorb water (often up to 10% of their weight), dry out, and do this again repeatedly without cracking or crazing, as the finished stones can do, how much more stable can you get?! The anti-Ethiopian opal naysayers (typically Australian opal dealers) will try to convince you that Ethiopian opal is not stable: don’t believe them!! Over time, I believe it will prove itself to be the second-most stable type of opal (after boulder).

    I’ve heard a few stories of Ethiopian opals turning milky and not regaining their original body color and translucency, but I’ve personally never experienced that. If you let them dry long enough after cutting, I believe they always return to the original state.

    I can relate to what Shawn said about the “back” often being as nice or better than the “front” of the cab. With this material, the color is often through and through the stone. I often end up with stones that are polished on both sides, as I couldn’t decide what would be the front and what would be the back – they’re sometimes equally beautiful, sometimes with different patterns or colors.

    Happy cutting everyone!

    Reply
    1. Alfred Trevisan |

      I have been cutting Australian opals for more than 20 years and just started to cut Welo which cracked every one I cut after. I cut them the same as I cut Australian Opal with water and I am looking forward to tomorrow to cut some in dry conditions hopefully it works. With respect to the dopping I have been using MEGAPOXY PF it is a 2 pack, using Faceting dopping sticks. Very easy to take the stone off, Just warm the brass dopping stick on a candle and pull the stone off before any heat transfers to the stone. I do a lot of faceting so it need to be nice and steady.

      Reply
  9. vsoadmin Post author|

    Secondly, I’ve FINALLY gotten my lapidary workshop set up & running in my new home … after some trial-and-error as to where I should put it! I’ve also upgraded my equipment (variations on the flat-lap-based High-Tech Diamond brand) — i.e., I now have new “smoothing” discs in four grits (325, 600, 1,200 and 3,000), all backed with thin rubber foam pads to minimize “flat spots” and facilitate doming.

    I’ve also found that a 600-grit grinding lap is quite sufficient for basic shaping of stones (unless you want to quickly grind away sand or potch layers) — and it leaves relatively smooth and scratch-free stone surfaces that are much easier (and faster!) to smooth out and polish.

    Speaking of polishing, the Hi-Tech setup uses felt pads (also foam-backed) that you charge with diamond polishing compound (I use 14,000 and 50,000 grits) — and it’s a strictly DRY polishing procedure (though you have to be careful to avoid undue heat buildup).

    FYI, I’m still using the “damp” smoothing and polishing technique (neither wet nor dry) that I described to you earlier: namely using a sponge (or a VERY slow water drip setup) to keep the smoothing disc just barely wet. It eliminates the dry-cutting rock dust problem AND minimizes water absorption into the hydroplane stones.

    I’m also experimenting with dopping my stones with “Beacon 527” glue: it holds the stones very tenaciously, and requires only a brief soak in acetone (outdoors!) to remove them after cutting. Interestingly, the acetone also soaks into the stones, and causes the stones to lose color like water does … BUT they dry out MUCH more quickly, and don’t dim the play of color or damage the stone in any way. I haven’t tried it on my larger A – to – AAA-grade stones yet — but it works very nicely with smaller stones. It also seems to minimize the cracks that often show up when you soak the stones in water. Lindsay Koob

    Reply

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