[Jewelry making - Article 00150] - Re: [Orchid] Strange opal experience (long explanation)

[Douglas Turet]

========[ Invite a Friend - http://www.ganoksin.com/invite.htm  ]========


>         After further checking, we find that she purchased it for
>     about $200.00 on a cruise. We would have estimated the value to be
>     much higher, based on visual observation. The stone weighs 1.02
>     carats. It has a dark brown body color, with very good play of
>     color- large, distinct flashes of red and green." and: "Here is the
>     weird part: when David got the stone wet during cleaning of the
>     finished piece, it turned very dark and lost its play of color. We
>     had the ring soaking in warm ultrasonic solution, though the
>     ultrasound was not running. The stone looked dark when we dried it
>     off, but then  returned to its original appearance within
>     approximately 5 minutes. It also seems softer than regular opal,
>     with the finish being disturbed even with routine, careful
>     polishing of the metal around it. We have never seen or heard of
>     anything like this. Have any of you?" 


    Hi Brenda, Yes, I've heard of this, and dealt with it a couple of
    times, too, but not recently. What I think your customer may have
    bought was a cheap piece of Mexican Opal that had been "barnyard
    burned" into its present color. Although there are other types of
    Opal that'd also yield a brown body color and bright plays of color
    (sugar-&-acid _treated Andamooka Matrix Opal, the Koroit Coprolites
    and the new Nigerian Opals are but a few cases in point), the
    "disappearing fire trick" leads me to believe that the former is the
    culprit, and here's why I think so. You see, back in the mid-to-late
    1970's, an awfully high percentage of the Opal rough produced by the
    mines in Queretaro, Mexico, came out of the ground as the usual Fire
    Opal -- i.e., a translucent to transparent Opal in firelike colors
    of orange to red, with or without the spectral play-of-color most
    jewelers think of, when they hear of an Opal's "fire" -- but quickly
    dehydrated to an unattractive and frequently crazed/cracked,
    peach-to-salmon colored potch, called Hydrophane, which is unusable
    for jewelry purposes. 

    In order to really understand this "odd duck" stone you've
    described, you really need to examine what Opals are about, as a
    group. Precious or otherwise, Opals contain trace amounts of water
    within their structures, which, in turn, are comprised of
    densely-packed, non-crystalline masses of silica spheres, called
    "Crystobalite spherules"; in essence, a semi- to mostly-petrified,
    hydrated silica gel. Get a piece with a low water content (say, 0.25
    to 1%), and with these spherules precisely stacked in a
    size-graduated order, and you wind up with a crystal-clear chunk of
    Precious Opal with "#5" level play of color (the brightest
    possible). Increase that water content to 4-5% and the body of the
    stone becomes cloudier, or opaque; jiggle the array of spherules a
    few times during their growth process (seismically), and your play
    of color dwindles, as well. 

    In most cases, this water content is fairly low, and the more stable
    Opals (like many of those from Mintabie, Australia, and Piaui,
    Brazil) bear evidence of this. At the other end of the equation, we
    come to Hydrophanes, which have _so_much_ water in them -- often as
    much as 8-10% -- that they ofen will dry out and crack while being
    taken out of the ground, or soon thereafter, and are so unstable
    that they're often only available as specimens, packed into a jar
    with some sort of colorless fluid, forever to sit atop your favorite
    bookcase! (Probably the best examples of this are the partial
    replacements of wood, found in the Virgin Valley area of Nevada.
    According to some reports I've heard, some of these Opalized woods
    are still "woody" enough to burn as firewood, once dried.) Anyhow,
    Opals from the group, while often among the most beautiful, when at
    their best, are usually so "thirsty", when dry, that they will
    actually stick to your tongue as tightly as a leach, if given the
    chance. As such, a great many attempts were made to try and
    stabilize them, in hopes of realizing silk purses from sow's ears. 

    Probably the most easily done of these, and the one I suspect was
    responsible for the piece your shop handled, was one which involved
    first cutting the stones to their approximate finished size, then
    completely drying them out, first in the sun, and later with a
    chemical dehydrant. Next, the stones were immersed first immersed in
    a solvent-laced then bath of ordinary motor oil, then set to "burn"
    in a pile of decomposing horse or cattle dung, where it sat for
    several weeks before, finally, receiving its polish. A good number
    of similar stones then entered the stone market, and were sold under
    names like "South American Black Opals" (origin frequently unknown)
    but, because the original, untreated, material was so structurally
    unsound, I doubt that many of these "barnyard burned" Mexican Opals
    still exist. 

    The one key detail that "tipped me off" about your customer's stone
    was the fact that it lost its color in the soapy solution in your
    ultrasonic tank, even though "the ultrasound was not running". 
    Because of the oil fillings in their microscopic pores, these
    particular Opals had the "un-Opal-like" tendency to repel water,
    rather than absorb it. The only way to overcome this property would
    have been to dissolve these carbon-laden oils from the outer
    surface, which, in turn, would have left your bench jeweler with a
    stone whose outer "skin" was now saturated with a soap, whose
    density/opacity, in turn, prohibited the play of color from shining
    through. Once dry, all of that "fire" would again transmit from the
    stones subsurface (oil-filled) areas, while leaving its newly-porous
    outer skin susceptible to "being disturbed even with routine,
    careful polishing of the metal around it." (Hope this makes your day
    a happier one.) And so, VOILA! Yet another case solved by Inspector
    Lappy-Dappy! 

    All my best, Doug Douglas Turet, GJ Lapidary Artist, Designer &
    Goldsmith Turet Design P.O. Box 162 Arlington, MA 02476 Tel. (617)
    325-5328 eFax (928) 222-0815 anotherbrightidea AT hotmail.com

____________________________________________________________________
T h e   O r c h i d   L i s t
Open Electronic Forum for Jewelry Manufacturing Methods and Procedures
____________________________________________________________________
Orchid FAQ:
~ http://www.ganoksin.com/orchid/faq.htm
Orchid Archives:
~ http://www.ganoksin.com/orchid/archive
Orchid Galleries:
~ http://www.ganoksin.com/orchid/gallery.htm
Invite a Friend:
~ http://www.ganoksin.com/invite.htm
____________________________________________________________________
Tips From The Jeweler's Bench - Article Archive
~ http://www.ganoksin.com/borisat/tip_sear.htm
The Jeweler's Selected Bibliography List
~ http://www.ganoksin.com/jewelry-books
Buy Orchid Jewelry:
~ http://www.ganoksin.com/shop
____________________________________________________________________
-Unsubscribe:
-Email: orchid-request AT ganoksin.com Body=unsubscribe subject=blank
____________________________________________________________________