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A Large Andamooka Sugar Treated Matrix Opal

In Fine Jewelry > Opal Jewelry > Show & Tell and Gemstones > Opals > Show & Tell.
Opals7 of 10An 11ct South Australian Opal "rub" from Coober Pedy, circa 1930's Australian Crystal Opal Semi Black/Black  7..41ctw
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    Posted 5 years ago

    (114 items)

    The pendant shown above is set with an Andamooka Sugar Treated Matrix Opal. This is interesting variety of treated opal from South Australia. It's a porous sandstone base (or matrix) which is shot through with fine grains of opal that fill the pores in the sandstone matrix.

    This opal is 29 x 17 x 8mm, giving an estimated weight of around 20cts, making it a very impressive pendant.

    When Andamooka matrix is mined it's a pale rock with very little show of colour, however it's then chemically treated to blacken the sandstone, which provides the dark base to show off the opal within.

    The matrix is soaked in a saturated sugar solution and then cooked in sulphuric acid. This carbonates the sugar soaked up within the sandstone, turning it black. The process is permanent, and the stone maintains its colour forever.

    Andamooka matrix can be spectacular, however it is NOT black opal, neither is it precious gem opal.

    The sugar treatment process was discovered in the 1950's and for a time it was a popular way to produce attractive jewellery for the local and tourist markets. Very little is produced today, and any pieces you come across now, like the one above, are probably made in the second half of the C20th.

    It's quite easy to distinguish matrix from gem opal, which has a smooth glassy surface if you look at it through a loupe, whereas matrix is a finely grained rock with minute pores.

    You can just see this graininess in the pics above if you enlarge them and look at the places where the light is reflecting off the stone.

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    1. vetraio50 vetraio50, 5 years ago
      Thanks for explaining the 'treatment'.
      Can you tell the difference from photos ?
    2. kiwipaul kiwipaul, 5 years ago
      Hi Vetraio, just added some more info at the bottom of the post, hopefully you'll be able to see the graininess in the pics where the light is reflecting.
    3. blunderbuss2 blunderbuss2, 5 years ago
      Thanks for the lesson, as I still try to learn something new everyday.
    4. valentino97 valentino97, 5 years ago
      I like it and love it! My birthstone is opal so I have opal preference. My favorite opals are the blues, rosy, tan and light blue tones. I love green - my favorite color - but I don't love the dark green opals. Sorry.
    5. kyratango kyratango, 5 years ago
      I'll have to buy one to see in real the difference, thank you for posting it!
      It is stunning that the cooking in sulfuric acid doesn't dissolve the stone Ô..ô !
    6. MeliG MeliG, 5 years ago
      Mexican fire opals and yours are the two favorites on mine of all the different types. The color on yours are just brilliant, very pretty! Thanks for the share :)
    7. davyd286, 5 years ago
      I wonder if you could tell me anything about my opal pendant posted here:
      Thanks in advance
    8. AnneLanders AnneLanders, 5 years ago
      thank youso much kiwipaul...yes I have an ebay search up. trouble is, its so hard to know if some of her work is being listed, I might reinstate my opal one...oh no, those darn Chinese know the POWERHOUSE really well as they have John Slaters private collection of his lifetime collection of Slater patent....gosh I wish they would re exhibit, I'll have to come up with a reason....

      thank you again, and any pieces you'd like to show as museum pieces at my place, just let me know :)
    9. kerry10456 kerry10456, 5 years ago
      Again...OUTSTANDING piece you've shared, love all your rocks. I believe this to be my favorite thus far !!!
    10. ozmarty ozmarty, 5 years ago
      Beautiful and thank you for the knowledge I did not know about this tipe of opal / treatment ..

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