Last week’s New Yorker has a Burkhard Bilger article called “The Path of Stones” about the gem industry in Madagascar. I was skimming through it when I hit a reference to “a low-grade sapphire known as geuda” that the Thais learned to turn into genuine-looking sapphire in the ’70s. This word is not in any dictionary, as far as I can tell, so I have no idea how it’s pronounced or where it’s from. This irritates me. Once again, I turn to the assembled multitueds, with confidence in your collective experience of the world. Surely some LH reader has hung out with enough gem dealers to know how they say the word: gooda? gyooda? gee-ooda? If you know the etymology, that’s definitely a plus.


    It’s a heat treatment, this much I know.

  2. Some googling uncovered this explanation by ‘metamictman’ on a forum at
    “Geuda (goo-duh) is semitranslucent to semitransparent corundum with a milky to silky appearance in reflected light. It’s a Sinhalese word that describes milky, silky nearly worthless sapphire. It’s the type of corundum that’s best suited for heat treatment. Titanium oxide in the rutile (which causes the milky appearnce) turns blue and transparent when heated to very high temperatures. Starting in the 1960s, geuda from Sri Lanka was shipped to Thailand where it was heat-treated into gorgeous blue sapphire. Many naive Sri Lankan suppliers were told it was being used as cheap building material. Sri Lankan geuda was the basis of the Thai sapphire “boom” of the 80s and 90s.Do not confuse heat treatment of geuda with the new bulk diffusion beryllium treatment of corundum.”
    However, as I’m sure you discovered, Geuda Springs is also a town in Kansas. Most other info only deals with the treatment which turns the gem into sapphire. I hope this is a sufficient lead!

  3. Good find, KED! (And yes, I’m very annoyed with Kansas for hogging the Google results.) Unfortunately, it seems to be the only thing on the internet to even address the issue of either pronunciation or etymology; I’ll take their word for it that it’s “goo-duh” because it’s a natural English pronunciation, but I’m not so quick to accept that they’re right about it’s being Sinhalese — for one thing, the “eu” doesn’t look particularly Sinhalese (or even Indic).
    It’s a heat treatment
    Am I the only one who has a Graham Parker tune running through his head?

  4. James Crippen says

    It may be a Thai take on a Sinhalese word. Don’t know about either, but it’s possible.

  5. Presumably a sapphire is not geuda heat treated by nature. I imagine experts can tell the difference, or the bottom would have fallen out of the sapphire market.

  6. The gem market is a complete mystery to me. The article pointed out that some other stone is rarer, harder, and clearer than a diamond, but sells for much less. And why does it matter whether a sapphire is beautiful because it was treated with heat? The marketers obviously have a stake in keeping prices up, but I don’t understand why people go along with it.

  7. There was an article (in The New Yorker!) awhile back about the brandnaming of d*amonds. Apparently 100 years ago d*amonds didn’t have a mystique and were not required for engagements. A massive, decades-long promo and ad campaign coincided with deBeers gaining a monopoly on the sources.
    There’s supposed be a lot of brutality in the d*amond trade too, d*amonds from certain countries are called “blood d*amonds”.

  8. It sounds vaguely similar to gewgaw to me…

  9. MOST gems, including sapphires, have been treated in some way. In fact, the heat treatment of sapphire is one of the oldest treatments and goes back hundreds (perhaps thousands, though I’m not positive about that) of years. No one realized that geuda could go from milky white to beautiful blue, though, with heat treatment; before, it had mostly been used to take a very weakly colored sapphire and make it darker. It might also take a higher temperature to heat treat geuda, which required kiln technology that isn’t that old, but, again, I’m not positive about that.
    Oh, and, yes, an expert can indeed tell the difference between heat treated and non-heated sapphire. Something to do with a characteristic melting pattern of the rutile or some such.
    As to why a non-heated sapphire would be more than a heated one, it’s just to do with rarity. A really beautiful, cornflower blue sapphire is fairly rare in nature, thus more valuable. And d*amonds are actually one of the more common gemstones on the planet, but DeBeers has done a masterful job of marketing and controlling the supply so that prices stay high.

  10. None of my Gem and Mineral books has any hints on etymology or pronunciation. The newer ones only mention it as a source of heat-treated sapphires (with varying degrees of distain or caution) and the older ones that are otherwise full of the marvelous Victorian footnotes and digressions don’t say anything, perhaps because the process was not known or widespread then.
    As a hint to pronunciation, Japanese gem sites have ギウダ, whereas cheese sites have ゴーダ. But that could be highly dependent on the borrowing path.
    Since I was at the library, I checked out a Sinhalese-English Dictionary, an Indian reprint of one from 1899. Of course, I don’t really know what I’m looking for. With that in mind, ගොඩ ‘heap, mass; land’ is a possibility, although this user-contributed dictionary says that means ‘much’.

  11. cheese sites have ゴーダ
    Hmmm… The cheese sites I visited all have it as “gouda.”

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