Some of the opals from Mexico exhibit
a beautiful play-of-color effect,
showing patches of red, orange, yellow,
and green when polished as cabochons.
Those with a bluish body color are
called "water opal," and
orange-colored ones are referred to
as "fire opal." The Aztecs,
whose civilization flourished in modern-day
Mexico from the mid-14th century until
1520, used opals in their jewelry.
Development of the Mexican opal mines
was renewed in about 1850.
Mexican opal's beauty lies in how
the brilliant patterns of colors seen
in these highly transparent gems change
with the viewing angle. In water opal,
it appears as if the flashes are trapped
in clear water; in fire opal, they
appear to be trapped within a flame.
The patches of color generally become
weaker in more transparent stones,
and high-quality pieces are rare gems
that manage to combine these opposing
Around 1960, there was a surge in
the popularity of Mexican opals, and
Japanese consumers were especially
fond of them. At the time, its popularity
in Japan was said to be surpassed
only by that of diamond, ruby, and
Mexican opal's marketability suffered
after 1970 because of repeated cases
where cracks developed due to a loss
of water content. Details varied widely,
with some stones developing cracks
immediately after being polished,
others after a few years of use, and
so on. These days, rings set with
Mexican opals are often brought in
for remodeling or remaking, a fact
that attests to the popularity once
enjoyed by these gemstones.
Newly polished Mexican opals are reappearing
in the marketplace, though on a small
scale. The opal miners know which
exact spots produce the best material,
and rough stone prices reflect this.
Cutters who are concerned with their
reputations buy rough material that
they know will not develop cracks,
and polish them only after confirming
their quality over a period of three
to four years. This is another example
of how "who you buy from"
is more important than "what
you buy" when it comes to gemstones.
It is important to wear Mexican opals
to give them natural moisture. When
cleaning opal jewelry, it is best
to use a soft brush with mild soap,
avoiding ultrasonic cleaners.