Opal is a hydrated amorphous form of silica (SiO2·nH2O) which its water content may range from 3 to 21% by weight, most of the opal from Wollo, Ethiopia, is hydrophane. The term hydrophane comes from the Greek words meaning “water-loving” and describes their ability to absorb water and change from opaque or semi-translucent to translucent or transparent.
Four different colour Ethiopian hydrophane opals, (A1) 6.243 cts, (A2) 6.123 cts, (A3) 8.719 cts, (A4) 9.353 cts, were used to measure and monitor the physical appearance changes under wet (put under water) and dry condition.
These four opals were submerged in water with the water temperature of 27ºc, and each picture were taken at 10 minute intervals to record the visual changes.
Transparency of these four Ethiopian opals start showing changes on the first 10 mins. Opal A1 took 30 mins to improve transparency. Opal A2 around 40 mins, where A3 and A4 only took 20 mins to show the improvement of transparency.
Gas bubbles can be seen forming under the A1 and A2 from 20 mins onward, and getting more on A2 after 40 mins.
Play-of-colour of opal A4 show slightly improve of colour patches after 20 mins in water. Opal A1, A2, and A3 have no obvious improvement in play-of-colour after submerge in water for 80 mins.
The weight of all these four opals were measured within a minute after removing from water. Weight taken on (A1) 6.474 cts, (A2) 6.444 cts, (A3) 8.793 cts, (A4) 9.473 cts. Minor percentage of weight changes can be seen on these four opals that submerged in water for more than an hour. Base on the result, opal A1 has increased 4% from the original weight, A2 with 5% increased, and A3 and A4 with 1% weight increased.
These four opal were then placed in a closed room environment with room temperature of 26-29ºc with humidity of 49-53%. Each of the following pictures were taken with 2 hours intervals.
Transparency of these four opals revert back to the initial stage after 6 hours.
Weight taken after 8 hours with (A1) 6.243 cts, (A2) 6.123 cts, (A3) 8.719 cts, (A4) 9.353 cts. All these four opals have no different in weight from the original before placing in the water.
The result of this test shown that the Ethiopia opal can change transparency after placing in water for several minutes. Besides, this test also shown that not all Ethiopian opals will improve play-of-colour after submerge in water for hours, and not all Ethiopian opals will absorb water for more than 5% of it’s body weight. The effect is not permanent, all these four Ethiopian opals in fact revert back to its original state after placing it in a closed room environment for 8 hours.
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