Ok! So, at my class in October I cut an Ethiopian opal (actually I cut 2) that has changed a lot over time. We learned that Ethiopian opals in particular have water content issues called 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. Sometimes this highlights the color play – others will just become transparent or opaque, with no color when hydrated.
One of the stones was clear when I received it, and if you put it in water and looked very closely you would see a red flash. In the months (it seriously took over a month) since class it has turned a milky white color with a pretty red flash that is prominent. I have explained the change to people when they see the stone, but I don't think they fully understand the dramatic nature of it. And hey, I get it, they weren't there. But look at this!!
I bought a mixed lot of Ethiopian opal online and recently it arrived to me. It was sold to me by weight, and the largest piece was an (ugly) lumpy no color thing. :/ That's ok, it happens, and that is the risk you take buying things this way. Also, there are a lot of lovely (smaller) pieces too.
Do you see the large lumpy piece and the milky blue piece I circled?
Today I was looking at them and thinking again about the ugly lumpy one, and thinking that it was 'potch' (unprecious material found around opal, or basically opal but without any color play) Usually potch is something you grind off of a stone and don't want. So, it's particularly annoying to have a giant piece of it in a lot sold by weight. Oh well.
And then I thought, 'I wonder if it will change in water.' So I took it and the milky blue one and put them in water. After a few minutes I looked at them:
Look at the how the water is absorbing into the stone!! Changing it to transparent! And here it is a few hours later:
Notice that the milky blue is now a transparent green.
Our friend Lumpy:
and our friend Milky Blue:
And well, even though Lumpy went transparent for me, still no play of color, making it an ugly piece I'm unlikely to cut, BUT, I am excited to have visuals to share showing the changes that happen with hydrophane material!!