So now I decided to examine the stresses in borosilicate marbles containing opals.
I ducked next door to the World Of Marbles and while Jo and Jan were looking the other way took a couple of the wonderful boro marbles from the shop (joking, of course). These marbles are by a great and well respected artist but I will refrain from using their name without consent.
Using the CLP lens filter I took the photos above. The stress in each of the above marbles is apparent.
Interesting...
 
 
Here is my second attempt at an opal marble. I thought I could try to put the opals in as planets in a vortex. I pushed them into the marble early in the construction and they were covered with approximately 5mm of glass by the finish.
The marble cracked badly during the making but the crack was associated with the punty, not the opals. I managed to work the crack out but unfortunately during the cooling, the opals caused some cracking.
And the third attempt. I made this on the same day; another deep-set opal. You can see that I have sorted the bubbles around the opal problem. In the third picture you can see the stress marks (photographed with a polarising CPL lens filter). Now I think I will take a look at some of the borosilicate marbles for stress...
 
 
I have been working on getting opals to survive in soft glass.
According to popular belief, opals can only be incorporated into borosilicate glass.
I obtained some Gilson opal from Profound Glass and gave it a go. I figured that a sphere deep in a sphere would stand the best chance of survival. Above is my first effort.
There are a couple of bubbles around the opal but I have since developed a technique to minimise these. I also found out that they pluck out of the glass very easily.
I'll post further pictures of opals and other experimental efforts as I get around to them