How To Encase An Opal

Seal the end of a small tube (9mm heavy wall works well)

Insert opal so that it is laying at the bottom

Heat the bottom of the tube until it is melted in and the opal is encased

Anneal at 1150 - 1225 for an hour

Leave it in the kiln to slowly cool over night - this is a crucial step

Don't open the kiln during the cool down period.