Now, if the gem would stay like this forever as it is with originals that also would still be somehow acceptable, but it won’t stay like this and that’s cheating. After usually around 3 years the gem deteriorates and what is left is junk one has been bought for lots of money.
Here is how it's done
Conventional processing is to throw the stone into an “oven” as it was done already in ancient times.
Glass filled is a new treatment to pop up ugly sapphire and ruby stones; this is a newer process because it needs quite some pressure which was not available before. Usually this processing is done with African gems since they lack the basic quality Burmese gems have.