|Synthetic corundum is made through a variety of processes today, but two create the majority (by weight) of synthetic corundum on the market today. The Vernueuil process and the Czochralski process.
For more complete explanations of these two process see these additional pages. There are step by step diagrams and an animation of each.
The stone was cut from a split boule of red colored corundum (not ruby). The color is called "garnet". Corundum boules created in the Vernueuil process often have very high internal stress unless they are very precisely temperature controlled. To relieve the stress the boules are split and usually sold in this manner. Both boules were grown by the Verneuil process.
Below are two split boules, notice the outsides show a rough texture directly form the growth environment, and the centers (in the split view) show glassy clear interiors.