India and Crystolon names are among the most well known sharpening stones in the world. They are made of different abrasive materials, but both are pre-filled with lubricating oil at the factory. It's a unique feature of Norton company. The oil lets you work with the stone without pre-soaking. A lubricant is required to prevent stone loading during the sharpening process. It's useful to have the oil as a component of the stone.
It's tricky to make India and Crystolon in Edge Pro format mounted on aluminum blank. The problem is oil inside the stone. It's difficult to glue something which is covered by oil. It was a long way of trials and errors before we found a glue with high oil resistance and high adhesion to dirty surface. And we did it.
Courtesy of Mr. Wizard. Please read chart explanation in README.