Investment casting is process where parts are produced inside a mold (a.k.a., investment) which is then removed from the part to expose the molded piece. As the investment casting process typically requires high temperatures to liquefy and pour the metal alloy into the mold, discoloration of the final part is common. In addition, the investment material can often get stuck inside slots and grooves of the part. Both the discoloration and stuck investment can be seen in the part on the bottom of the picture.
The clean part seen in the top of the picture was a result of abrasive blasting. In this case, the hard metal alloy part was tumble blasted with White Aluminum Oxide for only a few minutes. The end result is a clean, uniform surface finish ready for the next steps in the part production process.
A good explanation of the investment casting process can be found on Wikipedia at http://en.wikipedia.org/wiki/Investment_casting.