Went back to drilling again this afternoon, I had a 5/8 diamond core that I planned on using on the back side as a counter bore. This time I had no problems drilling, but got some ugly blowout on the bottom side, more than I would have thought. So maybe drilling 1/4" holes through 2" of granite is not a good idea. The plate I am drilling is not what I intend on using for the lathe, but it has given a bit of practice. I did find a surface plate on ebay today, and when I bought it I thought it was granite, I may be wrong.
I am thinking this may be a ceramic surface plate. If it is ceramic, would it make a good lathe base? Can you drill ceramic?