1 Answer

You should not use oil. Its best to use water. Oil heats up. Diamond bits are best for most stones, and you always want to take it really slow.  Water stays cooler and if you have a constant trickle things will go faster. You dont want your stone to get hot because all stones have natural lines that will crack or break. Using oil only helps heat up the stone and keep it warm. 

Cool water and a slow hand and even more patience. Never push your bit /blade for more than a second or two. Its time consuming but will save you from the heart break of ruining a stone . If you are grinding you can go longer  but still don't allow the stone to get hot, and still keep the flow of water.