How to check if an egg is fertilized?

Hey, i found an egg very near to a pheasant roaming field so i am pretty sure it is pheasant egg as its blue and quite small. I have placed it in a cardboard box filled with straw and put tin foil around the sides to keep in the heat and added a wet sponge for moisture and a light bulb. Although, i don't know if its fertile. Many people suggest candling? This doesn't seem to work as the egg has a dark, bluish greenish thick shell and i can't see inside it? Help?