Answer: That depends upon what the black substance is. If it is sap, it may be just natural oozing or could indicate a wound of some kind. If it is sap that has turned black from bacterial activity, it shouldn't harm your cedar. If the black substance is powdery, it could indicate a fungal growth of some kind. Try wiping or washing it off. If you can't, I'd recommend watching the spot and the tree closely for signs of other problems.
Best wishes with your emerald cedar!
Q&A Library Searching Tips