Alcohol will cut the grease. Then use soap and water to LIFT out the carbon( soot,or "lampblack"). For mortises, an aggressive use of an old tooth brush may be needed to get the black out of grain, using soap and water. Give the soap time to "emulsify" ( surround, and then float out) the carbon particles. You may otherwise have to repeat this cleaning process several times to remove all the carbon.
For the most part, sanding removes more than 90% of the black. You want the outside of a stock to be 100% clean, so use the alcohol first, then the soap and water, and then sand. Since the alcohol and water often raise "whiskers" in the grain, you want to do the sanding last, so that you can remove the whiskers along with any remaining tracks of the black. :thumbsup: