Re shaving cream.....THE SHAVING CREAM HAS ACID IN IT, and it is not a good idea. Esp. is you don't have provision to wash it off after. Yes, you do get good pictures from it, but since the stone is already deteriorating, it will just help it along at a greater pace. I guess it is up to you.....It will be gone for future generations if shaving cream is used...... Not trying to be an alarmist. I have a Masters Degree in Historic Preservation, and this is what we learned in school.....Some folks use flour, sort of dusting it on, then washing it off after.....This is not always an easy answer. Wilayne in Michigan