With my Moderator hat on I have changed the heading of the thread ...
... but I think a better, and larger, image of the mark will be needed (Images can be, say, up to 800 pixels width, as long as the Kb size is 125 or lower). Also, it might be an idea to try some background paper against the inner side of the bowl to make the mark stand out. Or, if it works on this particular mark, dust it lightly with talcum powder then gently wipe off the surface powder to leave the mark highlighted in white.)