Article #22 - Why does a black pencil on a black slate make a white mark?

Feeling that this question deserved more consideration than was given it by the members of this association, it having been presented to them and rejected without even a verbal answer, I will bring it up again for the purpose of a further investigation. There are some questions that cannot be answered, there are others of such a nature as not to promote the object of a Lyceum, others answers to which would be uninstructive and uninteresting and to answer some would be a waste

of time. I cannot see that this belongs to either class, but on the contrary seem to be a very appropriate question and an answer to which would be satisfactory at least to the member to whom it was refered [sic]. I shall therefore attempt an answer. To be critical, it might be denyed [sic] what is implied as a fact that a pencil and slate that are entirely black does make a white

mark. But according to the meaning of the question, the reason why a mark whiter than either the pencil or slate is made, may in some degree be owing to the pencil being moist, or covered ??

substance darker than the particles left on the slate, but is owing in a greater degree to the loose condition of the particles, permitting the light to pass through them and causing it to be reflected from a greater portion of surface.

                                                            F. D.

Pocopson 2nd mo 25 1851