Respecting and Enjoying a Cemetery
Gravestone Rubbing is described at ancestry.com. We want to emphasize the precautions about checking that the stone is sturdy and that any cleaners or tools won't do damage. These two photos, a well done rubbing showing the beauty of the art and the other showing its age and, according to the source (a blog), maybe damage from repeated rubbing.
There are websites that mention flour to bring out the text, BUT many, more authoritative sites that say don't. The flour residue on the stone can hold moisture, feed microbes, etc. The website, http://www.gravestonestudies.org/preservation.htm, covers the subject in more detail.
As an alternative, use aluminum foil. "...one begins by simply placing a thin sheet of aluminum foil against the stone, or wrapping it around the stone. The cheaper and thinner foil works best for this method, as the heavier name brand varieties can be too thick to work with. Then with a lightweight brush, such as a clean makeup brush, you gently press the foil into the carvings of the stone. Remember, if securing the foil with tape, only tape foil to foil, never put tape on the actual stone." The stone (left) is unreadable (computer editing seemed to be no help) but the foil (right) is readable.
The internet also covers photography in a cemetery. Ancestry.com. The author has many helpful hints: knee pads for that low shot; clippers to trim around a headstone, and so on. Again, the admonition to use care and to respect the fragility of the markers is emphasized.
If you are or become seriously interested in studying cemetery memorials, art, preservation---whatever, you can start on the internet.
One web source in the University of Massachusetts, Amherst, W. E. E. DuBois Library. Their collection includes online books on the subject. For example, Markers (1980), available in a variety of formats: pdf, kindle, text, djvu, etc.
The Association for Gravestone Studies (AGS) provides links to their archives, external links, and preservation.