Memorial headstones and gravestones that are exposed to the elements (as virtually all of them are) will eventually begin to show signs of weathering and erosion from wind and rain. They may have begun to show discolouration as moss and mould takes root on them, or nearby trees shed their leaves over them. This process can be slowed a lot with the correct memorial care such as removing anything that attaches to the surface of the stone quickly and not picking a plot that is sheltered from the worst of the weather.
Eventually, however, all gravestones and memorials will begin to show signs of their age, which is when the time comes to perform a full renovation. Due to modern techniques and the expert care that is available during renovations, a gravestone can end up looking as good as new with an infinitesimally small loss of material or structure.
Discolouration can be treated by the smallest layer of the surface being removed and the underlying stone being re-polished. The tools that are used allow the finest of details to be maintained on memorials, so inscriptions, carvings and motifs can all remain in place. Any lettering that has faded over time is easy to replace as well, regardless of whether it is inscribed, painted, embossed or a variety of other techniques.
Memorial care packages may well cost less than you think too, and the cost is further reduced by doing easy, basic and quick checks on the gravestones you which to maintain yourself.