Greenwood Cemetery

On this stone majestically gracing the old Greenwood Cemetery in Columbia Tennessee notice how the mosses and lichens are growing in a pattern where the water streams over the stone. That is down the two sides of the middle in a band from where the pointers at the top of the stone direct the water streams during rain storms. The water enhances the growth of the plant life. The gray/white patches and splotches are known as Lichens while the yellow streaks are known to be the mosses or just different kinds of lichen. Natural patination, molds or possibly stains turn the stone from a light color to the dark gray/brown shown here. All these living plants in a way serve to protect the stone from the raw elements of nature. Upside is they protect the stone from hail and high winds and the weathering away from hard rains. Downside is they hold the moisture next to the stone in a manner so that changes in the temperature of the water or ice cause expansion and or contraction. This process may in some cases cause cracks in the structure of the stone. It is my opinion that the danger from the water retention is greater threat than the shielding effect from the elements of these plants. I am sure that does not hold true in all stones since there are a variety of stone compositions used to make monuments. It depends on the kind of stone. The very hard stones such as Granite used today in modern Cemetery memorials are not porous and therefore water poses no danger to cracking them. While I do not know the composition of the above stone it is probably limestone or even some form of sandstone. It will obviously be classified as much softer and more porous than Granite and is in danger of breaking up from the harsh elements. The softer of the stones found in Cemeteries are the limestone and sandstones. There is a great diversity in the quality of the old stones. Something else to be considered is the what is termed natural patination of the stone. This stone was light brown in color when first quarried from the earth. It has over time developed the dark gray-brown color that can be seen behind the lichens and mosses. The patination (natural color change) process is a continually changing natural occurrence which will evolve the color of the stone as it ages. I have found old flint Indian artifacts that were several thousand years old and noticed they are a different color than the ones which are only a few hundred years old. Photo and writing by Wayne Austin 7/20/2003.

Should the Lichen stay or be cleaned off.
A revised writing by Wayne Austin 8-5-05

Definition: Lichen the living woody matter that grows naturally on the face of stones including memorial stones. It may have varying lives just as other plants. some types live long lives and others are short lived.
Whether one should remove the lichen depends on how you are going to remove it. If you are going to clean the stone using a prescribed mastic then it is better to remove it but not more frequently than the prescribed
standard of every 5 years. If a person wants to remove the lichen with a chipping hammer, sandpaper or acid cleaners or other harsh chemicals then it is definitely better to leave the lichen alone. In fact never never use any of the above.
Other arguments can be made that the lichen should be left alone anyway.
I personally think the lichen's benefits outweigh the bad they cause. They do protect the stone from the eroding properties of rainwater flowing over the stone. The Lichen cushions the impact of flowing water. I think that is
the main benefit, however Lichen also cushions the impact of harsh hail and ice storms that are so hard on the stones.
The down side though is that lichen traps the water close to the stone causing any freezing to have a negative impact. This freezing water contracts the stone causing stress on the surfaces. The opposite effect occurs when in the hot
weather the heating of the stone from the hot rays of the sun causes the expansion, which also can break down the stone.
This would be offset by the cooling properties of rainwater in extremely hot weather, which yields a benefit. The ultraviolet rays of the sun also cause the stone to break down to some degree and there the lichen also protects the
stone from that. Lichen grows more on the stones in the open than the ones in the shade. If you go to a cemetery here the old limestone memorials are out in the sun in a well mowed environment the stones are in most cases more worn
and less readable than the ones that are in the shade of large trees. However the large trees may also threaten the stones by dropping debris on them. Lichen also grows more profusely in the rainy season than in droughts leaving one
with difficulty in attempting to photograph a stone right after a long wet spell. However lichen growth from the wet seasons is usually light enough to just brush off with a soft brush without harming anything. It is the hard woody kind
that grows next to the surface that is a problem to remove and may cause damage if it is not taken off properly.
It actually send roots into the pores of the stone especially highly porous stone such as limestone. If you have to remove it you will find the old growth is tough and some kinds of it will re-grow in a short period of time anyway.
by Wayne Austin 8/5/2005