Q: I have seen the term “freestone” used in describing Gothic sculpture. What is freestone?
A: Freestone means stone that is uniform in all directions, that is, stone which carves uniformly in all directions, exhibits no tendency to break preferentially, and has uniform structural properties. Originally the name was used for limestones quarried in England and France. These stones’ working properties made possible the detailed sculpture and delicate traceries of Gothic cathedrals. Later the term was also applied to fine-grained, massive sandstones that had similar carving characteristics. Medieval stoneworkers skilled in working these materials became known as freestone masons, a term which many scholars believe was the basis for the name Freemasons.
Sedimentary rocks such as sandstone and limestone typically are layered or bedded, indicating slight interruptions or variations in deposition. The thickness of individual beds may be from only fractions of an inch up to many feet. Freestone is a very thick bed, indicating continuous deposition over an extended period of time for limestone, or a single episode of very rapid accumulation for sandstone. A freestone bed often has thinner beds above and below it.
The carving benefits of freestone are obvious. You don’t have to worry about directional breakage. In architectural uses (as well as sculpture) it is customary to place stone with the bedding horizontal. This minimizes water infiltration along the bedding and utilizes the stone’s strongest direction for load bearing. There are exceptions. Bedding may be placed vertically when there are strong compressional forces from the sides, such as a keystone in an arch. Using freestone simplified addressing all of these concerns, demanded less skill of the quarrier (although perhaps not of the mason), and wasted less stone.
More recently, “freestone” has been used for any uniform rock, regardless of its origin or composition. But often freestone is a matter of perception. Few stones whether igneous, sedimentary, or metamorphic are truly structureless. I have a friend who has done stone restoration work on centuries-old buildings in Europe. He has noted many instances where, after several hundred years of weathering, supposed freestone blocks now show subtle bedding, sometimes oriented to the detriment of the structure. On the other hand if I am carving what now behaves as freestone I’m not worrying that posterity and a few centuries may prove otherwise.