Yesterday I went for a social-distancing walk at Woodland Cemetery, visited a few repairs that we did last summer (all are holding up well!), and made note of a few gravestones that have suffered some new damage. One of these stones was one that was repaired a few years earlier by another team, using one of the pinning methods that is accepted as a safe conservation technique for historic gravestones.
Historically, gravestones that had pins in them were attached together using iron, lead, or copper. The issues with the iron pins is, of course, that they can easily rust the moment moisture gets into the space, which in turn will cause the stone to crack from the inside. This damage is difficult to repair, which is why we don’t use these anymore! In place of iron, stainless steel pins have been used in more recent decades to hold broken stones together, and more recently these are being replaced with fibreglass rods. However, these materials, while they don’t rust, they have their own issues.