As a stone carver working in the UK I am lucky to have quite a range of local stones to choose from. That is not to say I will not work with imported materials, but my practice is generally based around using British stones. Different stones have very different properties. Some stones are close-grained and good for detailed work and others are coarser and lend themselves to bolder designs and simpler forms. Choosing the right material for the job is something that comes with experience. Some clients will come with a specific need in terms of material pallet and if this is very limited due to the setting then often the stone chooses itself and then the project is all about designing something that works in that material.
The main British stones we use are Sandstone (such as buff York stone, red St Bees stone, and grey Forest of Dean stone) Limestone (such as Kilkenny stone, Portland stone, Purbeck stone, Ancaster stone) and Slate (such as Welsh blue/grey, Westmorland Green and Caithness flag stone). There is also Granite (such as Cornish grey or Scottish red) and Marble around the UK but we don’t tend to use these much. Some limestones (such as Connemara and Purbeck) are referred to as marble, because they are a little harder and denser than other limestones, and take a polish, but they’re not true marbles as far as their Geology is concerned. I’ll not go into the geology in much depth on here, but basically limestones are sedimentary, made from calcium carbonate, and often formed in shallow seas and you can often see fossils such as crinoids and ammonites in the surface. These rocks were formed around 70-350 million years ago. Sandstone is also sedimentary, and normally made up quartz and feldspar and was formed at least 300 million years ago. Marble is metamorphosed limestone – limestone that has been subjected to heat and pressure, such as Carrara Marble which is around 200 million years old. Slate is basically compressed clay or volcanic ash formed around 400 million years ago, and this makes it much finer and less granular, although it is foliated and splits readily into layers. Granite is igneous, and formed from magma. It’s coarse grained and hard, and formed around 300 million years ago.
Sandstones vary considerably, and some are quite tight-grained (such as Woodkirk stone from Yorkshire and Forest of Dean stone) and these are good for quite detailed work, whereas Clashach stone from near Elgin, or gritstones from the Peak District are coarser and lend themselves to bolder simpler designs. Slate is much finer and perfect for really crisp detailing, which is an advantage, and it’s basically waterproof which is good for weathering, but it is also a laminated/layered material which tends to make it harder or riskier to work in three dimensions, so it’s not so suited to bold relief carvings, although it is not impossible to work it in this way. Limestones can also vary considerably, for example Cotswold stone is relatively soft and pale whereas Kilkenny stone is dark and hard. These are all considerations when designing an inscription or sculpture. For example if there is a lot of lettering needed on a small stone, then Costwold stone will not work. One might need to use a fine sandstone, or most likely I would steer you towards slate, or hard limestone such as Hopton Wood stone. Often the choice of materials is governed by the setting for the work, yet sometimes there is no obvious preference. Sometimes the material is chosen due to the brief having certain restrictions regarding size and content, sometimes the stone is the first choice and then a design is made that works with that material.
Here are a few examples of carvings in sandstone:
Here are a few examples of work in different limestones:
Here are a few slate pieces: