Squaring stone is the art of producing rectangular blocks of stone to a sufficient degree of regularity and smoothness as to be useful for building with minimal mortar, as opposed to “rough stone” work in which randomly shaped stones are either loosely piled or encased in surrounding mortar. My question is two-fold:
First, would stone masons usually produce squared stone from blocks extracted from a bed of rock, or would they sometimes “rectangularize” already loose rocks? And if the latter, then how would one measure if an irregular piece of stone had sufficient starting dimensions to be cut down to a block of a given size and shape?
The former. That way a lot of the work is done in the quarry and you have to do minimal dressing on-site. Also, the quarried stone is a more-or-less known quality, already-loose boulders are not as certain.
Can you expand on this? I’m not seeing how one might avoid thinking a stone “looks about right” only to have it turn out to not quite accommodate the diagonal corners of the squared block.
Will depend a lot on what a mason wants the intended look of a wall to be. That will be strongly influenced by aesthetics, but its also an engineered structure that has to support itself and also usually other important things like buildings and people.
If you were in Teotihuacan or elsewhere in S America and building intricate multi-sided blocks into finely jointed walls, then its easiest to sort it out at the corners and junction points. That way you get the big blocks all rectangular except where they insert a small block with about 10 sides that manages to connect to four blocks that otherwise were not going to fit together properly. Looks fantastic, and all the work is on the precision joiners, not the big blocks that look so impressive.
In other wall-building methods you shove in the odd course of adjustment stones which might look sloppy, but do the hard work of levelling the overall coursing and, critically, making sure all the loads and stresses in the wall are correctly carried off downwards.
Or, you make up the difference with layers of mortar.
Or, you say I want it exactly 3 cubits long, not 2.hand or 3.thumb or you’re not getting paid.
No, I’m not saying you just look at a stone. I mean you use measuring to see what the major dimensions are, probably do some sketches, and based on that, what the maximum useable block that sits inside that - probably with a lot of waste.
A little like all the evaluation involved here, but for a block not a sculpture:
If you measure and figure you have at least a sphere of diameter d, then you know you can get a cube of side length d\big/\sqrt{3}, for example. Or are you suggesting they would purely “eyeball” it?
Damn few rocks and boulders are even close to a sphere. Even completely disallowing any candidate stone that isn’t fully convex, that still leaves the rocks that are irregular ovoids on all three axis.
I grew up in Amherst, Ohio -the sandstone capitol of the world. There are lots of photos of stones being worked. First of all, you need the right rocks. Either sandstone or limestone is excellent for building. Granite also but I am not familiar with it. Both sandstone and limestone are sedimentary rocks made of layers of sand. They have a definite grain to them that is easy to see. They are easily quarried to have flat sides. But for that loose stone you start off by splitting the rock along a suitable grain line. This is a simple chisel job. Now flip the stone over and put the flat side down and split again at a suitable height. Now you have a irregular stone with parallel top and bottom planes. To cut this into a rectangle you need to cut across the grain and that is a job for drilled holes and feathers and wedges if the stone is large. If it isn’t too thick you can just hit a wide chisel straight down and slide it along to make a line. Repeat until it cracks. I have done a few sandstone steps and it isn’t that hard. I have also “rock faced” some stones for decorated purposes which takes a bit more skill.
Given that a bed of sedimentary stone like limestone or sandstone naturally splits into layers, and that you can more or less choose the dimensions you want to work with, what dimension ratios are typically used for building stone? ISTM that building stone is usually neither cubical nor as long and thin as bricks, but what do I know? Do you want blocks to be at least twice as long as they are thick?
You are absolutely right that there is no ordained dimensions. The sorts of considerations that go into building the stone structures I have studied and which probably affect stone dimensions and type of masonry usedare:
the natural split of the stone - yes they have layers, but how far apart are they?
engineering intent - is it a wall to carry more wall above it, or a retaining wall with pressure coming laterally from behind, decorative only, to keep out an invading army?
how is each block being lifted - if by hand of workers or convicts, then a human scale dimension would apply versus a mechanical hoist, scaffolding or a crew of stonemasons
how much lock or overlap is considered necessary - bricks work by overlapping to allow loads and stresses to be distributed - for stone having a good top surface to evenly spread that laterally and into the depth of the wall is critical to it saying upright
for freestone or shaped rocks, say in a stone field boundary wall, there are still a bunch of engineering principles about how stresses in a wall are carried, how gravity works on unmortared stone, but these can be learned as principles and then lots of practice.