Actually, I’m forgetting one instance in which allowing a liquid to freeze produces a reliably flat surface. I recall reading a very long time ago that the key advance that made movable type really practical was development of an alloy that did not shrink or expand when it cooled from liquid to solid, allowing a “true” type face to be cast easily. Sorry, no cite at hand.
I hope that was a whoosh. :dubious:
The surface freezes around the edge - the unfrozen middle heaves through expansion - as the freezing extends inward, the heaving becomes more pronounced, until the zone that is freezing is actually forming the walls of a rising tube.
There used to be controversy over this, but I believe the above has now been confirmed by observation.
I’ve read that the ancient Egyptians leveled the sites of the great pyramids by building a dike around the site, flooding it with water, drilling reference holes to identical depths from the water’s surface, and then flattening out the site to the bottoms of the holes. Opposite corners of the pyramids are level to within an inch or so.
Straight edges are actually pretty easy to make, all it takes is a good hand and plenty of patience. A skilled draftsman or artist can make a reasonably straight line with no tools at all, other than a writing instrument.
In the case of a spear, the shaft most likely would have been made from a sapling tree which was reasonably straight to begin with, then the irregularities would have been removed by sand rubbed by hand (most likely protecting the hand with leather) while the shaft is turned by hand. One technique not mentioned, that most likely would have been used at some point, is the use of paint. You put paint on a surface, let the paint dry, and then lightly rub the surface with an abrasive, and high spots will show up as paint free areas, apply more paint, rub again, check for high spots and continue until it’s level.
Hand polishing (or lapping) can be surprizingly accurate. In shop class, I made a rather complicated (and large) vise, and after heat treating, I needed to get the surface of the fixed jaw as flat as possible. I tried everything to get it flat, from using the school’s wire-EDM machine, to the surface grinders, and every time wound up with less than desirable results. Finally, I took a lapping stone and began polishing it by hand. Many, many, many, many hours later, it was flat to within .0001 of an inch across it’s entire surface. To give you an idea of how this compares with what I have to deal with in industry, most things have to be flat to within .001 - .005 of an inch.
>I recall reading a very long time ago that the key advance that made movable type really practical was development of an alloy that did not shrink or expand when it cooled from liquid to solid…
There are various casting alloys that differ slightly in how their volume changes during freezing. Some of these work at very low temperatures, even high room temperatures. Many of them have indium and tin and bismuth and similar metals, and they are sometimes eutectic (alloyed in a ratio that minimizes the melt temperature). You choose these partly on the basis of exactly how much growth or shrinkage your application wants.
I think freezing water is unusual because it would like to freeze from the top down, and depending on how the edges are treated you can get a flat frozen piece because of this.
Spears and especially arrows were also straightened by heating and bending - sighting along them and rotating to spot the ‘wiggle’ - then bending carefully in the right spot either by hand, or across a notched stone, or using a tool that looks like a ring on the end of a stick.
Just so you know, this is how they started making cheap window glass back in the 50’s, called Float glass - pouring molten glass on molten tin. Before that, window glass involved rollers and polishing, but float glass got you very flat surfaces for free.
True, but that won’t get out the lumps caused by knots.
That’s right - for something as big as a spear, they’d be sanded or shaved off - for arrows, it’s a bit easier to find straight lengths of sapling that are not significantly knotty.
Either way, a combination of techniques would probably be used to achieve a good straight shaft.
And, just for the sake of dotting the "t"s and whatnot, two other methods of producing plate glass were: blow a large cylinder then cut and unroll it, or blow a sphere, open the end, and spin it out into a disk. The latter type was called “crown glass” because of the characteristic “crown” deformity in the center. Or so I’ve heard.
It should be noted that, even in flat, Newtonian space, a laser beam still isn’t necessarily a straight line. The path of any individual photon is, but the beam is made up of many photons. If I stick a laser pointer on a turntable, the beam will have a spiral shape.
Thank you for posting that link. I had no idea what Mesquite-oh and Derleth were talking about until I read that.