If you’re like me and just naturally curious, and combine that with writing, you’ll find that it leads you down curiouser and curiouser paths. Today it led me down the path to find the difference between pitch and tar, which came from the search for the etymology of the idiom “toe the line”. So what is the difference between the two? Quite a bit and not a lot, it turns out.
Pitch is a general term for either natural resins or manufactured derivations. When it comes from plants it’s known as resin (and products made from this, such as violin string conditioner, are called rosin), and has a surprisingly wide range of applications, from waterproofing ships, Norse Longhouses and Stave churches to use as a glazing agent in medicines and chewing gum. The confusing thing is that some forms of pitch can be called tar. Bitumen is a natural asphalt, also known as “oil sand” (an irregular petroleum deposit), which is a type of pitch. Pitch is a natural viscoelastic polymer, which basically means that even though it seems hard and may shatter on a hard impact, it is actually a liquid. The Pitch Drop Experiment was started in 1927; since then, only 9 drops have fallen from the funnel filled with pitch. That’s patience. They were able to determine that the viscosity of pitch is roughly 230 billion times that of water. Just thought you should know.
Tar is obtained through a process called “destructive distillation”, along with other products such as coal gas, coal tar, coal oil, gas carbon, Buckministerfullerene, coke, and ammonia liquor. Its connection with pitch is that it can also be derived from pine. I’ve seen puddles of natural tar all over the Highlands of Scotland, as the pressure of weight from the dense peat moors presses the tar out, much like a sponge being squeezed. It can make hiking through the wilds of Scotland a messy business. In fact, in Northern Europe the word tar refers to the substance obtained from pine wood and roots. The distinction between pitch and tar is that the former is denser, more solid, while tar is more of a liquid form. So, it seems, that’s all the difference between the two terms comes down to: Viscosity.
And that brings me full circle in understanding the idiom to “toe the line”: The “line” was the strip of weather-proofing between a ship’s deck boards; this was made by packing a mixture of natural debris (sawdust, straw, etc.), pitch and tar between the boards. It would be therefore logical to assume that tar and pitch were mixed together to make it both spreadable and solid.