Asphalt, or better, bitumen, was found in ancient times in pools or on the surface of water, having seeped up from the formations below. It was a natural resource, collected or mined for use and export. And every source was distinct in its properties although for the most part the chemical composition was the same. The difference between hard asphalt on one hand and oil which would pour on the other, is due to the amount of entrained volatile gases.
The use of asphalt is so ancient that its beginnings are lost. The oldest attested use is possibly on a reservoir at Mohenjo-Daro in India, dating to the third millenium BCE. The material was called earth-butter by these early Buddhist builders. And parts of the Bible also dating to this period, mentions pitch, or bitumen several times. The original Hebrew words are translated according to the perceived intent as to meaning. Pitch for boat-building and slime for waterproofing basketry.
When oil seeps out to the surface, th e entrained gases slowly escape, making the asphalt left behind more viscous [thicker ]. Some oil reaches the surface already thick, while other sources are quite thin a nd fluid. Oil in pools tends to be thicker than oil found on the surface of water. Many, many variables determine the thickness of the asphalt, and many are unde r our direct control. Mixing asphalt with clay or aggregate makes it much thicker. And heating will drive off the volatiles quicker while making the asphalt more fluid, temporarily.
Pitch, slime, bitumen, all are variations of the same resource, but vary according to the use. And the use depends upon the asphalt's viscosity. Slime, being very fluid, would be ‘painted’ on a surface fo r waterproofing, while pitch, thicker, would be stuffed into cracks to stop leaks. The whole point here is that there is no real definition of the var ious terms used when talking about asphalt. The Bible mentions pitch and slime in the same sentence implying two different substances where what is really meant is two different uses.
There are several large lakes of natural asphalt which over time have hardened into a false-appearing surface. Animal s ventured out on these lakes, then have broken through the surface to become tr apped and entrained. This is today a bone-pit from where the paleontologists extract and reconstruct animals long since extinct. The asphalt in these lakes have as much as 35% entrained clay and other impurities.
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