There must be a lot of oil, which is produced underground and endless, unlike pine trees that will run out at a certain time. Nowadays, there are no large areas of pine forests in Shandong. Gradually, most of the mountains where pine trees grow are bald in Taihang Mountain, the junction of Henan, Shaanxi and Hubei, and the south of the Yangtze River. People who make ink probably don't understand the benefits of lampblack.
Soot is also big, often infected with black clothes. My script Yanzhou said: "Snowflakes were flying in air billow Mountain and Balang Mountain in Yichuan County, Shaanxi Province, and immediately I put up a felt tent and learned that people there lived a nomadic life. The clothes are all black, but the winter has not passed, and the oil smoke is more likely to blacken the clothes of pedestrians than the smoke of Luoyang chariots and horses. "