One day, he saw the remnants of Li Si's seal script, and after carefully studying the brushwork of Li Si's seal script, he was deeply moved and amazed. To this end, he wrote a special "On Pen". Cao admired and studied Li Si's seal script, but he did not copy it, but had his own innovation and development. His seal script is somewhat different from Li Si's. The most obvious feature is that he used the techniques of "hanging needles" and "hanging dew" when writing those long vertical paintings.
The method of "hanging needle" means that when the seal script is painted vertically, the strokes are clumsy, the lower end is sharp, the strokes are like hanging needle, and the brushwork is vigorous; "Dew hanging" means that when writing a vertical picture of seal script, the pen is slightly raised to the left of the pen collection place, and then returned to the front to collect the pen, showing a round pen shape, such as dew, which is very graceful.
His two brushstrokes also have different uses: when writing the first chapter of the Five Classics, he used the "hanging needle" method; When writing the emperor's chapter table, decorate it with the method of "hanging dew" Hanging needles and hanging dew, as long as people imagine this gesture of calligraphy art, they will feel lifelike and wonderful. Unfortunately, Cao's book has not been handed down.
Nowadays, people who are interested in calligraphy almost know how to hang needles and pens, but many people don't know that it was created by Cao in the Eastern Han Dynasty. Of course, his creation is not groundless. On the one hand, he is proficient in ancient Chinese characters, which should be inspired by the ancient Chinese characters of the Warring States and the sword-coin characters in the new period; On the other hand, he may be inspired by things in life or nature, so he has such wonderful creative inspiration. It is on this basis that he reformed the brushwork of Li Si's seal script and created the technique of hanging needles and exposing the dew.
Unexpectedly, a small change in calligraphy techniques will eventually lead to a change in the style of seal script. After the hanging needle and hanging dew brushwork became popular all over the world, it evolved into a unique style of hanging needle and hanging dew.