Soap is usually used to refer to black. This meaning comes from the use of ancient dyeing technology. In ancient times, when making dyes, people usually used plant or animal materials to extract pigments, among which black dyes were made by grinding some special plant or animal materials into powder and adding water to stir. The color obtained by this black dye is very dark, similar to modern black.

At the same time, the word soap also has an extended meaning, indicating a dark, gloomy, negative or evil image. This meaning is mainly because black is associated with dark and uncertain things in people's cognition.

Therefore, in some idioms and idioms, such as the use of indistinguishable, life and death, it means that the result or truth of the matter is unclear, or that the matter involves dark and indistinguishable factors.

Historical sources of words:

The historical origin of soap characters can be traced back to the evolution and formation of ancient Chinese characters. According to the research, the shape of the early soap character is different from that of the present, and it is composed of two parts: the water character symbolizing spring water above and the black ink character symbolizing black below. This glyph combination symbolizes black spring water, which was used in ancient times to refer to black dyed by thorns.

In the later evolution process, this glyph was gradually simplified into a modern soap character, retaining the meaning of black. According to historical records, this word first appeared in the book Reading Records to refer to the black first frost season. With the changes of the times, people's use of soap characters has gradually expanded.

It is not only used to describe colors, but also used to express dark, gloomy and negative images. The use of this extended meaning is mainly based on the connection between black and dark and uncertain things. Therefore, the word history of soap character can be traced back to the formation and evolution of ancient Chinese characters, and its meaning and usage gradually enriched and expanded with the passage of time.