2. The concept of rare books first appeared in Song Dynasty, which refers to high-quality printed books. Kindness means good. The original meaning of "rare books" refers to those books with good school publication, good binding, long history, small circulation and academic and historical value. Woodblock books are printed with woodcut characters. Printing was not invented before the Tang Dynasty, and characters were engraved on bamboo slips, silks, paper and sheepskin with a knife and pencil.
3. After the invention of movable type printing in Tang Dynasty, engraving printing in Song Dynasty was very developed, and the circulation of books increased greatly. Printing is divided into official engraving and folk engraving. Official engraving is handled by the court, and the quality is good. The quality of folk workshops is uneven, and there are various problems such as binding, missing words, typos, paper and handwriting. Song dynasty is the heyday of seal cutting, so there are versions of good and bad.
4. Different versions of books have different documents and different collations, so there are whole books and residual books, excellent books and inferior books; Different versions of books appear at different times in the morning and evening, and their rarity is also different, so there are differences between ancient books and modern books, and there are differences between orphans and duplicates. The connotation of rare books has also expanded than before. Later, many scholars summed up the concept of rare books, and finally formed the universal theory of "three natures" and "nine articles".
5. The age limit of rare books is now generally determined in the 60th year of Qing Qianlong (A.D. 1795).