Paper
Paper is a thin, matted sheet of a webbed and random network of mainly cellulose fibres formed from an aqueous pulp suspension with the help of a sieve-like bamboo, textile or wire screen. The physical features of a final product are determined in the production process. The fibres of the paper typically have a very wide range of morphological properties, which can be detected during scientific examination depending upon the type of raw materials used and where those materials came from.
Usually, long fibres are better than short ones for papermaking, but more difficult in processing. The long, thin fibres interlace each other better and the paper has better tensile strength. A longer fibre means a higher degree of polymerization of cellulose, also corresponding to a higher molecular weight. For this reason, when the size and the thickness of the paper are the same, rag paper is heavier, bark paper is lighter, and bamboo paper is the lightest. On the other hand, short fibres like cereal straws or grasses allow for making softer paper characterised by higher absorbency, which may be better for printing. However, such paper has much lower tensile strength (Ferdous 2021).
Beyond the raw materials, there are other aspects of the papermaking process which influence the nature of the resultant paper, such as the degree of fibre blending, the type of papermaking mould used, and the preparation of the paper surface before writing or printing upon it. Such technological elements are often typical of the time and area of influence of a certain culture.
Another parameter for paper description is the assessment of flocculation: that is an uneven distribution of fibres when looking at the paper in transmitted light caused by the tendency of long and slender fibres to form relatively dense assemblies, or ‘flocs’, in water suspension (Kerekes 1995).
The assessment of paper quality is particularly difficult as it combines objective parameters, such as the examination of the raw materials and the technologies used, to subjective ones, like the aesthetics and the purpose the paper had in a particular historically defined period of time. We must therefore bear in mind that the description of paper quality is not universal, and might not always correspond to general standards of paper quality elsewhere.
If the basic concept of paper and papermaking remained stable, the materials and technologies employed changed drastically depending on geographic areas, periods of time and cultural milieus, allowing for establishing its provenience and date. These technological differences regard mainly the raw materials employed (new plant fibres or recycled textiles), the types of moulds and screens used to collect the pulp and form the sheets (floating vs dipping mould or flexible vs rigid/laid mould), the various additives, glues, fillers and coatings added during the sheet formation and the finishing phase (formation aids, starch glues vs gelatine, kaolin and rosin, etc.).
History of the material:
China and Central Asia are the place of origin of paper, and the technology of papermaking has been manifested in high skills and large variety of materials used. The invention of paper is traditionally attributed to Cai Lun (an official at the court of the Eastern Han dynasty) during the course of the 2nd c. CE in China, although it is more likely that he only improved an already-known process. In fact some studies place the invention of paper to the 2nd c. BCE in West Han, since small fragments of what appears to be paper have been discovered in archaeological excavations (Pan 2011). The controversy essentially rests in the difficulty to determine whether they are indeed made of paper or of paper-like material, since the difference between these two types of writing surfaces is mainly technological and difficult to identify in small fragments.
From China and Central Asia papermaking spread to other parts of Asia along trade routes, during the 4th and 7th c. CE, likely thanks to the involvement of Soghdians and Buddhist monks. Arabs entered into contact with paper during the course of the 7th and 8th c. CE, and in the following centuries contributed to the development and adaptation of papermaking techniques to different contexts of production and use, and to the spreading of both the material and technique towards the West and in the Mediterranean region, up to al-Andalus (Bloom 2001; Bloom 2017). The beginning of Western papermaking can be set to 13th c. CE, when the techniques likely learned in Palestine and Syria during the Crusades, were further developed in Fabriano, Italy, and spread rapidly through Europe. The cheaper price and the higher volume of sheets resulting from these innovations contributed to the success of this product at the expense of other writing materials and determined the decline of Arabic papermaking in the Mediterranean and African regions. Western papermaking continued to evolve through the elaboration of techniques and equipment that would fasten the process, culminating during the Industrial Revolution with the invention of the paper machine (in 1798 by N. L. Rober) and the introduction of new raw materials thanks to the development of chemical beaching and sizing (chemical bleaching of mechanically extracted wood pulp 1802; alum-rosin sizing in 1807), and chemical extraction of wood pulp in 1851 (Hunter 1978).
Relevant analytic methods include:
- Optical microscopy (Helman-Ważny and Van Schaik 2012)
- FTIR for fibre identification (Espejo Arias et al. 2011), and for the identification of sizing agents and fillers (Kropf and Baker 2013)
- XRF for the identification of fillers and other additives (Manso 2008)