Canvas, as a material for painting, was first used by the Venetian school of painters in the 16th century and later spread throughout Europe and the world. Today, not only oil paintings mostly use canvas as a base, but also many watercolors, acrylic paintings, and some mixed media paintings are done on canvas. Prior to the 16th century, altar paintings and panel paintings in Europe were mostly made of cloth or linen and were glued to thick wooden boards, unlike later paintings that were mainly stretched on wooden frames. In the study of painting materials, these glued cloth wooden boards and metal boards, marble boards and other materials are collectively referred to as hard bottoms, while the canvas stretched on a wooden frame using fiber materials is called a soft bottom. Nowadays, the heavy and spliced wooden boards with glued cloth are rarely used, but some people still choose thinner plywood or cardboard to paint exercises and small works, and sometimes continue to use the method of gluing cloth on top. However, most painters, whether creating large-scale works or small exercises, mostly choose canvas because of its advantages such as easy mobility, convenient exhibition and collection.

Canvas consists of two parts: the textile material used as a support material and the coating layer applied on it. Both are closely related to whether they are suitable for painting operations and the stability and life of the finished works.

Currently, several types of textile materials are suitable for making canvases, including hemp, cotton, and synthetic fibers. There are many varieties of hemp such as flax, hemp, ramie, and jute. Venice was the largest seaport in Europe at that time, and flax was mainly used to make sails for ships. After long-term exposure to light, wind, and seawater erosion, it proved to be more durable than other hemp fabrics such as cotton and jute. Therefore, Venetian painters also used it as their first choice for making canvas. It is said that Tintoretto and others also used ramie canvas to paint large-scale paintings because theoretically ramie fibers are the longest. Ramie is also grown in the Jiangnan region of China, but most of the finished products I have seen are not strong enough. Heilongjiang Province is the largest producer of flax cloth in China, and many Chinese painters choose flax cloth. However, the highest quality flax cloth in the world is woven from rain-fed flax produced in Belgium and Germany, and its fibers are gray. Tightly woven cotton cloth is also suitable for medium-sized paintings. China is a large cotton-producing country with many varieties of cotton fabrics to choose from. Generally, plain weave fabrics with a warp and weft density of about 80x30 and using 12-16 yarns are used. Fabrics with too many holes or too many knots cannot be used, and fabrics that are too thick and dense like rainproof canvas are not good because the coating is not easy to penetrate.

There are many types of synthetic fibers, and the main ones that can be used as canvases are some blends of chemical fibers and cotton. However, the selection must be very cautious. Hemp, cotton, and synthetic fibers are easy to identify. Hemp thread breaks smoothly when pulled by hand, while cotton thread breaks with bending and branching at the end. Synthetic fibers curl up when burned with a lighter and have a plastic smell. Rough fabrics with a large number of knots of short fibers, such as jute cloth used only for weaving jute bags or regenerated fabrics made of hemp scraps and cotton scraps, cannot be used. A simple method to test the strength of fibers is that the thread end is not easy to break by hand.

In addition, regardless of whether it is hemp, cotton, or synthetic fibers, there are also great differences in weaving technology. Making canvas generally uses a single fiber woven into a relatively uniform plain weave fabric. Diagonal or herringbone weave fabrics are not suitable. Blended fabrics need to be carefully identified for their weaving methods and quality. Elastic synthetic fabrics with large differences in warp and weft fibers, especially interwoven fabrics made of different fibers cannot be used because different fibers will shrink differently in humid air changes and can easily damage the picture. As for whether to choose coarse or fine stripes, it depends on the painter''s style and preferences because canvas stripes can become a kind of language expression in oil painting. Some people want to make full use of it, while others do not want it to appear, just like some people choose glossy paper for printing photos while others choose paper with a texture.

Regardless of whether it is a hard bottom or a soft bottom support material, it must first be coated with a layer of coating that can ensure the stability of the base and is suitable for painting on it before painting can be done. This necessary coating is called "gesso" in Western painting techniques and has three types of preparation methods: pure gelatinous gesso, oily gesso, and semi-oily semi-gelatinous or tempera gesso. Today''s canvas coating produced by Western painting material manufacturers is collectively called Gesso. Chinese manufacturers have also produced imitation canvas bottom materials or glue for canvas bottoms but there is no unified name for them yet. Fortunately, those who paint oil paintings know its purpose but may not always be clear about its composition and characteristics. In fact, the term "Gesso" comes from ancient Italian and used to specifically refer to pure gelatinous gesso made by mixing animal glue with amorphous gypsum (plaster), which was favored by southern European painters during the Renaissance period. Northern painters living in Flanders, Holland, and Germany at that time were accustomed to using natural calcium carbonate (European painting industry called Spanish white; commonly known as talcum powder in China) mixed with animal glue as a coating material. Before oil painting appeared, it served as a tempera painting service on panels or walls. Later it became a bottom preparation material for oil painting and some modern gouache paintings. Of course, there was also a popular deep brown coating made from burnt sienna glue made by iron oxide red until Goya still used it in the 19th century. These kinds of gelatinous coatings have formed commonly used gelatinous formulas by the 17th century through years of experience using them. That is to add two parts of coating powder to one part of thick glue by volume plus one part of water mixture. Today''s commercial Gesso still roughly follows this gelatinous formula. Only traditional animal skin glue has been replaced by synthetic ethylene and propylene-based adhesives.

The original method of oily gesso was just to thinly coat an oily layer made of linseed oil mixed with zinc white or titanium white (lead white was used in ancient times) on a finished gelatinous gesso layer. This method was popular during the Baroque period of Rubens and Van Dyck. A few years ago when French painter Yves Klein came to China to teach he taught this method as well. However, in the 19th century some people advocated using only oily coatings on all canvases including linen soaked in oil to form an integrated whole with the oil color layer on top so that it could prolong the life of oil paintings. This absurd approach became one of the reasons for many 19th-century oil paintings becoming darkened and cracked damaged over time. The extreme practice of soaking linen fibers in oil also greatly shortened the life of linen fibers themselves because people at that time did not yet understand that oil dried by oxidation would continue to oxidize and deteriorate over time; its chemical stability was actually lower than that of various gelatins.

In China''s oil painting industry five or six decades ago also used pure oil canvases which were generally coated with zinc barium white (lithopone) with resin-based paint such as matte paint; however, paintings on these canvases have mostly become darkened over time even if they were not soaked in oil from behind they have turned into dark brown color which is very brittle and fragile.

Therefore, pure oily gesso has been eliminated today except for Rubens'' method mentioned above.

The so-called tempera gesso is a coating made by mixing a "oily glue" made by artificial manufacturing with paint mixtures at high temperatures into an emulsion-like gelatinous state which is difficult to master; then put oil into a bottle adding an appropriate amount of ammonium carbonate solution (or ammonia water) shaking and emulsifying it so that it can easily combine with various glue solutions; using this kind of emulsified glue mixed into coating material to make canvas is called tempera gesso.

Another feature of modern synthetic adhesive should be noted: generally speaking, most products are mainly produced as adhesives for objects rather than binding agents for coatings; sometimes chemical anti-aging agents need to be added to increase toughness and prevent brittleness; therefore coatings formed from too thick synthetic adhesive solutions will sometimes adhere only to fiber fluff on top of linen fabric like a layer of plastic sheet instead of forming an integrated whole; furthermore over time oil color layers become brittle due to oxidation while overly thick synthetic adhesive coatings often do not age simultaneously; this increases the risk of damaging oil painting life span.

Therefore whether using synthetic adhesive to mix canvas coating material or traditional animal glue to mix canvas coating material one must pay attention to the correct gelatinous formula; just like a friend named Del MacLaren (a 17th-century doctor who wrote a lengthy manuscript on Rubens'' techniques and art materials) said: "The bottom is crucial."

The above principles also apply completely to selecting raw canvas materials or commercial finished canvases; especially knowing how to check them based on their coating gelatinous formula will avoid falling into misconceptions.

With the rapid development of China''s oil painting industry in recent years many canvas manufacturers have emerged offering various sizes of branded or unbranded canvases including raw cloth rolls finished cloth rolls or framed canvases which provide more choices for painters than before; however these factories vary in size production methods causing significant differences in canvas quality; small workshops often use hand-made coatings improper coating mixture hasty brushing process unstable coatings etc.; individual manufacturers even use low-grade textiles and cheap industrial coatings lowering product quality even more so.

Some canvases may look clean white and flexible but they are actually produced for low-end commodity painting requiring mass production often using synthetic fabrics with gelatinous formulas that are generally too high; they may be suitable for beginners'' exercises but long-term storage will cause problems.

European commercial canvases are mostly produced by large automated assembly lines which guarantee stable canvas quality; generally speaking production lines consist of machines such as fabric flattening grinding machines with widths greater than two meters several large roller coaters drying machines strict requirements on workshops equipment and workers'' skills etc.

Most canvas products are produced on large-scale automated production lines, which offer the advantage of ensuring consistent canvas quality. These production lines typically consist of wide-width fabric flattening and polishing machines, as well as a set of three to four large roller coating machines and dryers. The requirements for factory space, equipment, and worker skills are quite stringent. Currently, there are domestic manufacturers in China that meet international industry standards and have established large-scale production lines. The largest among them is Phoenix Art Materials Group located in Jiangsu, which has built three canvas production line bases in Wuxi, Muyang, and Ho Chi Minh City, Vietnam. However, for over a decade, their main focus has been fulfilling foreign orders and exporting products to European and American countries. Some of their high-end canvases, as per the request of international clients, use rain-washed linen fabric sourced from the cold regions of Belgium and high-quality cotton fabric from India, with high-quality acrylic coatings. Varieties such as the coarse rain-washed linen canvas (E5317), fine rain-washed linen canvas (E5318), domestically produced pure linen canvas (E6024), pure natural cotton canvas (E5305), and twill cotton canvas (E5319) showcase excellent appearance and suitable adhesive ratios, providing artists with a comfortable painting experience that meets the quality standards of artist-grade canvas.

Furthermore, in the near future, Phoenix Art Materials plans to introduce various canvas varieties with different levels of absorbency, as well as canvases with pre-applied color grounds. They also have plans to offer customized services to cater to specific requirements of individual artists, aiming to meet the diverse needs of the oil painting industry. With the abundant supply of domestically produced canvases that guarantee stable quality, it will greatly benefit oil painters and contribute to the flourishing development of the art of oil painting overall, and may also lead to an improvement in the global standard of canvas manufacturing.