One, bluegrass

Indigo is oxidized from indoxyl, so any plant containing free indoxyl and indoxyl can be used to produce indigo.
​An annual herb named Persicaria tinctoria. Its stems and leaves contain indigoside, this substance after hydrolysis and fermentation, can produce colorless water-soluble 3-hydroxy-indoxyl, that is, indigowhite, when indigowhite by the sun, air oxidation after condensation into a dyeing function of indigo. Among all kinds of plant dyes used in ancient times, it was the earliest and the most used. The history of the use of bluegrass dyeing in China can be traced back to at least the Zhou Dynasty more than two tSophora refers to the buds and open flowers of the sophora tree, a leguminous plant. Locust yellow green, shape like rice, so it is also called locust rice.
housand years ago. In the Book of Songs, the lines "the final dynasty picks blue, not a surplus 襜" show that people in the Spring and Autumn period did collect bluegrass for dyeing.
​In the Book of Rites · Yue Ling, there is also a narrative of "midsummer, so that the people do not dye blue", indicating that between the Warring States and the Han Dynasty, people not only dyed blue grass, but also planted it in large quantities for harvest, and stipulated that they were not allowed to pick it randomly until the time of cutting. After the Western Han Dynasty, planting bluegrass gradually became a speciaSix, locust flowerslty in agricultural production.

Two, madder grass

The main chemistry of madder is anthraquinone and its glycosides.
​Madder grass, also known as ru 藘 and MAO search (" Erya "), is a plant dye used for a long time in ancient China. Before the Warring States period, it was a wild plant.
​In the Book of Songs, "Ru 藘 in the han" and "Ji yi ru 藘", the former means that it grows on the hillside, the latter means that it is dyed. Since the Western Han Dynasty, a large number of artificial planting began, Sima Qian said in the "Records of the Grand Historian", if the emerging large landowners planted "ten mu Zhi Qian", its income can be as "a thousand households." Madder is a perennial climbing herb that can be harvested in spring and autumn (the quality of the autumn harvest is good). After harvest, dry storage, can be cut into pieces when dyeing, boiled in hot water.
​Madder is a mordant dye, and the main components of the pigments are alizarin and purpurin. If it is directly used for dyeing, it can only be dyed light yellow plant color, while adding mordant can be dyed red, crimson and other red tones. Unearthed cultural relics prove that the mordant used in ancient times is mostly alum containing more aluminum ions. This is because the reaction of aluminum hydroxide and alizarin produced after the hydrolysis of alum can produce a red precipitate with bright color and good adhesion. The red background color of the "deep red silk" and "Long life embroidered robe" unearthed at the No. 1 Han Tomb in Mawangdui, Changsha, was soaked with alizarin and alum several times by laboratory tests.

Three, red flower

The cultivation and preparation of safflower dye were recorded in Jia Sixie's Qimin Yaoshu in Northern Wei Dynasty.
​Safflower, also known as red and blue flowers, is an herb with red and yellow flowers in summer, native to Northwest China. In the Western Han Dynasty, it began to spread to the mainland. Safflower is suitable for direct dyeing of a variety of fibers, and is one of the most vivid colors in red vegetable dyes. The red color dyed with it is called true red or scarlet, and the poem "red flower color covers thousands of flowers, any orangutan blood is not added" in Tang Dynasty poetry vividly summarizes the red flower color.

Four, sapwood

Sumu formerly known as Su Fang, Li Shizhen "Compendium of Materia Medica" said, "the island has Su Fang country, its property this wood, so the name." In fact, this evergreen tree plant belonging to the leguminous family has always grown in Yunnan, Guangdong, Guangdong and Taiwan. And as early as the Western Jin Dynasty, the southern area of the folk, it has been widely used dyeing. The colorless protopigment contained in the ochre brown hearthwood of hematoxylin is called "Basi hematoxylin", which becomes colored "Brazilian hematoxylin" by air oxidation.
​Sapwood is a mordant dye, and the color of the dyed fabric depends on the mordant used. General chrome mordant is purple to purple; Aluminum mordant to red, copper mordant to red brown; Iron mordant brown; Tin mordant is light red to deep red, and the red color of hemwood is very close to the red color of Shu red brocade and Guangxi brocade dyed with safflower.

Gardenia

Its pigment components are mainly terpenoid saffron and flavonoid gardenia yellow. Gardenia pigment can be used to dye the fabric yellow and slightly red.Gardenia evergreen shrub with white flowers. The main component of the pigment used as a dye in the fruit is gardenin. The fruit is first soaked in cold water and then boiled to produce yellow dye. This dye is a direct dye, can be directly dyed on silk, hemp, cotton and other natural plants, can also be mordant for mordant, get different color light, such as: chromium mordant gray yellow; Copper mordant bright yellow; Iron mordant is dark yellow. Because of its convenient dyeing and bright light, it has been the most widely used yellow vegetable dye in the Central Plains since the Qin and Han Dynasties.

Six, locust flowers

Sophora refers to the buds and open flowers of the sophora tree, a leguminous plant. Locust yellow green, shape like rice, so it is also called locust rice.
​Sophora flowers contain a kind of mordant pigment rutin, can interact with a variety of mordant, dye a variety of different colors. If with tin mordant bright yellow; Aluminum mordant is straw-yellow; Chrome mordant is gray-green.

Seven, Yu JinA perennial herb of the ginger family having underground tubers and fusiform fleshy roots, yellow in cross section and fragrant, occurring mainly in southern and southwestern China. Dyeing is to use the boiling liquid after soaking the fleshy root, adding metal salts other than iron to dye, you can dye a variety of yellow colors. "Compendium of Materia Medica" records: "Yu Jin sheng Shu and the western regions, dyeing is with its stems. Dyed women's clothes are bright, but they are not able to tolerate sunburn, and there is a slight air of stagnation gold." It shows that the ancient folk had long been familiar with the characteristics of Yujin, and was widely used in women's fabric coloring. This is the earliest clothing dyeing material with fragrance in China.

8. Smoke treeCotinus, also known as cotinus, deciduous plants of the sumac family, distributed in the northeast and central parts of China, wood can be made of utensils, and used to extract yellow dyes. According to "Tiangong Kai Wu" records: first with smoke wood decocting water dye, and then with hemp straw ash leached out of the alkali water rinsed. The wood contains a pigment called fisetin, which gives it a reddish yellow in daylight and a reddish red in candlelight. This mysterious light color difference makes it the most noble color dye, which has been "the Son of Heaven" since Sui to Ming.

9. Cascara

Rhamnus, also known as the stinking plum, is a deciduous shrub or small joben found in the northeast and central regions of China. Its fruit and stem skin contain emodin, aloe emodin and other pigments, is an excellent natural green dye. When dyeing, you only need to boil the tender fruit or stem skin in water to make dye solution, and dye the fabric in weak acid or weak alkaline dye solution to obtain green fabric with good color fastness, light resistance, acid resistance and alkali resistance, such as the use of reducing agent in weak acid solution, reduction dyeing, but also can make blue green.

Ten, comfrey

Compost, perennial herb, strong roots, dark purple appearance, purple cross section, containing purple crystalline substance acetyl compost quinone (Kukun), can be used as purple dye. In ancient times, comfrey was also known as "Erya" (Erya). Tao Hongjing said, "Most of the people in Xiangyang are coming from Xinye, Nanyang, and the purpured-colored person is one of them." Li Shizhen said: "comfrey flower purple root purple, can be dyed purple, hence the name." Shikonin is also a mordant dye, without mordant, silk wool and hemp fiber are not colored, and the interaction with the mordant containing more aluminum such as toon wood ash and alum can obtain purple red.
​​​In addition to the above plants, plants containing tannin such as wolftail, sage and gallnut were used as the main materials for blackening in ancient times.

11. Gallnut

Gallnut, also known as Baizhicang, Baiyao decoction, gallnut, in ancient times known as "no food", "oak gallnut", the color of gallnut is similar to bluegrass deep dye of the blue black, the color of gallnut also need to be dyed by iron compounds, but different iron compounds will produce different colors and chromaticity, the same as gardenia, gallnut color depth is also controlled by the acidity. Ferrous mordant will make the color of the gallnut tend to blue black, but the use of iron acetate as a mordant will produce gray pigment that does not tend to any color system, and will get black hue after deep dyeing.

Preparation and preservation of vegetable dyes
There are two ways to use vegetable dyes in ancient China: one is to directly use the fresh leaves of vegetable dyes, that is, to place the fabric to be dyed in the dye solution with its fresh leaves and has been fermented, or soak or boil for a period of time to make the fabric colored; One is to make the pigments in the fresh leaves of plant dyes ready for dyeing through chemical processing. The former method of dyeing is limited by the season, because the plant pigment is difficult to preserve in the plant for a long time, and the fresh leaves picked must be soaked with the fabric in time, otherwise it will lose the dyeing value. Therefore, in the production technology is relatively backward from the Shang and Zhou dynasties to the Warring States period, dyeing can only be carried out in summer and autumn, such as blue dyeing and blue picking must be in June to July, red dyeing and madder root digging must be in May to September, and other grass dyeing and dyeing are also mostly in autumn. The latter method because the pigment is made out, the dye will not fail for a long time, the dyeing can be carried out at any time, and there is no need to rob the season to cut grass and dye, so the amount of vegetable dyes is mostly used this method.
​​​In ancient China, there were many scientific methods for purification and storage of various vegetable dyes, some of which had the same technological principles as those used in modern times. Some methods are still in use today because of their simplicity and practicality, such as the preparation and preservation of indigo and safflower.
It is not recorded when the technology of manufacturing indigo in China was invented, and it is estimated that it will not be later than this period from the large-scale cultivation of bluegrass in the Qin and Han dynasties, and it will be fully mature after The Three Kingdoms. Jia Sixie in the Northern Wei Dynasty recorded the method of making indigo with bluegrass at that time in his book "Qi Min Yao Shu" : "Cut blue in the vertical pit, water", and suppress the bluegrass with wood or stone to make it all immersed in water. Impregnation time is "hot overnight, cold overnight". Then the leaching solution is filtered, placed in a VAT, and then lime is added to the filtrate in the proportion of 1.5%, and the filtrate is rapidly agitated with a stick to accelerate the combination of indigoside in the solution and oxygen in the air, to be precipitated, "clarified and drained water", another "small pit for indigo storage", and then when its water evaporates to "such as strong porridge", then "indigo into". In this paper, not only the method of making indigo, but also the proportion of bluegrass and lime used were described. Since the Tang and Song dynasties, many books have discussed the methods of indigo production, of which the most familiar is the Ming Dynasty Song Yingxing's "Tiangong Kai Wu" said: when indigo production, leaves and stems into the cellar when the amount is large, the amount is small into the bucket and VAT. After seven days of soaking in water, the blue juice comes out. Each stone slurry, put five liters of lime, beat dozens of times, and the indigo will condense. When the water is still, indigo is deposited on the bottom. The content is basically the same as Jia Shu, but some places are more detailed. The bluegrass water immersion time is much more than the former, which is mainly to increase the production rate of indigo, and of course, it also has more scientific.
​​In the use of chemically processed indigo dyeing, it is necessary to first put indigo into the acidic solution, and add an appropriate amount of lees, and then after a period of fermentation, that is, become the dye; The fabric that needs to be dyed is immersed in dyeing, and after the dye is taken out, it is blue by the sun, and the dyeing mechanism is that the hydrogen (and carbon dioxide) produced in the fermentation process of the lees can reduce indigo to indigo white. Indigo white can be dissolved in an acidic solution, so that the fiber color. After the fabric has been impregnated, it has been in contact with the air for a period of time after coming out of the tank, and it will show a bright blue color due to oxidation. This process of making indigo and dyeing with it has sufficient scientific basis, and is completely consistent with the dyeing mechanism of modern synthetic indigo.
​​Safflower contains two pigments, yellow pigment and red pigment, of which only red pigment has dyeing value. The red pigment exists in the form of carthamin in safflower. The method of extracting carthamin in modern chromaticity is to make use of the characteristics that both red pigment and yellow pigment are soluble in alkaline solution, red pigment is insoluble in acidic solution, and yellow pigment is soluble in acidic solution. First, both pigments were leached from safflower with alkaline solution, and then neutralized with acid, so that only the safflower with fluorescence was precipitated. In fact, China has been using this characteristic of safflower to purify and dye red in various periods since the Han Dynasty. "Qi Min Yao Shu" has a detailed description of the folk processing of safflower dye. The general content is: first mashed safflower, slightly fermented, rinsed with water, twisted yellow juice with a cloth bag, soaked in grass and wood ash for some time, then added to the fermented millet pulp in the same soak, and then twisted with a cloth bag, ready for dyeing. The plant ash is an alkaline solution, while the fermented rice pulp is acidic. In addition, in order to make the color of red flowers more vivid, the ancients also used acidic plum water to replace the fermented millet rice pulp (" Tiangong Kai Wu "). It can be seen that the method of producing carthamin in ancient China is completely consistent with the principle of modern extraction.
​​​It is particularly worth pointing out that in ancient China, not only can red flowers be used for dyeing, but also the red pigment that has been attached to the dyed fabric can be extracted again and used repeatedly. This is clearly recorded in the "Tiangong Kai Wu" : "Where red flowers dyed silk, if you want to turn, but soaked the dyed silk, with alkaline water, rice ash water droplets on dozens of drops, its red ten cents turn, still reduce the quality, the collected water hidden in the green bean powder, and then released the dye tank, half drop is not consumed." This account may sound incomprehensible, but there is a reason for it. This is to use the characteristics of safflower red pigment soluble in alkaline solution, it is re-leached from the dyed fabric. As for its storage in mung bean powder, it is to use mung bean powder as an adsorbent of safflower. This also shows that the dyeers at that time not only understood the dyeing characteristics and properties of safflower, but also were extremely skilled in the utilization of safflower technology.

One, bluegrass

Indigo is oxidized from indoxyl, so any plant containing free indoxyl and indoxyl can be used to produce indigo.
​An annual herb named Persicaria tinctoria. Its stems and leaves contain indigoside, this substance after hydrolysis and fermentation, can produce colorless water-soluble 3-hydroxy-indoxyl, that is, indigowhite, when indigowhite by the sun, air oxidation after condensation into a dyeing function of indigo. Among all kinds of plant dyes used in ancient times, it was the earliest and the most used. The history of the use of bluegrass dyeing in China can be traced back to at least the Zhou Dynasty more than two tSophora refers to the buds and open flowers of the sophora tree, a leguminous plant. Locust yellow green, shape like rice, so it is also called locust rice.
housand years ago. In the Book of Songs, the lines "the final dynasty picks blue, not a surplus 襜" show that people in the Spring and Autumn period did collect bluegrass for dyeing.
​In the Book of Rites · Yue Ling, there is also a narrative of "midsummer, so that the people do not dye blue", indicating that between the Warring States and the Han Dynasty, people not only dyed blue grass, but also planted it in large quantities for harvest, and stipulated that they were not allowed to pick it randomly until the time of cutting. After the Western Han Dynasty, planting bluegrass gradually became a speciaSix, locust flowerslty in agricultural production.

Two, madder grass

The main chemistry of madder is anthraquinone and its glycosides.
​Madder grass, also known as ru 藘 and MAO search (" Erya "), is a plant dye used for a long time in ancient China. Before the Warring States period, it was a wild plant.
​In the Book of Songs, "Ru 藘 in the han" and "Ji yi ru 藘", the former means that it grows on the hillside, the latter means that it is dyed. Since the Western Han Dynasty, a large number of artificial planting began, Sima Qian said in the "Records of the Grand Historian", if the emerging large landowners planted "ten mu Zhi Qian", its income can be as "a thousand households." Madder is a perennial climbing herb that can be harvested in spring and autumn (the quality of the autumn harvest is good). After harvest, dry storage, can be cut into pieces when dyeing, boiled in hot water.
​Madder is a mordant dye, and the main components of the pigments are alizarin and purpurin. If it is directly used for dyeing, it can only be dyed light yellow plant color, while adding mordant can be dyed red, crimson and other red tones. Unearthed cultural relics prove that the mordant used in ancient times is mostly alum containing more aluminum ions. This is because the reaction of aluminum hydroxide and alizarin produced after the hydrolysis of alum can produce a red precipitate with bright color and good adhesion. The red background color of the "deep red silk" and "Long life embroidered robe" unearthed at the No. 1 Han Tomb in Mawangdui, Changsha, was soaked with alizarin and alum several times by laboratory tests.

Three, red flower

The cultivation and preparation of safflower dye were recorded in Jia Sixie's Qimin Yaoshu in Northern Wei Dynasty.
​Safflower, also known as red and blue flowers, is an herb with red and yellow flowers in summer, native to Northwest China. In the Western Han Dynasty, it began to spread to the mainland. Safflower is suitable for direct dyeing of a variety of fibers, and is one of the most vivid colors in red vegetable dyes. The red color dyed with it is called true red or scarlet, and the poem "red flower color covers thousands of flowers, any orangutan blood is not added" in Tang Dynasty poetry vividly summarizes the red flower color.

Four, sapwood

Sumu formerly known as Su Fang, Li Shizhen "Compendium of Materia Medica" said, "the island has Su Fang country, its property this wood, so the name." In fact, this evergreen tree plant belonging to the leguminous family has always grown in Yunnan, Guangdong, Guangdong and Taiwan. And as early as the Western Jin Dynasty, the southern area of the folk, it has been widely used dyeing. The colorless protopigment contained in the ochre brown hearthwood of hematoxylin is called "Basi hematoxylin", which becomes colored "Brazilian hematoxylin" by air oxidation.
​Sapwood is a mordant dye, and the color of the dyed fabric depends on the mordant used. General chrome mordant is purple to purple; Aluminum mordant to red, copper mordant to red brown; Iron mordant brown; Tin mordant is light red to deep red, and the red color of hemwood is very close to the red color of Shu red brocade and Guangxi brocade dyed with safflower.

Gardenia

Its pigment components are mainly terpenoid saffron and flavonoid gardenia yellow. Gardenia pigment can be used to dye the fabric yellow and slightly red.Gardenia evergreen shrub with white flowers. The main component of the pigment used as a dye in the fruit is gardenin. The fruit is first soaked in cold water and then boiled to produce yellow dye. This dye is a direct dye, can be directly dyed on silk, hemp, cotton and other natural plants, can also be mordant for mordant, get different color light, such as: chromium mordant gray yellow; Copper mordant bright yellow; Iron mordant is dark yellow. Because of its convenient dyeing and bright light, it has been the most widely used yellow vegetable dye in the Central Plains since the Qin and Han Dynasties.

Six, locust flowers

Sophora refers to the buds and open flowers of the sophora tree, a leguminous plant. Locust yellow green, shape like rice, so it is also called locust rice.
​Sophora flowers contain a kind of mordant pigment rutin, can interact with a variety of mordant, dye a variety of different colors. If with tin mordant bright yellow; Aluminum mordant is straw-yellow; Chrome mordant is gray-green.

Seven, Yu JinA perennial herb of the ginger family having underground tubers and fusiform fleshy roots, yellow in cross section and fragrant, occurring mainly in southern and southwestern China. Dyeing is to use the boiling liquid after soaking the fleshy root, adding metal salts other than iron to dye, you can dye a variety of yellow colors. "Compendium of Materia Medica" records: "Yu Jin sheng Shu and the western regions, dyeing is with its stems. Dyed women's clothes are bright, but they are not able to tolerate sunburn, and there is a slight air of stagnation gold." It shows that the ancient folk had long been familiar with the characteristics of Yujin, and was widely used in women's fabric coloring. This is the earliest clothing dyeing material with fragrance in China.

8. Smoke treeCotinus, also known as cotinus, deciduous plants of the sumac family, distributed in the northeast and central parts of China, wood can be made of utensils, and used to extract yellow dyes. According to "Tiangong Kai Wu" records: first with smoke wood decocting water dye, and then with hemp straw ash leached out of the alkali water rinsed. The wood contains a pigment called fisetin, which gives it a reddish yellow in daylight and a reddish red in candlelight. This mysterious light color difference makes it the most noble color dye, which has been "the Son of Heaven" since Sui to Ming.

9. Cascara

Rhamnus, also known as the stinking plum, is a deciduous shrub or small joben found in the northeast and central regions of China. Its fruit and stem skin contain emodin, aloe emodin and other pigments, is an excellent natural green dye. When dyeing, you only need to boil the tender fruit or stem skin in water to make dye solution, and dye the fabric in weak acid or weak alkaline dye solution to obtain green fabric with good color fastness, light resistance, acid resistance and alkali resistance, such as the use of reducing agent in weak acid solution, reduction dyeing, but also can make blue green.

Ten, comfrey

Compost, perennial herb, strong roots, dark purple appearance, purple cross section, containing purple crystalline substance acetyl compost quinone (Kukun), can be used as purple dye. In ancient times, comfrey was also known as "Erya" (Erya). Tao Hongjing said, "Most of the people in Xiangyang are coming from Xinye, Nanyang, and the purpured-colored person is one of them." Li Shizhen said: "comfrey flower purple root purple, can be dyed purple, hence the name." Shikonin is also a mordant dye, without mordant, silk wool and hemp fiber are not colored, and the interaction with the mordant containing more aluminum such as toon wood ash and alum can obtain purple red.
​​​In addition to the above plants, plants containing tannin such as wolftail, sage and gallnut were used as the main materials for blackening in ancient times.

11. Gallnut

Gallnut, also known as Baizhicang, Baiyao decoction, gallnut, in ancient times known as "no food", "oak gallnut", the color of gallnut is similar to bluegrass deep dye of the blue black, the color of gallnut also need to be dyed by iron compounds, but different iron compounds will produce different colors and chromaticity, the same as gardenia, gallnut color depth is also controlled by the acidity. Ferrous mordant will make the color of the gallnut tend to blue black, but the use of iron acetate as a mordant will produce gray pigment that does not tend to any color system, and will get black hue after deep dyeing.

Preparation and preservation of vegetable dyes
There are two ways to use vegetable dyes in ancient China: one is to directly use the fresh leaves of vegetable dyes, that is, to place the fabric to be dyed in the dye solution with its fresh leaves and has been fermented, or soak or boil for a period of time to make the fabric colored; One is to make the pigments in the fresh leaves of plant dyes ready for dyeing through chemical processing. The former method of dyeing is limited by the season, because the plant pigment is difficult to preserve in the plant for a long time, and the fresh leaves picked must be soaked with the fabric in time, otherwise it will lose the dyeing value. Therefore, in the production technology is relatively backward from the Shang and Zhou dynasties to the Warring States period, dyeing can only be carried out in summer and autumn, such as blue dyeing and blue picking must be in June to July, red dyeing and madder root digging must be in May to September, and other grass dyeing and dyeing are also mostly in autumn. The latter method because the pigment is made out, the dye will not fail for a long time, the dyeing can be carried out at any time, and there is no need to rob the season to cut grass and dye, so the amount of vegetable dyes is mostly used this method.
​​​In ancient China, there were many scientific methods for purification and storage of various vegetable dyes, some of which had the same technological principles as those used in modern times. Some methods are still in use today because of their simplicity and practicality, such as the preparation and preservation of indigo and safflower.
It is not recorded when the technology of manufacturing indigo in China was invented, and it is estimated that it will not be later than this period from the large-scale cultivation of bluegrass in the Qin and Han dynasties, and it will be fully mature after The Three Kingdoms. Jia Sixie in the Northern Wei Dynasty recorded the method of making indigo with bluegrass at that time in his book "Qi Min Yao Shu" : "Cut blue in the vertical pit, water", and suppress the bluegrass with wood or stone to make it all immersed in water. Impregnation time is "hot overnight, cold overnight". Then the leaching solution is filtered, placed in a VAT, and then lime is added to the filtrate in the proportion of 1.5%, and the filtrate is rapidly agitated with a stick to accelerate the combination of indigoside in the solution and oxygen in the air, to be precipitated, "clarified and drained water", another "small pit for indigo storage", and then when its water evaporates to "such as strong porridge", then "indigo into". In this paper, not only the method of making indigo, but also the proportion of bluegrass and lime used were described. Since the Tang and Song dynasties, many books have discussed the methods of indigo production, of which the most familiar is the Ming Dynasty Song Yingxing's "Tiangong Kai Wu" said: when indigo production, leaves and stems into the cellar when the amount is large, the amount is small into the bucket and VAT. After seven days of soaking in water, the blue juice comes out. Each stone slurry, put five liters of lime, beat dozens of times, and the indigo will condense. When the water is still, indigo is deposited on the bottom. The content is basically the same as Jia Shu, but some places are more detailed. The bluegrass water immersion time is much more than the former, which is mainly to increase the production rate of indigo, and of course, it also has more scientific.
​​In the use of chemically processed indigo dyeing, it is necessary to first put indigo into the acidic solution, and add an appropriate amount of lees, and then after a period of fermentation, that is, become the dye; The fabric that needs to be dyed is immersed in dyeing, and after the dye is taken out, it is blue by the sun, and the dyeing mechanism is that the hydrogen (and carbon dioxide) produced in the fermentation process of the lees can reduce indigo to indigo white. Indigo white can be dissolved in an acidic solution, so that the fiber color. After the fabric has been impregnated, it has been in contact with the air for a period of time after coming out of the tank, and it will show a bright blue color due to oxidation. This process of making indigo and dyeing with it has sufficient scientific basis, and is completely consistent with the dyeing mechanism of modern synthetic indigo.
​​Safflower contains two pigments, yellow pigment and red pigment, of which only red pigment has dyeing value. The red pigment exists in the form of carthamin in safflower. The method of extracting carthamin in modern chromaticity is to make use of the characteristics that both red pigment and yellow pigment are soluble in alkaline solution, red pigment is insoluble in acidic solution, and yellow pigment is soluble in acidic solution. First, both pigments were leached from safflower with alkaline solution, and then neutralized with acid, so that only the safflower with fluorescence was precipitated. In fact, China has been using this characteristic of safflower to purify and dye red in various periods since the Han Dynasty. "Qi Min Yao Shu" has a detailed description of the folk processing of safflower dye. The general content is: first mashed safflower, slightly fermented, rinsed with water, twisted yellow juice with a cloth bag, soaked in grass and wood ash for some time, then added to the fermented millet pulp in the same soak, and then twisted with a cloth bag, ready for dyeing. The plant ash is an alkaline solution, while the fermented rice pulp is acidic. In addition, in order to make the color of red flowers more vivid, the ancients also used acidic plum water to replace the fermented millet rice pulp (" Tiangong Kai Wu "). It can be seen that the method of producing carthamin in ancient China is completely consistent with the principle of modern extraction.
​​​It is particularly worth pointing out that in ancient China, not only can red flowers be used for dyeing, but also the red pigment that has been attached to the dyed fabric can be extracted again and used repeatedly. This is clearly recorded in the "Tiangong Kai Wu" : "Where red flowers dyed silk, if you want to turn, but soaked the dyed silk, with alkaline water, rice ash water droplets on dozens of drops, its red ten cents turn, still reduce the quality, the collected water hidden in the green bean powder, and then released the dye tank, half drop is not consumed." This account may sound incomprehensible, but there is a reason for it. This is to use the characteristics of safflower red pigment soluble in alkaline solution, it is re-leached from the dyed fabric. As for its storage in mung bean powder, it is to use mung bean powder as an adsorbent of safflower. This also shows that the dyeers at that time not only understood the dyeing characteristics and properties of safflower, but also were extremely skilled in the utilization of safflower technology.