The dry cylinder method (invisible color) of dyeing with还原dyes mainly has 8 major influencing factors. 

I. Dye Selection: 

For dyeing, it is advisable to use dyes with good uniformity. For immersion dyeing, due to the large liquid volume and for the convenience of operation, in addition to the dyes suitable for full bath reduction, generally dry cylinder reduction is used. When doing color matching, dyes with the same dyeing methods should be selected. The chromophore of the reducing dye has strong hydrogen bonds and intermolecular forces, high affinity, and high initial dyeing rate. To reduce uneven dyeing and the phenomenon of white core, the initial dyeing rate of the reducing dye must be controlled. 

II. Sodium hydroxide dosage: 

The functions of caustic soda are as follows: Firstly, it neutralizes the sodium bisulfite produced during the decomposition of the developer, preventing changes in the pH of the dye bath. Secondly, it ensures the complete reduction and dissolution of the dyes. In a strongly alkaline environment, the chromophores of the dyes can remain stable. Therefore, the amount of caustic soda in the dye bath (including the amount of caustic soda in the drying cylinder) is often higher than the theoretical amount. Insufficient caustic soda usage results in incomplete dye dissolution, and some dyes may even undergo abnormal reactions. Generally, dyes with a greater tendency to aggregate have a higher alkaline concentration. Conversely, the alkaline concentration can be lower. However, the amount of caustic soda should not be excessive either, as excessive caustic soda can easily aggregate at low dyeing temperatures, or the dyes may be overly dissolved in the dye solution, resulting in a low dyeing percentage and dull color. 

III. Amount of Potassium Permanganate: 

The concentration of the developer during the dyeing process depends on the dyeing depth, temperature, time, and bath ratio. It is also necessary to consider the conditions of the dyeing equipment and the ventilation status of the workshop. If the dyeing equipment is prone to causing the decomposition of the developer, the concentration should be higher; conversely, the concentration can be lower. Generally, the amount of developer is 2 to 5 times larger than the theoretical amount. During the dyeing process, it is necessary to appropriately supplement (add) the developer to ensure that the dye is always dyed under fully reduced conditions. Insufficient use of the developer will result in light colors, color bleeding defects, and a decrease in water washing fastness. However, it is not advisable to use too much either, as excessive use is not only wasteful but also causes the color to lose its brightness. 

IV. Dyeing Temperature: 

The dyeing temperature has a significant impact on the dyeing rate, dyeing percentage, uniformity and the dosage of baking powder. The effect varies depending on the type of dye. Generally, for dyes with a lower tendency for colorless bodies to aggregate, the diffusion rate is higher, the dyeing temperature is lower, and increasing the temperature will actually reduce the dyeing percentage; for dyes with a higher tendency to aggregate, the diffusion rate is lower, and a higher dyeing temperature is required during the dyeing process to increase the dye diffusion rate and uniformity. However, for some dyes, such as Red Blue RSN, excessive dyeing at high temperatures can lead to excessive reduction reactions. Additionally, high-temperature baking powder is unstable, so the dyeing temperature should not exceed 65℃. For those requiring high-temperature dyeing, the dosage of baking powder should be appropriately increased. 

V. Dyeing Time: 

The dyeing time has a significant impact on uniform dyeing, dyeing fastness, and dye uptake percentage, etc. A shorter dyeing time results in a lower dye uptake percentage, insufficient uniform dyeing, and poor dye fastness; however, an excessively long dyeing time, while providing good uniformity and dye fastness, also increases the consumption of dyeing accelerator. Generally, a dyeing time of 30 to 45 minutes is sufficient. 

VI. Electrolyte dosage: 

The tendency of dye chromophore aggregation varies, and the effects on salt or alumina powder also differ. For those with a lower degree of aggregation, a small amount of salt can be added to the dye bath to increase the dyeing percentage, but the dosage should not be excessive, generally 10% to 15% of the weight of the dyeing material. For those with a higher degree of aggregation, the affinity and dyeing percentage are generally higher, and no additional salt is needed. For the chromophores dyed by methods B and C, their affinity for the fibers is low. To increase the dyeing percentage, an appropriate amount of electrolyte can be added. 

VII. Dyeing bath ratio: 

The ratio of the dye bath is related to the percentage of dyeing, the amount of dyeing agent used, and the dyeing equipment. A larger bath ratio is conducive to even dyeing, but the percentage of dyeing increases and the consumption of dyeing agent also rises. A smaller bath ratio results in a higher concentration, causing some dyes to be poorly dissolved, forming color precipitates that adhere to the fiber surface, and easily causing streaking. The best dyeing should use soft water. For dyes sensitive to calcium hardness, they may undergo coagulation and precipitation when encountering hard water, and after dyeing, color spots may occur. 

VIII. Bleaching Agent: 

For dyes with high affinity for fibers, the initial dyeing rate is high, but the dyeing is prone to unevenness. During dyeing, a leveling agent such as Ping Ping Jia or cowhide glue is often added. Ping Ping Jia O can form complexes with the colorless bodies of the dye in the dye bath, gradually releasing the colorless bodies to dye the fibers as the dyeing process progresses. This reduces the dyeing rate of the dye and has a leveling effect. Cowhide glue is a high-molecular animal protein that can form protective colloids in the dye solution, increasing the viscosity of the dye solution and slowing down the adsorption speed of the dye to the fibers, achieving a leveling effect. The dosage of Ping Ping Jia O is generally 0.1 to 0.5 g/L, and the dosage of cowhide glue is 1 to 4 g/L. In color matching, sometimes two different leveling agents can be used. The dosage of the leveling agents should not be too high, otherwise the dye will remain in the dye solution, reducing the dyeing percentage.