The application of indirect electrolysis as a reduction technique in indigo dyeing is described. Various reversible redox systems were tested to determine whether they are suitable for indigo dyeing. The results of the dyeing trials confirm that the process engineering involved can be applied to the production of denim. The new process offers environmental benefits and offers the prospects of improved process stability, because the reduction state in the dyebath can be readily monitored by measuring reduction potential.

The article contains sections titled: 1. History, Economic Importance 1.1. Historical Dyeing Methods 1.2. Economic Importance of Textile Dyeing 2. Dyeing Technology 2.1. General 2.1.1. History 2.1.2. The Field of Dyeing Technology 2.1.3. Fundamental Principles of Dyeing 2.1.3.1. Dyeing Systems 2.1.3.2. Phases of Exhaustion Dyeing 2.1.3.3. Dyeing Phase (Dyeing Kinetics) 2.1.3.4. Equilibrium Phase 2.1.3.5. Dye Fixation, Improvement of Colorfastness 2.1.3.6. Sources of Further Process Data 2.2. Batchwise Dyeing (Bath Dyeing) 2.2.1. Fundamental Principles and Equipment 2.2.2. Theoretical and Technical Fundamental Principles 2.2.3. Circulating Machines (Stationary Goods, Circulating Liquor) 2.2.3.1. Systems and Functions 2.2.3.2. Loose Stock Dyeing Machines 2.2.3.3. Package Dyeing Machines (Cross‐Wound Packages) 2.2.3.4. Hank Dyeing Machines 2.2.3.5. Beam Dyeing 2.2.4. Circulating‐Goods Machines with Textile Storage (Winch Type) 2.2.4.1. System and Functions 2.2.4.2. The Winch Beck 2.2.4.3. Jet Dyeing Machines 2.2.4.4. Overflow Dyeing Machines 2.2.4.5. The Air Jet (“Airflow”) Dyeing Machine 2.2.5. The Dyeing Jigger 2.2.5.1. Normal (Direct) Jig Dyeing 2.2.5.2. Pad Jig Process 2.2.6. Special Bath Dyeing Equipment 2.2.6.1. Star‐Shaped Dyeing Frames 2.2.6.2. Machines for Dyeing Hanks of Yarn 2.2.6.3. Paddle Dyeing Machine 2.2.6.4. Rotary Dyeing Machine 2.2.6.5. Cabinet Dyeing 2.2.6.6. Hosiery Dyeing Machines 2.2.7. Automatic Control of Bath Dyeing 2.2.7.1. Aims 2.2.7.2. Functions of Automatic Control 2.2.7.3. Equipment Requirements 2.3. Continuous and Semicontinuous Dyeing 2.3.1. The Principal Stages of Continuous Dyeing 2.3.1.1. Dye Pickup 2.3.1.2. Intermediate Drying 2.3.1.3. Dye Fixation 2.3.1.4. Aftertreatment of the Dyed Fabric (Finishing) 2.3.2. Dyeing Plants 2.3.3. Continuous Dyeing of Yarn and Fiber 2.3.4. Automatic Operation of Continuous Dyeing Plants 2.3.4.1. Important Process Stages and their Automation 2.3.4.2. Technology of Automation 2.4. Laboratory Dyeing Techniques 2.4.1. Objectives 2.4.2. Laboratory Dyeing 2.4.2.1. Typical Laboratory Equipment 2.4.2.2. Small‐Scale Production Equipment 2.4.3. Laboratory Dyeing Technology 2.5. Techniques of Dispensing Products used in Dyeing 2.5.1. Dispensing of Dyes 2.5.2. Dispensing of Dye Auxiliaries 2.5.3. Dispensing of Chemicals 2.5.4. Preparation of the Initial Liquor Charge and its Replenishment 2.5.4.1. Batch Dyeing 2.5.4.2. Continuous Dyeing 2.6. Colorimetry 2.6.1. Measuring Instruments 2.6.2. Methods of Expressing Colorimetric Results 2.6.3. Developments in Colorimetry 3. Physical Properties of Textiles Important for Dyeing 3.1. Classification of Textile Properties 3.2. Fibers 3.3. Yarns 3.4. Fabrics 3.5. Makeup of Textiles for Dyeing 4. Dyeing of Cellulose Fibers 4.1. Dyeing with Reactive Dyes 4.1.1. Fundamentals 4.1.2. Dyeing Techniques 4.1.3. Special Processes and Development Trends 4.2. Dyeing with Direct Dyes 4.2.1. Applications and Properties 4.2.2. Dyeing Principle 4.2.3. Pretreatment of Substrates 4.2.4. Dyeing Parameters 4.2.5. Dyeing Techniques 4.2.6. Special Processes 4.2.7. Aftertreatment 4.3. Dyeing with Anthraquinone Vat Dyes 4.3.1. Chemistry of Vat Dyes 4.3.2. Vatting 4.3.3. Dye Absorption in the Exhaustion Process 4.3.4.

The article contains sections titled: 1. Dyeing with Reactive Dyes 1.1. Fundamentals 1.2. Dyeing Techniques 1.3. Special Processes and Development Trends 2. Dyeing with Direct Dyes 2.1. Applications and Properties 2.2. Dyeing Principle 2.3. Pretreatment of Substrates 2.4. Dyeing Parameters 2.5. Dyeing Techniques 2.6. Special Processes 2.7. Aftertreatment 3. Dyeing with Anthraquinone Vat Dyes 3.1. Chemistry of Vat Dyes 3.2. Vatting 3.3. Dye Absorption in the Exhaustion Process 3.4. Oxidation 3.5. Aftertreatment (“Soaping”) 3.6. Dyeing Techniques 4. Dyeing with Indigo 4.1. Chemistry and Historical Development 4.2. Dyeing Technique 5. Dyeing with Sulfur Dyes 5.1. Types and Mode of Reaction 5.2. Additives to the Dye Bath 5.3. Dyeing 5.4. Dyeing Techniques 5.5. Combination with Other Dye Groups 5.6. Wastewater 6. Dyeing with Naphtol AS Dyes 7. Dyeing with Pigments 8. Other Dyeing Methods 8.1. Dyeing with Leuco Esters of Vat Dyes 8.2. Dyeing with Mordant Dyes 8.3. Dyeing with Acid Dyes 8.4. Dyeing with Basic Dyes 8.5. Dyeing with Mineral Dyes 8.6. Dyeing with Oxidation Dyes 8.7. Dyeing with Phthalogen Dyes 8.8. Dyeing with Coupling and Diazotization Dyes 9. Other Plant Fibers