Scarlet Acid

Updated: 2026-08-01

Overview

Scarlet Acid (C.I. Acid Red 73) is a synthetic azo dye first developed in the early 20th century for textile applications. As an acid dye, it bonds effectively to protein-based fibers like wool and silk, as well as to nylon. The compound's intense red coloration and stability under acidic conditions made it particularly valuable for industrial dyeing processes. Modern production of Scarlet Acid follows strict quality control measures to ensure batch-to-batch consistency in shade and solubility. While its usage has declined somewhat due to environmental concerns, it remains important for specific applications where its color properties are unmatched by alternatives.

Physical and Chemical Properties

Scarlet Acid presents as a reddish-brown crystalline powder with good water solubility (approximately 50 g/L at 20°C). Its color appears more vibrant in solution, producing a brilliant scarlet hue at optimal concentrations. The dye exhibits moderate lightfastness (rating 4-5 on the Blue Wool Scale) and fair wash fastness on protein fibers. Chemically, it behaves as a typical aromatic sulfonic acid, with two sulfonate groups contributing to its water solubility and anionic character. The azo linkage (-N=N-) in its structure is responsible for the chromophoric properties. Under strong reducing conditions, this bond can cleave, causing color loss - a consideration for certain industrial processes.

Main Applications

The primary use of Scarlet Acid remains in textile dyeing, particularly for wool, silk, and nylon fabrics. Its bright shade and good leveling properties make it suitable for both piece dyeing and yarn applications. The dye is often used in combination with other acid dyes to achieve specific color shades in carpet and apparel manufacturing. Beyond textiles, Scarlet Acid finds application in the production of red inks for stamp pads and certain printing applications. In biological laboratories, it serves as a histological stain for specific tissue components. Some specialized paper products and leather goods also utilize this dye for its color properties.

Safety and Storage

As with many synthetic dyes, Scarlet Acid requires careful handling to minimize exposure. Dust inhalation should be prevented through proper ventilation or respiratory protection. The compound may cause mild skin irritation, necessitating gloves during handling. For storage, keep containers tightly sealed in a cool, dry environment away from strong oxidizers. Bulk quantities should be protected from moisture to prevent caking. Shelf life typically exceeds two years when stored properly. Spills should be contained and cleaned promptly with appropriate personal protective equipment.

B2B Procurement Guide

Industrial buyers should specify required parameters including dye content (typically 80-95%), salt content, and solubility characteristics. Reputable suppliers will provide certificates of analysis with each batch. For textile applications, verify the dye's compatibility with specific fiber types and dyeing processes. Purchasing considerations should include: minimum order quantities (often 25kg for industrial buyers), packaging options (drums vs. bags), and supplier certifications for quality management systems. Price negotiations often depend on order volume and long-term supply agreements. Sample testing is recommended before large purchases to confirm color matching and performance.