Utilizing UV-Visible Spectroscopy for Color Analysis of Fabrics

Color Analysis of Fabrics by UV-Visible Spectroscopy — Application Note Summary

Significance of the topic

The visual color of textiles is a critical quality attribute across industries (textile manufacturing, defense, heritage conservation, QA/QC). Human assessment is subjective and variable; instrumental color measurement provides objective, reproducible metrics to quantify perceptible differences, monitor dye performance (color fastness), and support matching for applications such as camouflage or product quality control.

Study objectives and overview

- Demonstrate quantitative color analysis of dyes and commercially sourced fabrics using UV-Visible reflectance/absorbance spectroscopy and CIE color metrics.
- Compare CIE L*a*b* coordinates for direct dye solutions and for sets of cotton and polyester fabrics of visually similar colors to reveal subtle differences not obvious to the eye.
- Confirm fabric composition by FTIR to relate color results to material identity.

Methodology and measurement parameters

- UV-Visible absorption spectra were recorded for three direct dyes (Direct Blue 71, Direct Red 81, Direct Yellow 27) prepared in aqueous solution at concentrations chosen to give Abs < 1.
- Reflectance spectra of fabric samples (six colors each for cotton and polyester: white, black, red, blue, yellow, green) were measured in reflection mode with an integrating sphere; data reported as %R using a Spectralon white reference.
- Spectral collection settings: 780 to 380 nm, 1 nm bandwidth, 1 nm data interval, 0.30 s integration time.
- CIE color calculations used a D65 illuminant at 10° observer and followed USP <1061> and ASTM E308 procedures to compute L*, a*, b* and ΔE*ab.
- FTIR confirmation used ATR-FTIR with library correlation to verify cotton versus polyester.

Used instrumentation

• Thermo Scientific Evolution One Plus UV-Vis Spectrometer (absorbance and reflectance)
• Integrating sphere accessory ISA-220 for reflectance measurements
• Spectralon white disk as reference standard
• Thermo Scientific Insight Pro Software for CIE L*a*b* calculations
• Thermo Scientific Nicolet iS20 FTIR with iTX diamond ATR (16 scans, 4 cm⁻¹ resolution) and Omnic software for library searches

Key results and discussion

- Dye absorbance maxima: Direct Yellow 27 near 400 nm, Direct Red 81 near 512 nm, Direct Blue 71 near 586 nm, consistent with expected complementary-color absorption.
- Calculated CIE L*a*b* for dye solutions aligned with perceived colors: e.g., Direct Red 81 showed a large positive a* (reddish), Direct Blue 71 a large negative b* (blue), Direct Yellow 27 a large positive b* (yellow).
- Fabric reflectance spectra alone did not always make perceptible differences obvious; CIE L*a*b* calculations quantified differences.
- For the paired cotton (c) and polyester (p) samples, most color differences (ΔE*ab) were below or near the visual discrimination threshold (ΔE*ab ≈ 3), indicating samples would be visually indistinguishable. Exceptions:
- Sample pair 6c/6p (green fabrics) showed the largest difference: ΔE*ab ≈ 30.2, clearly perceptible and reflecting distinct hues between materials.
- Sample pairs 4 and 5 (blue and yellow variants) showed moderate ΔE*ab (≈6.7 and 6.66), where differences were mainly due to L* (lightness) shifts; when ΔL* was zeroed, perceptibility decreased.
- FTIR ATR spectra and library matching confirmed the nominal fabric compositions (cotton versus polyester), supporting interpretation that material properties (fiber type, dye-fiber interactions) influence final color coordinates and lightness.

Practical benefits and applications

- Provides an objective, reproducible workflow for textile color QC: measure reflectance spectra, compute CIE L*a*b*, and use ΔE*ab thresholds for pass/fail decisions.
- Useful for color matching, dye selection, monitoring color fastness (fading, washing effects), and validating camouflage or environment-matching textiles where subtle color differences matter.
- Combining spectrophotometry with FTIR adds material identification, helping diagnose whether color differences stem from dye chemistry or substrate effects.

Limitations noted

- Reflectance measurements are relative to the white standard; highly reflective whites may exceed the reference reflectance, affecting absolute %R values.
- Color differences can arise from lightness (L*) shifts or from chromaticity (a*, b*); root causes (dye concentration, dye-fiber affinity, finishing, surface texture) require further analytical follow-up beyond colorimetry.

Future trends and potential applications

- Increasing use of portable and handheld spectrophotometers for in-field color QC and on-site textile assessment.
- Integration of hyperspectral imaging and spatially resolved colorimetric mapping to assess dye uniformity and localized defects.
- Application of chemometric models to relate spectral signatures to dye chemistry, degradation state, or processing variables for predictive QA/QC.
- Enhanced workflows combining colorimetry, FTIR, and other molecular techniques (e.g., Raman, mass spectrometry) for comprehensive fabric/dye forensic and provenance analyses.
- Adoption of standardized color tolerances in supply chains, and automated monitoring for sustainable dye selection and reduced rework.

Conclusion

The application note demonstrates that UV-Visible spectroscopy combined with standardized CIE color metrics (L*, a*, b*, ΔE*ab) provides robust, quantitative assessment of textile color. Using an integrating-sphere reflectance approach and a defined illuminant/observer condition enables detection and quantification of subtle color differences between fabrics of different fiber types. Coupling colorimetry with FTIR material identification enhances interpretation and supports QA/QC, forensic, and product development workflows in textiles.

References

1. Hossain MA. UV–Visible–NIR Camouflage Textiles with Natural Plant Based Natural Dyes on Natural Fibre against Woodland Combat Background for Defence Protection. Sci Rep. 2023;13(1).
2. Čorak I, Brlek I, Sutlović A, Tarbuk A. Natural Dyeing of Modified Cotton Fabric with Cochineal Dye. Molecules. 2022;27(3).
3. ASTM International. Standard Practice for Computing the Color of Objects by Using the CIE System. West Conshohocken, PA.
4. Goodpaster JV, Liszewski EA. Forensic Analysis of Dyed Textile Fibers. Anal Bioanal Chem. 2009; (August):2009–2018.
5. United States Pharmacopeia and National Formulary. <1061> Color-Instrumental Measurement. Rockville, MD.