Handheld FTIR analysis for the conservation and restoration of fine art and historical objects

Importance of the topic

Fourier-transform infrared (FTIR) spectroscopy offers a powerful combination of sensitivity, specificity and non-destructive measurement, making it indispensable for the analysis and preservation of art and cultural heritage materials. By characterizing pigments, binders, coatings and degradation products in situ, FTIR supports authenticity verification, condition assessment and informed restoration strategies without harming irreplaceable objects.

Objectives and Overview

This application note illustrates the deployment of handheld FTIR analyzers for on-site examination of diverse historical artifacts. Through multiple case studies, it demonstrates how portable FTIR systems can: identify organic and inorganic compounds, monitor aging and cleaning processes, detect repair materials, assess firing temperatures and evaluate protective coatings under field conditions.

Methodology and Instrumentation

Analyses were performed with Agilent handheld FTIR analyzers (4100 ExoScan and 4200 FlexScan), which deliver benchtop-quality spectra in a compact form. Sampling interfaces included diffuse reflectance and spherical ATR accessories, enabling non-contact or minimal-contact measurements on flat, curved or overhead surfaces. Real-time spectral mapping and an onboard reference library facilitated rapid identification without sample removal.

Major Results and Discussion

Key findings from the case studies include:

• Temple door paints (Beigans Chao-Tian, Taiwan): Diffuse reflectance FTIR differentiated oxalate accumulation, calcium carbonate, talc, kaolin and cellulose in red versus blackened regions, revealing microbial attack patterns without sampling.
• 17th-century painting cleaning: Comparison of spectra before and after mild cleaning showed baseline reduction and removal of silicate signatures from surface dirt, validating the cleaning protocol in real time.
• Glue authentication on pottery shards: ATR spectra distinguished ancient protein-based glues (1500–1700 cm⁻¹ amide bands) from modern synthetic adhesives (strong carbonyl ester bands), confirming the use of animal-bone glue in an Orkney fragment.
• Natural pigment identification: Infrared profiles of Tyrian purple, cochineal carmine, alizarin and indigo showed distinctive bands free of fluorescence interference, enabling straightforward pigment mapping and quantification of pigment loading on stone substrates.
• Firing temperature estimation: Diffuse reflectance spectra of locally sourced clays fired at 200–800 °C exhibited systematic changes in OH vibrational regions. Comparison with an archaeological shard indicated a firing temperature around 500 °C.
• Outdoor mural coating monitoring (“Dr. J” in Philadelphia): Accelerated aging of paint coupons with UV-stabilized polymer coatings was tracked via carbonyl band evolution, establishing a protocol for in situ evaluation of recoating needs.

Benefits and Practical Applications

The handheld FTIR approach delivers:

• Non-destructive, in situ analysis of large or immovable artifacts.
• Rapid screening of multiple areas without sample extraction.
• High-quality spectral data equivalent to lab instruments.
• Real-time mapping to target regions of interest.
• Authentication of repair materials and counterfeit detection.
• Ongoing monitoring of restoration, aging and coating performance.

Future Trends and Applications

Emerging developments poised to enhance in-field FTIR include:

• Integration with hyperspectral imaging and spatial mapping tools.
• Advanced chemometric and AI-driven spectral interpretation.
• Expanded onboard libraries and cloud connectivity for remote collaboration.
• Enhanced detector sensitivity and further miniaturization.
• Augmented-reality interfaces for guided conservation workflows.
• Automated real-time monitoring of environmental and degradation processes.

Conclusion

Handheld FTIR analyzers such as the Agilent 4100 ExoScan and 4200 FlexScan extend the capabilities of conservation scientists by enabling high-quality, non-destructive, on-site chemical analysis. These systems facilitate rapid decision-making, reduce sampling damage and support a wide range of applications from pigment identification to coating performance monitoring.

Instrumentation Used

• Agilent 4100 ExoScan handheld FTIR analyzer
• Agilent 4200 FlexScan handheld FTIR analyzer
• Diffuse Reflectance sampling accessory
• Spherical ATR sampling accessory

References

• Rein A, Higgins F, Leung PT. Handheld FTIR analysis for the conservation and restoration of fine art and historical objects. Agilent Technologies Application Note 5990-8739EN (2015).