Identifying Metal Surface Stains with FTIR Analysis

Picture this: A manufacturer is preparing a large batch of aluminum sheets for shipment when a sharp-eyed inspector notices faint stains across the surface. The product looks fine at first glance, but in industries like aerospace, automotive, or food packaging, even a small stain can set off alarms. Is it harmless—or a sign of contamination that could compromise performance, safety, or compliance?

This is where Fourier Transform Infrared Spectroscopy (FTIR) comes in.

FTIR allows scientists to go beyond appearances, detecting the chemical fingerprints of residues and contaminants at a molecular level. By identifying the exact cause of a stain, companies can solve the problem quickly, avoid costly rework, and keep production moving.

Why FTIR?

FTIR measures how chemical bonds absorb infrared light at different frequencies, producing a spectrum that acts like a molecular “fingerprint.” This makes it especially effective for identifying organic compounds such as lubricants, oils, or residues that may cause staining on metals.

For manufacturers today, this kind of analysis is more relevant than ever. For example:

• In aerospace, a lubricant stain left unchecked could affect adhesion in coatings or paints—jeopardizing component performance.
• In automotive manufacturing, residues can disrupt welding or bonding processes, leading to costly rework or recalls.
• In food and beverage packaging, surface contamination on aluminum cans could raise both safety concerns and consumer complaints.

That’s why pinpointing the source of stains is not just about keeping materials clean—it’s about protecting product integrity and brand reputation.

The Study: Aluminum Sheets and Lubricant Stains

In this analysis, three pieces of aluminum sheet were tested:

• Two samples with visible stains
• One clean sample (no stain)

The samples had been exposed to a lubricant, and FTIR was used to determine whether the lubricant was the source of the staining. Two approaches were taken:

1. 1. Unextracted Method – Slightly scraping the stain from the aluminum sheet and analyzing the residue directly.
      • FTIR spectra of stained sample one
   2. Extracted Method – Washing the stains with a hexane solution, evaporating the solvent, and analyzing the remaining residue.ResultsUnextracted Samples
      

      

• Lubricant Reference

• Comparison

The stained samples clearly shared chemical signatures with the lubricant.

Key Takeaway

The extracted method proved most effective. By dissolving and isolating the residues from the stains, FTIR provided clearer results that confirmed a connection between the stains and the lubricant.

Why It Matters Today

As manufacturing standards continue to rise, customers and regulators expect defect-free products. A single unexplained stain can lead to scrapped parts, production delays, or warranty claims.

By using FTIR analysis to identify contaminants, companies can:

1. 1. • Reduce waste and costs by addressing the source of contamination quickly.
      • Improve process reliability by confirming whether lubricants, oils, or other residues are to blame.
      • Stay compliant with industry quality standards and customer requirements.

At Innovatech Labs, we use FTIR stain analysis to help clients across industries solve problems just like this—delivering the clarity needed to move forward with confidence.