Automobile paint measurements can be performed on a chip of paint using the FTIR transmission method. Automobile paint comprises three layers: final coat, intermediate coat, and undercoat. In practice, each layer is sampled and measured, and the quality of the spectra depends on the sampling method.
If the sample is more than a few millimeters in size, the edge of the sample can be scraped with sandpaper and the microscopic ATR method used to eliminate the troublesome sampling procedure.
The measurement of the three layers in a sanded automobile paint sample by microscopic ATR is introduced below.
The ATR objective prism (made of germanium (Ge)) was pressed against each layer to measure the spectra of the final coat, intermediate coat, and undercoat.
Fig. 2 shows the spectrum of the intermediate coat.

Fig.2 ATR Spectrum of Intermediate Coat

IR Spectrophotometer –– Microscope System

IR Spectrophotometer - Microscope System

The IR spectrum is a pattern based on molecular vibrations that offers information on the sample molecular structure. Combination with an IR microscope permits analysis of microscopic foreign matter down to 10 µm. The infrared microscope is an effective method for the qualification of trace paint samples and for measuring surface deterioration.