Thermographic Imaging of Chemical Contrast via Differential Heating

Latent Heat Thermography is a technique that exploits differences in hydrophobic/ hydrophilic properties on a surface. Our process does not contaminate the sample. The top picture is a visible image taken with a cell phone camera; a 12’’ ruler is in the picture for a size reference. The acrylic fabric has 5 blood stains of varying dilutions on it: the ‘I’ corresponds to neat blood, the ‘X’ corresponds to the 10x diluted blood, the ‘V’ corresponds to 25x diluted blood, the ‘L’ corresponds to 50x diluted blood, and the ’C’ corresponds to 100x diluted blood. The 9 images below the visible are frames from a thermal infrared camera throughout the duration of our process. The camera records at 60 frames per second. The red number corresponds to a frame number. Frame 1 is considered a typical thermographic image. As the Latent Heat Thermographic technique begins in Frame 600, one can instantly begin to see contrast between the bloodstained areas and the neat fabric. 300 frames later, (or 5 seconds), the bloodstained areas are easily distinguishable. You can also see how the ‘V’ stain wicked through the fabric when it was originally deposited. Between Frame 1200 and 1500, the process ends; the post-process portion allows for some different observations to be observed. Evaporative cooling, condensation, and equilibrium processes can be seen in the following frames. These processes are happening simultaneously and lead to the different methods of contrast within each sample.

This technique is not sensitive to only blood, but rather, it is sensitive to different adsorption properties of the sample system. In another test not shown, a piece of metal was smeared with a very thin layer of vacuum grease, which has strong hydrophobic properties. The metal was place against the fabric. The layer was not visible to the eye. During the process, instead of glowing brightly, it was darker than the surrounding areas because of the lack of water adsorption.

Textile industries, forensic labs, museums, industrial processes, artifact preservation, etc.