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Figure II.5: Microscopic inspection by a computer microscope

For the first inspection it is very helpful to use a simple mobile microscope (see Figure II.5). These low-cost computer microscopes are easy to transport, easy to use and often deliver surprisingly good pictures that help to improve the sample documentation and support the design of experiment for the next more sophisticated analytical steps. Especially, it is essential when it comes to field investigations at a costumer site or in a production plant. The main task for this inspection is to distinguish easy-to-solve issues from more complex problems. If (for example) a paint chip is sampled from a steel object (machine, steel structure) and the backside of this paint chip exhibits microscopic traces of steel dust or if there are suspicious features of the surface underneath the detached paint like grinding or scratching marks that might hint at a sample pretreatment or drying residues that can point at insufficient cleaning. This information can narrow the scope of the analyses which have to be planned. A paint failure in a multilayer coating system can appear as a bubble of the clear coat upon first microscopic inspection but, in fact, is caused by voids or cracks of the base-material.

This first tool can help to gather more information about the failure but should not be overestimated on the other hand. If e.g. a paint chip disbonds from a clear primer layer because the primer has not been cured sufficiently, the backside of the paint under first inspection with a simple microscope, might exhibit only a very thin layer of the defective primer which is not visible on microscopic inspection. So, this might lead to the wrong decision concerning the path the analysis has to go. Only a surface infrared spectrum of the backside of the paint chip can reveal the true cause of the failure for this specific example.

The first microscopic inspection does not replace a thorough laboratory investigation but can help to avoid wrong approaches to the issue.