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The next step of the analytical process is a personal, visual inspection of the samples. The human visual sense is very sensitive and sometimes realizes details that are hard to measure by machines. It is sometimes quite frustrating to admit that e.g. discolourations are clearly visible but often cannot be detected even by the most sensitive instruments. On the other hand, there are people who call themselves experts and believe that they can classify a failure type just by macroscopic visual inspection. This must be doubted because e.g. a paint bubble of 20 μm diameter in a primer layer of a multicoat system may appear as a crater or a speck in the topcoat upon visual inspection and this is impossible to distinguish without instrumental assistance.

But the watchful eye can find out very important details about the samples which can be precious, when it comes to the evaluation of the analytical data:

 Do the samples comply with the targeted goal of the analyses and the design of experiment?

 How does the failure appear?

 Are the failure spots (e.g. paint specks) randomly distributed or located in specific areas?

 Are there any optical differences between failed parts and sound parts?

 Does the sample exhibit further unusual features which might hint at application failures?

 How many failure spots are noticeable?

 Are all visible failure spots similar or are there different failure types on the same part?

Of course, this list is not comprehensive. Each individual issue requires a customized set of questions. It is good practice that the person who plans the final analytical approach (see Part II Chapter 2.3 “Design of experiment”) should have seen and thoroughly inspected the samples himself before. Please note that touching, wiping, rinsing or other influences on the samples must be avoided during this first inspection, because it can ruin the target area for the analysis.