As there are two different coatings on this paper sample one would expect two such
optical peaks in the spectrum. Here one has to bear in mind that the penetration
depth of the infra red light in ATR – IR is very limited. This means that the outer
most coating in this case is too thick for the ATR – IR measurement to also see the
inner coating. The paper substrate is only seen in the ATR – IR experiment, because
the coating on the paper is in form of small stripes, which leaves a part of the uncoated
paper visible under the experimental conditions used in this study.