This document discusses factors that influence the appearance of paint films such as observing distance, resolution of the human eye, and measurement of gloss and texture. Fine structures below 0.1 mm are difficult to perceive even at close distances. The Wave-Scan method uses a CCD camera to measure "dullness" caused by very fine structures. A structure spectrum analysis allows optimization of paint appearance by examining how baking position, flash-off time, film build, steel quality, and application techniques impact the different wavelength ranges.

1. APPEARANCE OF PAINT
FILMS

2. FACTORS INFLUENCED ON
APPEARANCE

3. APPEARANCE
PERCEPTION

4. APPEARANCE CHANGES WITH OBSERVING
DISTANCE
Below sample having LW = 6 & SW = 17
Visibility of structures is dependent on
the observing distance. The greater the
distance, the smaller objects will appear.
Structures with a size of 10 to 30 mm
can best be seen at a distance of
approx. 3 m. Fine structures in a range
of 0.1 to 1 mm can only be recognized at
a close distance.

5. RESOLUTION OF THE HUMAN EYE
Very fine structures that are below the
human eye's resolution (approx. 0.1 mm)
can no longer be recognized as a light /
dark pattern, even at a close distance. The
result is a reduction of the image forming
quality (IFQ). At 3 m distance, structures
between 1 – 3 mm can hardly be resolved
as a waviness but influence the
appearance. Structures smaller than 0.1
mm influence visual perception, therefore
the wave-scan uses a CCD camera to
measure the diffused light caused by these
fine structures. This parameter is referred
to as "dullness".

6. MEASUREMENT PRINCIPLE: WAVE-SCAN DOI
One manufacturer measures gloss as
percentages (at an unspecified angle)
and gives:
•Flat (1–9% gloss)
•Low Sheen (10–25% gloss)
•Eggshell (26–40% gloss)
•Semi Gloss (41–69% gloss)
•Gloss (70–89% gloss)

7. WAVELENGTH RANGES - SEPARATION INTO 5
RANGES
The waviness of automotive paints is in
a range of approx. 0.1 to 30 mm
wavelength. Orange peel can be seen
on high gloss surfaces as a wavy
pattern of light and dark areas.
The values of dullness and Wa to We form a
"structure spectrum". This allows a detailed
analysis of Orange Peel and its influencing
factors, being material or application
parameters.

8. WHAT IS DOI ?
DOI (Distinctness of Image) can be described with terms like brilliance, sharpness or
clarity. DOI is diminished by very fine structures close to the human eye resolution
(smaller than 0.3 mm)

10. INFLUENCE OF BAKING POSITION ON
APPEARANCE
In general, horizontal
surfaces have shown
better flow and leveling
characteristics, i.e. in the
values for the longer
waves (Wc ... We). The
smaller waves are hardly
influenced by the baking
position.

11. INFLUENCE OF FLASH-OFF TIME ON
APPEARANCE

12. INFLUENCE OF CLEAR COAT FILM BUILD ON
APPEARANCE
The structure spectrum can
help optimize the appearance,
e.g. in determining the
optimum film thickness.
Increasing clear coat thickness
improves flow and leveling.

13. INFLUENCE OF STEEL QUALITY ON FINAL
APPEARANCE
Topcoat on rough steel:
SW dominates visually
Topcoat on smooth steel :
Appears smooth

14. INFLUENCE OF STEEL QUALITY ON FINAL
APPEARANCE
In the following graph, the
substrate roughness telegraphs
through the clear coat and
reduces the brilliance of the
coating. Sample D is a lasertex
panel with a specific texture
resulting in lower SW values.

15. APPEARANCE IMPROVEMENT TECHNIQUES
Original paint with
high waviness
Improvement by
optimized clear
coat application

16. APPEARANCE IMPROVEMENT TECHNIQUES
Improvement by
optimized clear
coat application
Improvement by
sanding of primer

17. APPEARANCE IMPROVEMENT TECHNIQUES
Improvement by
sanding of primer
Improvement by
optimized primer &
topcoat application