Here - PMOD/WRC

Results
The gloss standard used in this example is a Byk
Gardner black glass standard of the size 15cm × 15cm.
Investigation of this standard over 8 year shows variation
of about ± 0.5 GLU. If the values have changed polishing
restores the original values within these values. Changes
over the surface also varies about the same amount.
First the gloss standard was measured in a Lambda 900
Perkin Elmer spectrophotometer at 8º near normal
incidence. The beam size was about 1cm × 1cm. An
aluminium mirror with reflectance value 0.8787 ±
0.0035(k=2) at 590 nm and at 8º was used as reference for
the reflectance measurement. Reflectance r = 0.044492 of
the gloss standard was obtained from 12 measurements at
the centre part of the surface with a standard deviation, of
0.000017. From the reflectance measurement the average
refractive index was calculated to be n = 1.5346 ± 0.0010.
The resulting monochromatic reflection r(angleº,n) values
for angles 20º, 60º and 85º were calculated with Fresnel
formula assuming equal size of the s and p components on
the incident light. Results from calculated G, gloss values
for angles 20º, 60º and 85º according to (2), including G lum
with luminous correction(Table 1) and deviation from
earlier calibration are presented in Table 2. The earlier
calibration was done in a goniphotometer setup with a
laser at 633 nm. Correction from wavelength to the
definition and to the luminous G values was done. The
standard deviation of this earlier measurements were in the
order of % and hence the uncertainties are much
improved with measurements in a spectrophotometer.
Table 2: This table presents results of gloss values, G, at 589.26
nm, luminous gloss, G lum , uncertainty and deviation from earlier
calibration, all presented in gloss units (GLU).
Results GLU/20 GLU/60 GLU/85
G 589,26 91.2 94.8 99.5
G lum 91.7 95.1 99.6
U (k=1) 0.45 0.41 0.48
U (k=2) 0.90 0.81 0.96
Earlier cal. 92.2 95.4 99.6
Uncertainty calculation
The uncertainty calculation can be studied in Table 3.
The long time stability of about 0.5 GLU was not used in
the uncertainty calculation. The reflection, r, is the
measurement of the standard reference at 8º . The gloss, G,
is calculated from the r (8º ) via the refractive index and r
(angle). In measurements diffuse scattering and
polarisation effects (Budde , 1979) are estimated to play an
increasing role the larger the angle although the calculation
of r to get G and the luminous correction factor are
estimated to have a minor importance the smaller the
angle.
Table3: In this table the uncertainties are estimated in % of the
measurment value. The uncertainty values in % are used to
calculate the uncertainties in GLU presented in Table 2.
Uncertainty,U
r
(%)
G
(%)
G
(%)
G
(%)
angle 8 20 60 85
Stddev of 0,0017
measurement
Al mirror 0,2
reference uncertainty
Diffuse scattering 0,05 0,1 0,2 0,3
of standard
Polarisation dependant 0,1 0,1 0,2 0,3
uncertainty
Calculation of r to get G 0,3 0,15 0,02
assuming n:+/-0,001
Estimation of 0,3 0,2 0,1
luminous correction
U k=1 0,224 0,490 0,427 0,480
U k=2 0,447 0,980 0,854 0,960
Summary and conclusion
This paper suggests a method of calibration of high
gloss reference standards. The method is based upon a
standard reflectance measurement in a spectrophotometer,
the definition of gloss at n = 1.567 at 589.26 nm
wavelengths to be 100 GLU and from luminous correction
factors deduced by Budde. The uncertainty obtained is in
the order of ± 1 GLU and the obtained gloss values
deviated at the most ± 0.5 GLU from earlier calibration
values. These are the results from first measurements and
further improvements and analysis of the method have to
be done. The the gloss standard long time stability of about
± 0.5 GLU was not used in the uncertainty calculation.
References
Budde, W., Polarization effects in gloss measurements, Applied
Optics 18, 2252, 1979.
Budde, W., The calibration of Gloss Reference standards,
Metrologia 16, 89-93, 1980.
International Standard ISO 2813: Paint and varnishes-
Measurement of specular gloss on non-metallic paint films at
20°, 60° and 85°. 3 rd ed.,1994.
Andor, G., Gonireflectometer-based gloss standard calibration,
Metrologia 40, 97-100, 2003.
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