Color measurements
49
NANOCOLOR
®
UV
/
VIS
II and
NANOCOLOR
®
VIS
II V 1.1 / 10.2017
∆𝑌 = −log (
𝑌
100
)
Formula 10
∆𝑍 = −log (
𝑍
188,232
)
Formula 11
The ZERO reference is distilled water.
5.6.6.3
Saybolt color index
The Saybolt color index can be applied to all colorations, ranging from -16 (lightest value) to
+30 (darkest value) and is measured in 50 mm cuvettes. The Saybolt color index is
calculated from CIE L
*
a
*
b
*
values based on the standard ASTM D6045-12 as follows.
𝑆𝑎𝑦𝑏𝑜𝑙𝑡 = 𝛼 + (
𝛽
𝑙𝑜𝑔
10
∆𝐸−𝜃
)
Formula 12
𝛼 = 51,1 𝛽 = 44,5 𝜃 = 2,55
∆𝐸 = √(100 − 𝐿
∗
)
2
+ 𝑎
∗2
+ 𝑏
∗2
Formula 13
The ZERO reference is distilled water.
5.6.6.4
ADMI color index
Similar to the PtCo color scale, the ADMI color index is defined by the coloring of
hexachloroplatinate solutions. It is measured in a 50 mm cuvette. But in order to measure
colorations that are not in the yellow-orange gamut, CIE L*a*b* values are not used for the
calibration, but rather, the
E values of the PtCo solutions are measured against water.
Therefore, a solution with 50 ADMI units exhibits the same
E value as a Hazen/APHA/PtCo
standard solution with 50 mg/L Pt, but it could also be colored red, green or blue. The ADMI
values are not obtained by comparison with the PtCo calibration, but rather, calculated based
on the standard AWWA 2120F through a 4th degree polynomial. The ZERO reference is
distilled water.
5.6.6.5
Yellowness-Index
The yellowness index is calculated from CIE XYZ values. Although it can be calculated for all
colorations, it is defined only for yellow shades. For the yellowness index, the following
formula applies based on the ASTM standard E313-05:
𝑌𝐼 =
100×(𝐶
𝑋
×𝑋−𝐶
𝑍
×𝑍)
𝑌
Formula 14
Pure "white" samples have a YI value of 0. Yellow-red tints produce positive YI values. The
parameters C
X
und C
Z
are dependent on the selected illuminant and the observer. The ZERO
reference is distilled water.
5.6.6.6
Hazen/APHA/PtCo color index
The Hazen / APHA / PtCo color index covers the gamut of colors from colorless (<1) to light
yellow-orange (500). It is defined from solutions of hexachloroplatinate in water containing
hydrochloric acid and is expressed in mg/L Pt. The measurement is made in 50 mm
cuvettes. Photometrically, the platinum-cobalt color index is calculated according to ASTM
D5386-05 from the yellowness index according to ASTM E313-05. The ZERO reference is
distilled water.
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