Guided Wave Color Measurements (White Paper)
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Measurement of Color
Accurate, Real-time Reliable Color Measurements
Many liquid product speciﬁcations are based on color measurements. Changes in color can be an indicator of ﬁnal product
quality as well as a means to control process variables when
implemented in real-time. Several different color “scales” are
utilized in measuring color in different products or industries.
Some common examples are ASTM color, Saybolt, and APHA
(aka Platinum-Cobalt, or Hazen).
ASTM color (reference ASTM D1500, ASTM D1524) describes
the color measurement method for fuels including lubricating oils, heating oils, diesel fuels, and petroleum waxes. The
color scale ranges from 0.5 to 8. The lowest value of 0.5 being
a light yellow, 2 being yellow, 5 being orange, and 8 being
a deep red. Both of these ASTM methods are off-line manual
Using a Guided Wave color analyzer system to automate the
measurements within a process, eliminates the visual judgement of a technician and delivers online real-time color values
to the process operators that can be used for quality control
or product quality certiﬁcation. Each color measurement is
described here, along with a method summary and suitable
Guided Wave analyzer system conﬁguration (listed in Table 1).
APHA\Pt-Co (Hazen) Color
This test method describes a procedure for the visual measurement of the color of light colored liquids. It can be referred
to by several names: APHA (American Public Health Asociation), Platinum-Cobalt (reference ASTM D1209), or Hazen. The
measurement was originally developed to detect contamination
of water supplies as detected by a slight yellow color. Today
it ﬁnds use in many industries to measure slight yellowness to
determine product quality (either degradation or impurities).
The APHA/Platinum-Cobalt color scale is described in ASTM
D1209 “Standard Test Method for Color of Clear Liquids
(Platinum-Cobalt Scale)”. The ASTM method is an off-line
manual laboratory method. This original test design required an
observer to compare the color of a product to a known
standard, and then judge the “color”.This color scale ranges
from 0 to 500. The lowest value of 0 is referred to as water
white. A value of 500 is distinctly yellow.
Saybolt color (reference ASTM D156, ASTM D6045) is primarily
used in characterizing fuels including automobile and aviation
gasolines, jet fuel, diesel fuel, naphthas, kerosene, lubricating
oils, heating oils, fuel oils and petroleum waxes. Saybolt is a
lighter color range than ASTM. The Saybolt color scale goes from
30, which is considered to be barely perceivable yellow, to –16
which is a deﬁnite yellow. Both of of these ASTM methods are
off-line manual laboratory evalutations. The original test design
required an observer to compare the color of a product to a
known standard, and then judge the “color”.
Measurement of Color
Turbidity (Haze) Color
Turbidity can be used to indicate solid breakthrough in a process. This can be used as an alarm and to invalidate other optical measurments until the problem can be corrected. Turbidity
values can be found in several different units depending on the
application. Two common measurment standards are ASTM
Method D4176 (Haze), and EPA method 180.1 (NTU).
Gardner color (reference ASTM D1544, ASTM D6166) is typically
used in measuring drying oils, varnishes, fatty acids, polymers,
and resins. The Gardner scale is from 1 through 18 with 1 being
a light yellow and 18 being a deep reddish brown. Standards
for Gardner color can be made from metal salts used in the
Platinum∙Cobalt scale (for the lower numbers) and from ferric and cobalt chlorides dissolved in hydrochloric acid (for the
The ASTM method decribes the visual standard for measuring turbidity (caused by immiscible water in fuels) by viewing
cards with black lines of various thicknesses through a 100mm
diameter glass jar of solution. The result is a value (called Haze)
between 1 and 6, with 1 being the clearest.
Haze is typically measured in the reﬁning sector and arises from
water beyond the solubility limit. EPA 180.1 measures light
scatter at 90 degrees in nephelometric turbidity units (NTU).
In this method standards of formazin are available at different
NTU levels to be used for calibration.
The Smart Choice for Reliable Color Measurement
Guided Wave color analyzers are built on the proven multiwavelength ClearView® db technology. This ﬁlter photometer is a dual
beam design that provides increased stability over other single
beam photometers (document #1033). These complete “readyto-go” analytical systems include: 1) the photometer or analyzer,
2) the ﬁber optic cables, 3) the sample interface and 4) the control
software and pre-calibration to the speciﬁc color application.
Another advantage of the ClearView db analyzer platform is that
it is conﬁgurable to many different color scale measurements in
addition to those described here. The two channel ClearView db
analyzer can be conﬁgured for two different color measurements,
such as ASTM and Saybolt, accomplishing both measurements
with one analyzer, simultaneously. Please contact Guided Wave to
discuss your speciﬁc color measurement needs.
Table 1: Color Methods Summary & Analyzer Solutions
0.5 to 7
-16 to 30
1to 6 Haze, NTU 0-1000
Saybolt Analyzer Turbidity Analyzer
30mm Axial Flowcell
(50mm Axial Flowcell
or SST Probe for low
values); Fiber Cables
or SST Probe;
20 or 50mm
Axial Flowcell or
Turbidity Probe or
5mm Flowcell or
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