Presented at ASTM D02 Meeting, Phoenix, AZ, June 2018

1. Variable Pathlength Colorimetric
Spectroscopy of Greases
Rich Wurzbach, MRG Labs
York, PA, USA
June 26, 2018

2. Introduction
Grease comes in a wide array of colors
New and In-Service Grease
Methodology introduced in ASTM D7918-15
iLab, Spectroscopy Box, Thin Film Substrate of
grease

3. 3
Wavelength Color
400-465 Violet
465-482 Blue
482-497 Blue-Green
497-530 Green
530-575
Green-
Yellow
575-580 Yellow
580-587
Yellow-
orange
587-598 Orange
598-620 Orange-red
620-700 Red
What is Color

4. 4
CIE Color Space Chromaticity Diagram

5. 5
L*
40
50
60
70
80
90
a*
40
50
60
70
80
90
b*
40
50
60
70
80
90
CIE color space chromaticity diagram
ASTM E308 Defines CIE Color
a* is the change in color in the red spectrum.
a* is positive in the red direction and negative in the
green direction.
b* is the change in color of the yellow spectrum.
b* is positive in the yellow direction and negative in the
blue direction.
L* is the change in shade from white to black.

6. Existing D7918 Optical
Spectroscopy Box

7. Grease Color Examples
Three different
greases
Follows the patterns
identified by the
chromaticity diagram
Colors Sample 1 2 3
Light…dark
L* 48.6 63.5 61.3
Red…green
a* 42.5 13.6 25.8
Yellow…Blue
b* -14.0 -52.1 3.8

8. In-Service Spectrum
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
400
413
426
439
452
465
478
491
504
517
530
543
556
569
582
595
608
621
634
647
660
673
686
699
New Fluid in-service Fluid

9. New Fluid to End of Life
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
400 450 500 550 600 650 700
Wavelength (nm)
Transmission
New Fluid
In-Service Fluid
End of Life Fluid

10. Applications
Greases come in a wide array of colors
Cross contamination, improper fluid and
contaminations can often be seen in spectral
information.
The ingress of metals tend to promote gray
and black colors

11. Limitations of Method in D7918
iLab Spectrometer is called out in method
iLab Spectrometer is no longer manufactured
or supported
A review of 5+ years of testing shows that the
majority of in-service submitted grease
samples are “flatlined” in the visible spectrum
due to excessive absorbance at the 1mm
nominal thickness of die extrusion

12. Improvements to D7918
Introduction of a new spectrometer
Recognition of the limitations of method
due to excessive absorbance
Development of new method to allow
variable pathlength of the grease sample
Allows for a screening process for greases
without requiring die extrusion
High transmittance samples (light, new)
and low transmittance samples (used)

13. iLab following D7918: limited
response, “black grease” #3481

14. Grease under varying conditions
New grease (Vigo)
Significantly dark (3418)
Moderately dark (384)
Slightly dark (389)
Significantly dark (391)

15. #3481: 0.035” path, 0.010” path,
& 0.005” path

16. #391: 0.035” path, 0.010” path,
& 0.005” path

17. #389: 0.035” path, 0.010” path,
& 0.005” path

18. #384: 0.035” path & 0.010” path

19. Proposed Next Steps
Adapt prototype to a standard shim-set for
variable gapping
Upgrade to more robust spectrometer
Utilize disposable rigid window for greater
consistency and elimination of window
degradation
Establish Beta-Test team for testing
existing used grease stream/ILS
Submit research report and ballot revision
to D7918
Acknowledgement: Continued research based on presentation from Dave Wooton, Lisa Williams, Eric
Straub, “Thin Film Colorimetric Spectroscopy of Greases”, STLE, 2010, Las Vegas, NV, USA.