Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 1101-1107
Published Online November 2012 (
Characterization and Application of Naturally Occurring
Mineral Based Pigment in Surface Coating
Shweta Umale, Prakash Mahanwar
Department of Polymer and Surface Engineering, Institute of Chemical Technology, Mumbai, India
Received July 8, 2012; revised August 13, 2012; accepted August 27, 2012
New naturally occurring mineral based pigment of general formula Hg2S have been processed and characterized for its
application in surface coating. Various analytical protocol like XRD, FT-IR, SEM and CIE 1976 colour coordinate sys-
tem have been performed for complete analysis of pigment. Characterizations using XRD, and CIE 1976 colour coor-
dinate assessment reveal the formation of pigments displaying colours ranging from brick-red to dark-brown. The typi-
cal designed pigment samples have been evaluated for their mass tone/hiding power, tinting strength and weather resis-
tance by coating on an MS steel panel. Optical, Chemical, Mechanical and performance properties of coating have been
evaluated for its application. The results demonstrated that the dark-brown pigment obtained in the present study was
found to be an interesting alternative to the existing classical toxic inorganic red pigments for surface coating applica-
Keywords: Light Fastness; Colour Value; Surface Coating; Dispersability; Refractive Index
1. Introduction
Natural inorganic pigments have been known since pre-
historic times, for example the drawings in the Pech-
Merle caves in the south of France, Northern Spain, and
Northern Africa were made with charcoal, ochre, man-
ganese brown and clays [1,2]. About 2000 BC, natural
ochre was burnt, sometimes in mixtures with manganese
ores, to produce red, violet, and black pigments for pot-
tery [3]. Arsenic sulphide and Naples yellow (a lead an-
timonate) were the first clear yellow pigments. Ultrama-
rine and artificial lapis lazuli (Egyptian blue and cobalt
aluminium spinel) were the first blue pigments [4].
Cinnabar is red color pigment which can be largely
used in surface coating application but there is large con-
troversy on utilization of mercury containing pigment. But
Mercury in traditional Chinese medicines mainly comes
from cinnabar, deliberately included for therapeutic pur-
poses based on Pharmacopeia of China [5]. Chinese Mi-
nistry of Health has paid close attention to the mercury
contents in traditional Chinese remedies. The allowable
amounts of cinnabar in these preparations have been de-
creased by as much as 65%, from a daily allowable dose
of 0.3 - 1.5 g in the 1977 Pharmacopeia to 0.1 - 0.5 g in
the 2005 Pharmacopeia of China [6], but the mercury in
these traditional medicines can still be thousands-folds
higher than what is considered safe in Western countries
including the USA The analysis showed that cinnabar is
insoluble and poorly absorbed from the gastrointestinal
tract [7-10]. Absorbed mercury from cinnabar is mainly
accumulated in the kidneys, resembling the disposition
pattern of inorganic mercury [11-13].
Use of inorganic pigments are paints, plastics, printing
inks for paper and textiles, leather decoration, building
materials, floor coverings, rubber, cosmetics, ceramic
glazes and enamels. When choosing a pigment for a par-
ticular application, several points normally have to be
considered [14-16]. The coloring properties are important
in determining the application efficiency and hence eco-
nomics. The following properties are also important:
1) General chemical and physical properties: Chemi-
cal composition, moisture and salt content, content of wa-
ter soluble and acid soluble matter, particle size, density
and hardness.
2) Stability properties: Resistance towards light, wea-
ther, heat and chemicals, anticorrosive properties and re-
tention of gloss.
3) Behaviour in binders: Interaction with the binder
properties, Dispersability, compatibility and solidifying
So the main objectives of this study was
1) To process and characterize mineral based pigment
collected from geographical place.
2) To study physico-chemical properties of the pig-
3) To formulate paint by using same pigment and to
study performance properties of the pigment.
Copyright © 2012 SciRes. JMMCE
2. Material and Methods
The material was obtained from various Geographical
places; it is of red colour type (Figure 1). For conveni-
ence red colored sample is referred as (RS). The sample
was crushed by using mortar and pestle and then ground
so as to obtain fine powder. The powder material was
then ball milled to convert into fine powder. Particle size
was determined by using particle size analyzer. Various
analytical protocols have been used for material identifi-
cation such as X-ray diffraction, FT-IR, Scanning elec-
tron microscope (SEM-EDX) and Differential Scanning
colorimetry (DSC). XRD analysis of samples shows the
presence of certain amount of mineral phases. An ele-
mental analysis can be performed by using energy dis-
persive X-ray fluorescence. The physico-chemical pro-
perties were studied.
2.1. Characterization and Testing
2.1.1. Oil Absorption Value (ASTM D 281-31)
Oil absorption value as per ASTM D281-31 was evalu-
ated using alkali linseed oil. Oil absorption value is ex-
pressed as mg of oil/100 gm of pigment. Pigment type,
pigment size, and particle size distribution these are the
factors which affect oil absorption value.
2.1.2. Moisture content of pigment (ASTM D 280-7 5 )
Moisture content refers to the water left in the pigment
after it has dried. Generally, the moisture present account
for a very small fractions and is mainly due to the water
entrapped within different particles of pigment. Here, a
known weight of a pigment is dried in an oven at 105˚C
for 2 hrs. From the loss in weight, the moisture content is
2.1.3. Bleedi ng of Pigme n ts (ASTM D 279-02)
Bleeding is the term used to describe the discoloration or
staining which sometime occurs when a white or light
coloured paint is applied over a deeper colour. Bleeding
property of pigment is evaluated as per ASTM D 279-02.
Pigment is tested for toluene, Xylene, Butanol and MEK.
2.1.4. Hiding Power of Paint (AST M D 344-97)
Hiding power of pigment was evaluated according to
Figure 1. Photographs of red pigment collected from geo-
graphical place.
ASTM D 344-97. Chequers board with alternative black
and white blocks was used for testing. Pigment was dis-
persed in medium and then applied on board. Amount
required to hide the measured space is calculated.
2.1.5. Resistance to Heat (IS: 3493)
Resistance to heat of pigment was evaluated according to
IS 3493. Heat resistance was tested up to 180˚C.
2.1.6. Density (AST M D 1 3)
Specific gravity of pigment was determined according to
ASTM D 13.
2.1.7. Formulation of Paint by Usi ng RS
Paint was formulated by using pigment RS. Various bat-
ches of paint were formulated by varying pigment vo-
lume concentration. Each batch was characterized for its
solid content, drying time, gloss and skinning properties.
The detailed material data sheet is mentioned in Table 1 .
The components of formulation are mentioned in Table 2.
The characterization of each batch is given in Table 3.
2.2. Performance Properties of Coating
Four coating formulation panels (F1, F2 and F3) were
tested for different mechanical and chemical resistance
properties as per the following standard test methods.
The coated panel with formulation is shown in Figure 2.
Table 1. Material data.
Product name Raplakyd-515-60)
% Non- volatile content at 120˚C60 ± 2
Solvent Mineral Turpentine
General ingredient Linseed oil penta
Oil length (%) 64
Acid value (max) (mgs. of
KOH/gm) 10
Dilution solvent % for testing
color & viscosity M.T/50
Color (Gardner) 7
Table 2. Formulation 1.
Raw material Part by wt wt%
Binder (raplakyd-515-60 )12 52
Pigment (RSO) 5 22
Solvent (MTO) 5 22
W & D agent 0.2 8.8
Antisettling agent 0.1 4.4
Drier 0.1 4.4
Copyright © 2012 SciRes. JMMCE
Table. 3 Characterization of batch.
PVC- 15.25
Vehicle non-volatile- 60%
Brushing - Excellent
Levelling- Very good
Settling- Hard
Skinning- High
Gloss- High
Drying time Touch dry—4 - 5 hrs
Hard dry—9 - 10 hrs
Figure 2. Photograph of painted MS panels with pigment.
2.2.1. Sc r atch Hardness
Scratch hardness was carried out as per ASTM D-2197.
The scratch resistance of the samples was determined
using an automatic scratch hardness tester having a hard
end steel hemispherical point of 1 mm diameter as a
scratching needle. The test was moved at a fixed speed of
3 cm/sec beneath the point of scratching needle. The
scratch resistance is reported as the weight on the stylus
to tear off the coating. This test simulates scratching by
sharp objects.
2.2.2. Pe n cil Hardness
Pencil hardness of coating was determined as per ASTM
D 3363 using pencil hardness tester with calibrated set of
drawing leads ranging from B (the softest) to 6H (the
hardest). The process was started with softest pencil to
end with hardest pencil. A scratch hardness value of the
films is equal to the hardness value of the pencil that tear
the film.
2.2.3. Impact Resistance
Tubular impact resistance test was conducted as per
ASTM D2794 to predict the ability of the coating to re-
sist cracking caused by rapid deformation. It is reported
in terms of inch-pound (height-load). Tubular impact re-
sistance test was carried out using an indenter with
hemispherical head of diameter 0.625 inch and 2 lb load.
2.2.4. Flexibility
The Conical Mandrel Bend Test of the coatings was car-
ried out as per ASTM D522. The Mandrel Bend Test is a
measure of flexibility of coating. As applied coat was
dried enough the prepared panels were kept between the
mandrel and draw bar. The lever bar was drawn down at
uniform velocity to bend the specimen approximately of
135˚. The bent surface was observed for crack or other
surface defects.
2.2.5. Cross-Hatch Adhesi on
This test carried out as per ASTM D3359-83. Crosscut
adhesion tape test is used to assess the adhesion of coat-
ing films to metallic substrates. Cuts were made on the
coating in one steady motion with sufficient pressure on
the cutting tool having a cutting edge angle between 15˚
and 30˚. After making two such cuts at 90˚ the grid area
was brushed and a 2.5 cm wide semi-transparent pres-
sure-sensitive adhesive tape was placed over the grid.
After 30 seconds of application, the tape was removed
rapidly and the grid was inspected according to the stan-
dards. The amount of coated area retained under the tape
corresponds to the adhesion efficiency of the coating.
More the coated material removed by the tape, poorer the
adhesion of the coating to the substrate.
2.2.6. L, A, B Values
The L*, a*, b* values of the pigment system were evalu-
ated by using colour Eye 7000 spectrophotometer with
CIELab colour coordinate system.
2.2.7. Chemical Properties
Resistance to acid and alkali was determined by using
ASTM D-4274-88 standard while for detergent resis-
tance standard ASTM D-2248a was followed. For this
test, the coated panels were immersed in 5% solution of
HCL (acid), 5% solution of NaOH (alkali) and 5% solu-
tionof detergent. The immersed panels were maintained
at constant temperature. The panels were removed for
examination after 6, 12, 18 and 24 hours from the start of
the test and observed for loss of adhesion, blistering,
popping or any other deterioration of the film.
2.2.8. So lvent Res istance
The resistance of the coating towards the solvents like
Methyl Ethyl Ketone (MEK) and xylene was determined
as per the procedure given in ASTM D-5402-93. The
coated panels were rubbed with the cotton moist with
respective solvent and observed for any softness of the
film, peeling of the film and loss of gloss.
2.3. Optical Properties
2.3.1. Glos s
Gloss is a measure of ability of coated surface to reflect
Copyright © 2012 SciRes. JMMCE
light at a particular angle without scattering. Gloss was
determined according to ASTM D523-67. Gloss of the
cured sample was measured at angles 45˚ and 60˚ using a
digital mini gloss meter calibrated against internal stan-
dard i.e. refractive index (Komal Scientific Co. Mumbai,
India) and the results are reported in terms of gloss unit
2.3.2. Colour Values
L*, a* and b* values were calculated as per the CIE 1976
method. The L*, a* and b* values of coating were deter-
mined using spectrophotometer. (Gretag Macbeth, Col-
ourEye-7000A, USA). L* determines the lightness or dark-
ness (higher the L* value, higher is the lightness and vice
versa), a* gives the redness or greenness (+ve a* = red-
ness and –ve a* = greenness) and b* indicates the yel-
lowness or blueness (+ve b* = yellowness and –ve b*=
2.3.3. UV Resistan c e
QUV accelerated weathering tester of Q-panel lab prod-
ucts was used for weather ability testing. The panels
were kept in the weathering tester to study the weather-
ing resistance of the coatings. This test is conducted ac-
cording to ASTM G 154. The test was done in two alter-
nate cycles provided with 4 hours of UV radiation and 4
hours of condensation as per the standard. The samples
were tested for the optical properties to observe the
change in colour values. During the accelerated weather-
ing, the surface colour difference of the sample was
measured in order to record photochemical degradation.
The surface colour difference (ΔE*) was measured using
colour spectrophotometer and it was calculated using
CIE L*a*b* system.
ΔL* = Lf
*– Li
Δa* = af
*– ai
Δb* = bf
*– bi
L*, a*and b* represent the lightness, redness and ye-
llowness, respectively.
ΔE* = (ΔL*2 + Δa*2 + Δb*2)1/2
ΔL*, Δa* and Δb* represent the difference between the
initial (i) and present (f) values.
3. Result and Discussion
3.1. Charactrization
3.1.1. XRD Analysi s
XRD pattern of the material shows intense and sharp
peaks which reveal the crystalline nature of pigment Fi-
gure 3. The data obtained from diffract grams was then
analyzed for reflection angle to calculate the interatomic
spacing (D value in Angstrom units). The intensity is
measured to discriminate various D spacing and the re-
sult was compared with standard mineral data to identify
possible matches.
3.1.2. Elemental analysis
Elemental analysis of pigment was performed by induc-
tively coupled plasma—atomic emission spectroscopy
(ICP-AES) and Energy Dispersive X- ray fluorescence
(EDX). Result shows that pigment contain mercury as
major constituent in the form of mercury sulphide.
3.1.3. SEM Analysis of Sample
The morphology of the material was analyzed by using
SEM and were found to be more or less uniform Figure
4. The crystalline nature of pigments has also been no-
ticed from SEM micrograph of pigment. SEM micro-
graph of the sample shows that surface of pigment is
irregular and shows cristae.
3.1.4. FT-IR Spectrum of Pigment
FT-IR spectrum of pigment Figure 5 shows that no
characteristic peak was observed in the spectrum indi-
cating no organic functionality.
Figure 3. XRD pattern of pigment.
Figure 4. SEM micrograph of pigment.
Figure 5. FT-IR spectrum of sample.
Copyright © 2012 SciRes. JMMCE
3.1.5. Physicochemical Properties of Pigments
Physic-chemical properties of the pigment are mentioned
in the following Table 4. Which indicate that pigment
has excellent acid resistance but poor alkali resistance?
The pigments do not show bleeding in organic solvents.
They are neutral in nature. The oil absorption value of
this pigment is in the acceptable range considering the
inorganic nature of pigment.
3.2. Performance Properties of Paint by Red
Colour Pigment
3.2.1. Mechanic al Properties
The results of scratch resistance, pencil hardness, impact
resistance, flexibility, cross hatch adhesion for coating
formulations Figures 1 to 10 are shown in Ta ble 5. From
the table it is clear that impact resistance of paint is good.
The flexibility test was passed for all the pigment coating.
Cross hatch adhesion by tape was determined by apply-
ing cross cuts on the coated panel. All the coating for-
mulations passed across hatch adhesion test. Gloss of lac-
quer coating was compared with gloss of Figures 1 to 3
at 45 and 60. Gloss of formulation 1, 2 and 3 is higher
than lacquer. Result shows that in both the cases gloss
increases after dispersing pigment in lacquer. Improve-
ments in properties are attributed to surface characteris-
tics of pigment.
Table 4. Physico-chemical properties of the pigment.
Parameter Inference
Oil absorption value 29.7 mg/100 g pig.
Particle size 30 - 50 micron
Density 2.66 g/cm3
Chemical nature Neutral
Chemical resistance Acid—good
Bleeding properties
Methyl ethyl ketone—excellent
Table 5. Mechanical properties of pigment.
F1 F2 F3 F4 F5 F6 F7 F8 F9F10
resistance P P P P P P P P P P
Flexibility P P P P P P P P PP
hardness 3B 2B 3B 3B 3B 2B 3B 3B 3B 3B
200 300 300 300 300 300 300 300 300 300
Gloss at
60˚ 78 73 89 71.68 70 71 68 67 6870
Gloss at
45˚ 51 36 45 45 48 52 55 52 51 49
3.2.2. Chemical Resistance
The coating samples were tested for their chemical resis-
tance properties. The results of the tests are shown in
Table 6. Chemical inertness of pigment protects the sur-
face from various chemicals & reagents thereby resulting
in improvement in overall chemical & solvent resistant
properties. It was observed that acid has caused loss in
adhesion resulting in partial peeling off the coating also
alkali causes blistering of paint film. Film shows good
chemical resistance against organic solvents.
3.2.3. Optical Pro perties
The coated panels were tested for the accelerated weath-
ering testing up to 400 hours of exposure. During this
after every 100 hours gloss and colour values of the
tested panels were determined. From the L*, a* and b*
values the discoloration measurement is done by calcu-
lating ΔE* value. Table 7 shows the discoloration value
for the paint coating. We studied change in colour values
with respect to hours exposed for coatings. Result shows
that there is no drastic change in color values after expo-
sure to Quv weatherometer indicating good light fastness.
The color values of natural pigment were compared with
synthetic pigment (red iron oxide) shown in Table 8. A
lower value of DE* i.e., 15.12 indicate that natural pig-
ment has similar mass tone to that of synthetic pigment
and can replace synthetic one.
Table 6. Chemical resistance of coating.
Property F1 F2 F3
Acid Resistance 4 5 5
Alkali Resistance 1 3 3
Distilled water Resis-
tance 1 1 1
Detergent Resistance1 1 1
MEK 1 1 1
Solvent Re-
sistance xylene1 1 1
1Not affected, 2Loss in gloss, 3Blistering, 4Slight loss of adhesion, 5Film
partially removed, 6Film completely removed
Table 7. L*, a* and b* values for paint system during the
accelerated weathering.
S1 S2 S3
*a* b
* L
*a* b
* L
* a
* b
000 hrs40.84 36.06 22.1839.85 25.36 16.55 35.08 19.95 18.86
100 hrs40.76 36.05 22.1839.81 25.32 16.55 35.01 19.87 18.87
200 hrs40.73 36.04 21.1839.80 25.32 16.52 35.01 29.8718.8
300 hrs39.73 36.04 21.1840.20 25.32 16.52 35.01 29.8718.8
400 hrs38.76 36.05 22.1839.81 25.32 16.55 35.01 19.87 18.87
Copyright © 2012 SciRes. JMMCE
3.2.4. Eval ua ti on of Mass To ne/ Hi di ng Power of
The hiding power and tinting strength was evaluated by
coating on an opacity chart at a thickness of 150 μm
(Figure 6). The CIELAB 1976 method of determination
of L*, a* and b* was employed to determine the hiding
power and tinting strength of the colorants by compari-
son of values when coated on a board with a checkered,
white and black background and the results are summa-
rized in Tables 9. The colour difference has been quanti-
fied on the CIELAB based colour difference (DEab),
which is calculated using the Equation (1) [CIE 1986;
CIE 2004; Ohno 2000]. For mass tone, the colour differ-
ence between the black and white region was found to be
DEab = 10.8. A lower value of DEab (3.3) for mass tone
on the black versus the white regions in the case of
Ce0.8Ti0.05Pr0.15O2 sample indicates the ability of the
dark-brown colorant to cover black and white regions
uniformly well.
Figure 6. Photograph of hiding power of natur al pigme nt.
Table 8. Comparison of c olour value of nat ural pigment with
synthetic pigment.
Synthetic pigment Natural pigment
L* 34.10 40.20
a* 23.96 33.47
b* 15.85 25.92
DL* 6.10
Da* 9.50
Db* 10.06
DE* 15.12
Table 9. Colour coordinate of the pigments after hiding
power analysis on white and black surface.
Surface L* a
* b
* DEab
Black 44.1 17.4 17.3 10.5
White 51.6 24.2 21.1 3.4
DEab = [(DL*)2 + (Da*)2 + (Db*)2]1/2
4. Conclusion
Studied natural pigment has good chemical resistance
and excellent mechanical properties. Naturally occurring
pigments shows good performance properties compared
with synthetic pigment, thus natural pigment can be good
alternative for synthetic pigment.
5. Acknowledgements
Author acknowledges to UGC-SAP for providing finan-
cial support and also to sophisticated analytical instru-
ment laboratory (SAIF, IIT. Bombay) for providing SEM
and ICP-AES facility for analysis.
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