244 JOURNAL OF COSMETIC SCIENCE
spreadability (Y2). The obtained data from Table I was used to predict desirability values,
and a response surface analysis was performed.
OPTIMIZATION OF LIQUID FOUNDATION USING MAGNESIUM MYRISTATE
A 32 factorial design was applied (total nine experimental runs) using Design-Expert®
software (13.0.11.0 version, Stat-Ease, Inc., Minnesota, USA). The independent variables
investigated were magnesium myristate (X1) and liquid paraffin (X2), and the dependent
variables were viscosity (Y1) and spreadability (Y2). The obtained data from Table II was
used to predict desirability values, and a response surface analysis was performed.
QUANTITATIVE ASSESSMENT OF RESPONSES FOR VARIABLES.
Viscosity. Viscosity of the formulated product was determined using a Brookfield viscometer
(AMETEK Brookfield, Massachusetts, USA) with spindle number 1 at room temperature
set at 100 rpm. A dial reading in cps was noted for triplicate samples.14
Spreadability. The glass slide method was used to assess the spreadability of the liquid
foundation (in triplicates). A 1 cm diameter circle was drawn in the center of the glass slide
into which 0.5 g of sample was placed. A sandwich configuration was formed by placing
another glass slide over the liquid foundation. The upper plate was loaded with a 25 g
weight for 10 seconds and the increase in diameter was measured. The noted values were
substituted in eq. 7 to calculate spreadability.15
S =Mass Length
Time
× (eq. 7)
PREPARATION OF OPTIMIZED BATCH
Values for calculating sun protection factor (SPF) are shown in Table III. Using optimized
concentration as tabulated in Table IV and Table V, final products F1& F7 were prepared
and evaluated.
Table I
23 Factorial Design of Liquid Foundation Using Conventional Excipients
Independent variables
Levels
Responses
(Dependent variables) Low (−) High (+)
X1: Stearic acid (%w/w) 2 3 Y1: Viscosity
X2: PGM (%w/w) 1 2 Y2: Spreadability
X3: Dimethicone (%w/w) 5 7
Table II
32 Factorial Designs of Liquid Foundation Using Magnesium Myristate
Independent variables
Levels
Responses
(Dependent variables) Low (−) Medium (0) High (+)
X1: Magnesium Myristate (%w/w) 1 2 3 Y1: Viscosity
X2: Liquid paraffin (%w/w) 5 6 7 Y2: Spreadability

245 Magnesium Myristate
Organoleptic test. The external attributes of the formulated product were assessed for its
color, odor, texture, and homogeneity by physical visualization.16
pH. pH was measured (in triplicate) by dissolving an aliquot of formulation in distilled
water (10% w/v).17
Adhesivity test. The adhesivity was measured using a round-scale glass.18 The retention
time of the product on the glass slide was noted in seconds for triplicate samples.
Hedonic test. The hedonic test was used to determine the acceptability and quality of
formulated liquid foundation. Humans subjectively rate the quality of a product in hedonic
tests. As a result, panelists were obligated to provide honest feedback on the product’s
performance.19
Determination of SPF value. The SPF value was determined using an ultraviolet (UV)-visible
spectrophotometer to assess the effectiveness of sun protection. One gram of formulated
foundation was diluted with ethanol to obtain a homogeneous mixture and was then
vigorously agitated to dissolve the components of the liquid foundation. The mixture was
centrifuged at 3,000 rpm for 15 minutes to separate the phases, and the supernatant (top
phase) was collected. The absorbance was measured at wavelengths ranging from 290–
320 nm with an interval of 5 nm. The readings were substituted in eq. 8 to calculate SPF
value of liquid foundation.20
SPF CF I(λ) abs(λ) =∑EE × λ) × × (
320
290
(eq. 8)
Where: CF =correction factor (10), EE(λ) =erythemogenic effect radiation wavelength,
I (λ) =intensity of the sunlight at a given wavelength, and abs(λ) =absorbance of the
solution formulation containing liquid foundation at a given wavelength (λ).
SHORT-TERM STABILITY STUDIES
According to the stability guidelines, the physical and chemical stability of the formulations
were assessed. A plastic container was used to hold the samples. The prepared optimized
Table III
Standard Values of EE(λ). I (λ) Used to Calculate SPF
Wavelength (nm) EE(λ). I (λ)
290 0.0150
295 0.0817
300 0.2874
305 0.3278
310 0.1864
315 0.0837
320 0.0180
Total 1