I have bought a colour changing lipstick with the colour Phloxine B.(Other ingredients, see below...) Normally this colour changes to pink at pH 5. So this means on skin it changes its colour because the human lips have a pH about pH 5-6.
I have made a test: I cut pieces of the lipstick and inserted them into a solution of HCl (no colour change), dest. water (pH7) (no colour change) and a solution of NaOH (colour change!)
My question is: Why doesn't it change its colour in water?
Ideas so far:
due to the solubility of the liphophile lipstick and the surface tension of water, there is no real contact between water and the lipstick possible and therefore also no reaction
the citric acid that is an ingredient of the lipstick solves in the water so the water gets acid and there is no rise of the pH value
the reaction between water and the lipstick is not possible because water doesn't have enough OH- -Ions (but why does skin have those ions?!)
On top of that i made a few more tests: The lipstick changes colours when spreaded on: tables, paper, skin, plastic-lids
it doesn't change colours on: metall, glass, porcelain, plastic with a very plain surface.
Can you please help me out?
Ingredients: polyisobutene, caprylic/capric triglyceride, cera microcristallina (microcrystalline wax), euphorbia cerifera (candelilla) wax, prunus amygdalus dulcis (sweet almond) oil, cannabis sativa (hemp) seed oil, menthol, tocopheryl acetate, glycine soja (soybean) oil, tocopherol, caprylyl glycol, ethylhexyl palmitate, glycerin, caprylhydroxamic acid, beta-sitosterol, squalene, ricinus communis (castor) seed oil, ethoxydiglycol, citric acid, CI 19140 (yellow 5 lake), CI 45410 (red 27 lake), CI 61565 (green 6).