Originally Posted by
Labrat81 /img/forum/go_quote.gif Your foundation isn't oxidizing. the pigments used in mineral makeups are metal oxides....titanium dioxide, iron oxides and zinc oxide. These are already oxidized.
Everyones skin is acidic.....the pH of skin is between 4.2 and 5.6.....so this has nothing to do with why your foundation turns orange.
Mineral makeus usually contain no wetting agents (liquids like cyclomethicone, mineral oil, esters, triglycerides...or stuff like sorbitan sesquioleate). Becasue the pigments aren't "wet out" the sebum from your pores, your liquid primer....or even the oils in your moisturizer can intensify the color of the pigments....
Yellow iron oxide is the one that seems to be easier to wet out than the other pigments (this I know from making pigments grinds). So it seems to make sense that it would be the easiest for your sebum to wet out. Your skin doesn't need to be really oily for that to happen...
If you wash your face before you apply the makeup....you are stripping it of most of the sebum. So your face probably has less oil on it when you put your makeup on. Throughout the day your sebaceous glands are pumping out sebum....eventually enough will accumulate on your face and the pigments in your makeup will look more intense.....
Thank you for explaining that so clearly, Labrat81!
I find that as my skin gets oilier in the course of the day, my foundation gets correspondingly darker. The only way to effectively counter that in my case is to use a silicone-based face primer under my makeup. It helps to seal off the skin's surface so that the oils from my pores can't get into my foundation.