Vitamin C serums are extremely expensive and are already rancid by the time you buy them. Yes, the vitamin c has already oxidized and you end up paying for crap. Case in point the cream will look a dark orange or the serum will smell funny and will have a dark orange tinge to it.
Vitamin C is a very volatile substance and cannot last long at all and should be kept refrigerated to maintain its freshness. The BEST way you will benefit from vitamin c is by making the serum yourself, that way you know it's fresh and at it's most potent. Your serum should only be kept for about a week, refrigerated. So it's best to make it in smaller quantities.
Here's what you will need:
L-Ascorbic Acid (powdered vitamin C)
An amber colored .5oz or 1oz glass bottle with a dropper cap
Distilled or spring water
Put 2 tsp water into the bottle, then add 1 tsp vegetable glycerin and then 1/2 tsp of the L-Ascorbic Acid and then shake vigorously. Store in refrigerator for about 7-10 days.
You can buy L-Ascorbic Acid in bulk at your local health food store as well the glycerin.
Until next time, stay beautiful Jacksonville!