This is a spill over post from my post about acne and skin care which you can read about here.
Proper skin care formulations are measured by weight in either grams, ounces or (for really big batches pounds and kilos). If you want to formulate your own products invest in a good scale that can do these functions. I have a regular scale that only measures out to the tenths place (0.1g or oz) and a smaller, more precise scale that can do smaller amounts out to the hundredths (0.12 g or oz)
I write my formulations out in percentages as do most formulators I believe because it is then easier to scale up or down depending on the batch size that is needed. Below is an example of a basic formula.
Phase 1 - Water Phase - Heat to 160F and hold for 20 minutes
Distilled Water 70%
Phase 2 - Oil Phase
Stearic Acid (to make it thicker) 1.5%-3%
Phase 3 - Cool down phase - add these ingredients once your formulation is below whatever the appropriate temp. is for the preservative. In this case it is 122F.
Preservative- Liquid Germall Plus 0.1%-0.5%. I use it at 0.5%
Vitamin E oil 1% (this is an antioxidant, not a preservative)
Essential oil of choice @ 0.5%-1% (for facial formulations I tend to do 0.5%)
In the end your formulation should equal 100%. From there you can decide how many ounces or grams you want to make and multiply it out.
For example if I wanted to make 12 ounces of product I would take each line item and multiply 12 by the percentage of each ingredient listed.
|PHASE ONE - Heat and hold||Batch Size (oz)||Percentage of batch as a decimal||
Final Amount (oz)
|Distilled Water||12oz||x||0.7 (70%)||=||
|PHASE TWO - Oils||
|Oil(s)||12oz||x||0.145 (14.5%)||=||1.74 oz|
|E-Wax||12oz||x||0.03 (3%)||=||0.36 oz|
|Stearic Acid (how thick do you want this to be?) Let's do 2% for today||12oz||x||0.02 (2%)||=||0.24 oz|
|PHASE THREE - Cool Down|
|Vitamin E Oil (antioxidant)||12oz||x||0.01 (1%)||=||0.12 oz|
|Essential oil||12oz||x||0.005 (0.5%)||=||0.06 oz|
|Liquid Germall Plus (preservative)||12oz||x||0.005 (0.5%)||=||0.06 oz|
As you can see in the totals line things aren't adding up. You should always double check your math by adding everything up and adjusting your formula to equal 100% and also ensure that it equals the batch size you intend for it to equal.
The easiest way to correct a formula such as the one listed above it so simply take the excess away from your water amount. If it has very little water or a liquid other than water that needs to be a certain amount then you will have to see where you can make subtractions in order to balance your formula. For today though reduce your water amount to 68.5% and recalculate. You should get 8.22oz and your final formulation should equal 100% and 12 ounces as you intended.
For your oils, if you choose to use more than one you still need to make sure the final amount of oils does not exceed 14.5%. To figure this out take your 12 (the total amount of product you are making) and multiply by 14.5% (0.145), the total is 1.74oz, this is how many ounces total of oils you will have, you can select 2 oils if you want at 50% of that amount for 0.87oz of each oil or you can keep it simple and use one oil at 1.74oz, either way it will be a nice product.
Phase 3 is very important, you MUST properly preserve this formulation. Any product with water in it or one that someone will be using their fingers to take product out of the container OR any product that will be used in an environment that will introduce water (like a sugar scrub in the shower) NEEDS to be preserved. You are making this to help your skin, don't hurt it by leaving the preservative out. If you are unsure or nervous about preservatives, I have other posts about different ones on the site and you can also check with the manufacturer about different ones for different types of formulations.
I am dropping links here for your reference.