HOW DO I READ A RECIPE?
Just about every recipe on this site is done in weighted measurements. (Mineral make-up is an exception because I might be dealing with tiny tiny amounts and my scales aren't that great! I am working on changing those recipes!)) And when you visit a supplier's or manufacturer's sites or get textbooks on cosmetic chemistry, it is all done this way. A recipe should total 100%.
As an aside, when you see something that says "water q.s", it means add enough water to make the recipe total 100%.
When you see a recipe in percentages, switch the % sign for the word grams. Do not switch the % for ml or liquid ounces or anything to do with volume. This is all about weight.
For those of you using ounces, do you not switch the % for weighted ounces. You will make 100 ounces by weight, which is freakin' huge! 6.25 pounds of product! Massive! And the math is annoying. If your scale can do grams, use grams. Please!
PRETEND RECIPE - do not make this as it isn't workable!
10% aloe vera
10% chamomile hydrosol
10% cocamidopropyl betaine
10% olive oil
10% rice bran oil
8% shea butter
10% cetyl alcohol
1% essential oil
Convert the % sign for each ingredient into the word grams, and you will have a 100 gram or about 3.5 ounces by weight of product. It's hard to predict the volume of the recipe - is it 1/4 cup or 3/8 cup? - but it's easy to know the final weight because it should add up to 100 grams.
If you want to make more of a product - and I don't recommend making more than a double or triple batch the first time you make something - substitute the % sign for the word grams, then multiply the ingredients by 2 or 3 or whatever amount you want.
10% aloe vera becomes 10 grams aloe vera, which becomes 30 grams aloe vera if I want to make a triple batch.
10% cetyl alcohol becomes 10 grams cetyl alcohol, which becomes 30 grams cetyl alcohol if I want a triple batch.
1% preservative becomes 1 gram preservative, which becomes 3 grams preservative if I want a triple batch.
And so on...
Because it's more accurate and easier to use when we want to get into larger batches.
Let's say we get into our workshop today and we use 2 tsp Polawax in the recipe above (2 tsp = 10 ml). We love the lotion and make the same amount again next week. But it fails! Hmm...but we love it so much and it worked once, so let's make it for Christmas. We want to make at least 15 - 4 ounce bottles. So we figure we need 2 tsp x 15 emulsifying wax in this product. (30 tsp = 150 ml). The lotion fails again. Why?
Two reasons...The first is that you might not have used 150 ml emulsifying wax. You might have added more or less because it's not that easy to use measuring cups. Is it a level cup or a packed cup or a melted cup? There are just too many ways to mess up this kind of measurement. And you definitely didn't use 10% as required by the recipe.
But wait - I used 10% by volume. But our recipes are meant to be created by using weighted measurements. You didn't use 10% by weight. Why is that? Specific gravity! Specific gravity "is the ratio of the density of a substance to the density (mass of the same unit volume) of a reference substance." (Wikipedia)
This means that when we compare our ingredient to a similar amount of water, we'll come up with a number. If we have 1 ml of water, it weights 1 gram. Everything is compared to this. Water has a specific gravity of 1. If my aloe vera liquid has a specific gravity of 1, this means that 1 ml aloe vera weighs 1 gram. If my rosemary hydrosol has a specific gravity of 1, this means that 1 ml rosemary hydrosol weighs 1 gram. And so on.
specific gravity of 0.916 to 0.921 grams per millilitre. So let's say we want 10% rice bran oil in our product. If we use 10 ml or 2 tsp, we would actually have 9.16 grams of rice bran oil in our product. If we use 60 ml or 1/4 cup of rice bran oil in our product, we'd have 54.96 or 55 grams in our product, not 60 grams. And when we get to using larger amounts, 500 ml of rice bran oil isn't going to be 500 grams but 458 grams. We'll be using much less than we wanted!
Polawax has a specific gravity of about 0.8, meaning 1 ml weighs 0.8 grams. If we use volume measurements we'd end up having 8 grams Polawax instead of 10 grams. Too little emulsifier means the lotion fails. As well, this product is a solid - it comes in pellets. But it comes in pellets. Do we melt it before or after the volume measurement? If we use weighted measurements, we know we're using the same amount every time.
What if we wanted to add lactic acid at 10% to a recipe? If we add 10 ml (2 tsp) to the recipe above, have we added 10%? It has a specific gravity of 1.2, which means that 1 ml will weigh 1.2 grams. 10 ml would weigh 12 grams, which means we'd have 12% lactic acid by weight in the recipe! If the safe as used amount for lactic acid is 10% in a product, we've could be putting our skin at risk.
Or look at sodium lactate with a specific gravity of 1.32. The safe usage rate is no more than 3%. Going over that amount can result in sun sensitivity. If you used 3 ml (3/5 tsp) in a product, we'd have almost 4 grams going into the product. Too much!
As you can see, volume and weight measurements are not equal. Using volume measurements means that you aren't following the recipe correctly and things might fail or the consistency isn't right or you are going over suggested safe usage rates.
Plus, you always leave something behind in the measuring cup or spoon when we're done!
Why? Let's say you make a 4 ounce bottle of something with 20 drops essential oil, but you want to make 15 bottles for Christmas. Do you want to stand there and add 300 drops of something?
And besides, what happens if you use 21 drops or 19 drops? I haven't found an essential oil that is so potent that you need to use teeny tiny amounts like drops. Can our essential oils enthusiasts chime in here as I'd love to learn more!
emulsion - heat, mixing, and emulsifiers. Sometimes we can heat something and mix it so well that it will work for a short period of time. If you make a lotion today and use it all up by next weekend, it might not have failed in that period of time. Give it ten days or ten weeks and it probably will.
This is one of the reasons I get upset when I see people selling products shortly after learning to make them! You need to take the time to watch how the product changes over time. (Click here for the post Give it time!)