Check out this spoon scale! It's $20 at Canadian Tire this week, on sale from $50. (It's a Starfrit product!) It's an interesting piece of equipment, and if you are working with volume measurements instead of using weight in your recipes, this is money well invested! You can measure out a liquid or solid ingredient as tablespoons and get a result in grams, which will help you convert your recipes easily! (The white granular stuff in the picture is boric acid.) It also comes with a cup that measures up to 7 tablespoons and 105 ml or more than 1/3 cup but less than 1/2 cup.
What's the big deal with using volume instead of weight anyway? Working with weight is waaaay more accurate, which reduces the potential for failure and exposure to higher than safe or suggested usage rates.
Let's say you make a lotion and use 1 teaspoon emulsifying wax. Are you really using 5 ml of emulsifying wax every time? Let's say you have calculated 1 tsp as being 5% of your recipe (1tsp = 5 ml). This week you might get exactly 1 tsp - next week you might get 1.1 tsp or 0.9 tsp, but it's hard to know you're a little off. The result? Potential lotion fail!
And you really aren't using 5% because 1 ml of emulsifying wax doesn't necessarily weigh 1 gram. Water is 1:1 - 1 ml or 1 cm3 weighs 1 gram - but many things aren't. Oils are lighter than water - 1 ml of oil doesn't weigh 1 gram. (Olive oil is 0.92 g/ml, meaning 1 ml is 0.92 grams.) And each oil has its own specific gravity.
If you create a recipe that has 1 tsp (5 ml) emulsifying wax, 4 tsp of olive oil (20 ml), and 5 tbsp (75 ml) water, how much oil are you using? 20 x 0.92 = 18.4 g or 18.4% by weight. Polawax has a specific gravity of 0.539 g/ml, so 1 ml of Polawax weighs 0.539 grams. 5 ml weighs 2.695 grams, which is no enough to emulsify 18.4 grams of oil! Potential lotion fail!
It's easier to make changes to a recipe when we use weights. You can scale up a recipe easily when we use weight because we just multiply the whole recipe by the desired amount. My recipes are 100 grams: To make a kilogram of lotion, I multiply the recipe by 10. If you do this with volume, think of what kind of difference you'll see! You'll be using 184 grams of olive oil instead of the 20% or 200 grams you want, and 26.95 grams of Polawax instead of the 50 grams we need!
I will be using this helpful device in the near future to show the differences between volume and weight. In the meantime, if you want to know more about weight vs volume, check out the FAQ and read the posts on measuring! Or click on the chemistry section and look for the posts on specific gravity.