|What is it?||Calcium carbonate is a naturally occurring form of calcium—egg shells are made up almost entirely of calcium carbonate!|
|Usage rate||Varies with the end product and the reason for use; 5–30%|
|Texture||Soft, chalky powder|
|Scent||Nothing much—perhaps a bit dusty|
|Solubility||Slightly water soluble|
|Why do we use it in formulations?||Calcium carbonate absorbs oil extremely well, so it can be found in cosmetics and skin care products as an oil control/mattifying ingredient. The high pH of calcium carbonate means you need to be careful with use around the eyes, though.
You’ll also find calcium carbonate in toothpastes as a mild abrasive.
|Do you need it?||No; I tend to prefer silica microspheres, though they are more expensive.|
|Refined or unrefined?||While you can make your own calcium carbonate from eggshells I would recommend purchasing it—the store bought powder is much softer/less gritty than anything you’ll ever be able to make at home.|
|Strengths||Very effective oil absorber/mattifying ingredient, inexpensive.|
|Alternatives & Substitutions||Silica microspheres are a great alternative.|
|How to Work with It||Calcium carbonate can be hot or cold processed. As it is insoluble you can add it to either the heated oil or heated water phase of an emulsion—I’d probably choose the water phase as calcium carbonate is quite absorbent, so it seems wise to put it in the larger phase. In cosmetics, grind it in with everything else.|
|Storage & Shelf Life||Stored somewhere cool, dark, and dry, calcium carbonate should last at least five years.|
|Tips, Tricks, and Quirks||Calcium carbonate occurs naturally in many things, including marble, egg shells, and pearls!|
|Recommended starter amount||30g/1 ounce or less.|
|Where to Buy it||Buy it from an online DIY ingredient supplier or Amazon. It is available as a dietary supplement, and those can be suitable, just make sure what you’re getting is 100% calcium carbonate. Pressed tablets will often have binding ingredients, so look for free flowing powders and read the ingredients list.|