Start by placing the nail polish mixing balls into the empty polish bottles, then carefully insert a small funnel into the neck of each bottle.
Add your chosen pigments or glitters to the bottles, starting with ¼ teaspoon or less. You can adjust the amount of colorant to change the final look of the nail polish, though I recommend no more than ½ teaspoon of mica per 15ml container.
Once you’re happy with the amount of colorant added, gently tap the bottles and funnels to ensure all of the pigment is in the bottom of each bottle.
Carefully fill the nail polish bottles to the neck with nail polish base, then remove the funnels.
Secure the lids on the nail polish bottles and shake them persistently for at least 60 seconds, or until the color is completely dispersed throughout the base.
Notes
Be sure to check out the step-by-step images above for visual reference.
The nail polish bottles I have linked above come with mixing balls and funnels!
If you are mixing multiple colors of mica powder to create a custom nail polish color, I recommend doing that on a sheet of printer paper before pouring the mica into your polish bottles.
Be sure to use mica powder that is ethically sourced.
Instead of a suspension base, you can use a regular clear base coat polish. Note that you may have to shake the bottle very well before each use as the colorant might settle to the bottom.
Feel free to add cosmetic-grade glitter for an extra sparkle.