If you have left your nail polish sitting unused in the bottle for a long period of time, you may have found that is has clumped together and has become so thick you are unable to apply it. Instead of throwing the nail polish away, you can use nail polish thinner. Although you can purchase nail polish thinner at stores, you can make a homemade version as well.
Choose a solvent that you can use for your homemade nail polish thinner. You will only use a single solvent, since mixing them together will prove ineffective. Potential choices include acetone and shellite.
Add some orange oil to the solvent that you have selected to make your homemade nail polish thinner. The orange oil will help make the polish smooth as well as mask the scent of the solvent. Blend equal parts of the solvent and the orange oil.
Consider using nail polish remover as a nail polish thinner. You will just use a smaller amount than another type of solvent. You can also opt to not add the orange oil if you don't have it on hand.
Add a small amount of the mixture to the nail polish. Add only a few drops to start to the bottle of nail polish.
Shake the nail polish bottle well. Remove the brush after at least 10 to 15 minutes and check the consistency. If you need to use more of the solvent, you can add a few more drops and shake it again. Test one nail and allow it to dry before continuing with the rest of your nails.
Remember to dispose of the leftover nail polish thinner after use or store it in a closed container in a cool, dry place away from any potential heat sources since it will be flammable.