Seashells can be used as accessories in your home, but they must be cleaned properly first.
You must remove all sand, dirt, and other yucky stuff before putting them on display.
Here are the steps for how to clean and polish seashells.
In order to clean your seashells, remove the majority of the dirt and debris by simply wiping it off with a paper towel or dish towel.
Before wiping them clean, you might want to rinse them with your garden hose or put them in a bucket of water and dump the out water, repeating the process several times.
Try to remove as much sand and debris before bringing them into your home.
Use a toothbrush to scrub any visible dirt off of your seashells. Don't forget to clean the inside of the seashells also.
If the previous owner of the shell's body is still inside the shell, it must be removed else it will stink really bad. You can use tweezers to remove things, or use tweezers in conjunction with one of the methods listed below.
1) Bury the seashell in your yard at least 12" down and leave it there to decompose for at least 1 month.
2) Put the seashells in a pot covered with room temperature water and bring it to almost a boil then shut off the heat and let it sit until it reaches room temperature again. This should free anything left inside, however not all shells respond well to water that hot.
3) You can put your seashells in a plastic bag, put water in the bag to cover the seashells, then put them in the freezer. After they have frozen completely, defrost them and anything inside should be able to be removed easily.
To ensure that the seashells are free of germs and yucky stuff, soak them in a cleaning solution of water with 10% chlorine bleach.
Make sure the water and bleach solution completely covers the seashells.
Take proper precautions when using bleach that you do not splash it on anything that might be affected (such as your clothes).
After about an hour, remove the seashells from the bleach and water and rinse them thoroughly (several times) with clean water. Allow them to dry.
If you want your seashells to look white (or whiter than they currently are), soak them in a solution of 50% water to 50% bleach and soak them for a longer period of time.
Mineral Oil or Baby Oil
To make your seashells shine for a polished look, rub them with mineral oil or baby oil and allow that to dry for 24 hours.
If you want to use polyurethane on your seashells for added polish, skip the oil step and spray them with aerosol polyurethane instead. Make sure to do this in a well ventilated area.
You will most likely need to wait for one coat to dry (per the time listed in the manufacturer's instructions) then flip the seashells over and spray the other side.
Each side may need two coats or more for a nicely polished look.