I have been asked several times how I clean my shells. So, rather than reply to each comment, I will explain it here. I have only arrived at the method I use by trial and error, with very little research. So keep in mind that you may find something that works better for you, considering what you want to do with your shells.
How I clean my sea shells:
On Sanibel Island it is illegal to take live shells, so cleaning that type is not an issue here.
When I see a nice shell that I want, I look to make sure there is no critter living inside. If there is, put it back. Next, check to see if it has barnacles. If it does have, I usually toss it back unless it is a shell I can’t live without. Removing the barnacles is a difficult and time consuming job. (More on that later.) Sometimes there can be quite a bit of sand hiding inside a shell; I just give it a little swish in the water to rinse out what I can.
A plastic bucket or container filled with a mixture of ¼ bleach and ¾ water, if the shells are not too nasty looking or stinky, works well for me with an overnight soak. Sometimes a stinker (one with maybe a piece of the critter left inside) does turn up, or a shell with the thin brown covering (periostracum) that requires a little more work or scraping. I soak those in a 50/50 mixture overnight and if that doesn’t clean it, I put it in pure bleach for a while. If all of those methods fail, I lay it outside to let the ants, flies, or whatever, clean it. Some of my friends have buried stinky shells and then dug them up after nature cleaned them. Personally a really bad smelling shell doesn’t come along too often and the overnight soak does the trick nearly all the time!
After soaking, I take the shells out of the bleach water and put them in a sink full of hot, soapy water for an hour or so, then rinse them good and lay them out on a towel to dry.
I soak all of my shells in that manner, except shells that have a naturally shiny surface, such as olives, sunray venus, calico clam, etc. Also leave out any fragile shells such as purple tagelus and bubble shells etc. that could be broken. I just do those separately in soapy water and rinse.
If you have shells with barnacles on them, it is sometimes possible to get them off with a dental pick or something of that type. Another way that works well for me, is to use the pointy end of a whelk shell that you don’t mind parting with, to break them loose and scrape off whatever remains. Trying to get that stuff off of a shell is the hardest job ever! I read that the U.S. Navy spends more than $5 million each year researching barnacles, mussels, and various marine slimes because of the strength of their glue. The best super glue, krazy glues or any industrial strength glue we have, can’t work well under water. So, the research is still ongoing. That will explain why I usually drop those shells back on the sand. Sometimes the barnacles happen to be a nice color or just seem to add something to the shell and I just leave them on.
After my shells are completely dry, I put on a thin coat of Cabot Polyurethane Gloss, which is water based and fast drying. I apply it with a tiny brush or (my favorite) a small foam brush. Be careful not to put too much on or it will look milky. I lay them on parchment paper to dry. I use this method because I like a nice shiny finish; the way they look when wet. I’ve also heard of using clear nail polish, but who wants to buy that in large size containers? :-) Some people want to keep the natural look, but still want a little shine. That can be done by rubbing them with mineral oil. I don’t use that method anymore because the dust likes to stick to them too well. (Yes, I do have some dust.) I think that some collectors don’t like to use the poly because they think it devalues the shell. My seashells are for my personal enjoyment, not for resale. They are my ‘Treasures’, after all, and will always be valuable!