How to Clean Shark Teeth, Fossils and Sea Glass (Hint: Mostly No Acid)
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Shell season usually comes with a side haul: a handful of fossil shark teeth, a fossil shell or two, and a pocket of sea glass. It's tempting to put everything through the same cleaning routine. Don't. Shark teeth, fossils and sea glass are made of different materials than seashells, and acid, the go-to for crusty shells, is the wrong tool for most of them.
Here's what each one is made of, what to use, and the few cases where a short acid dip makes sense. For seashells themselves, start with How to Clean Seashells Safely.
Fossil shark teeth: skip the acid
Most shark teeth found on beaches are fossils. Over thousands to millions of years, minerals from the surrounding sediment replaced or filled the original tooth material, which is why they turn black, gray, brown or tan instead of staying white. Tooth material is built on a calcium phosphate mineral (apatite), not calcium carbonate, but acids can still attack it, especially the thin, shiny enameloid on the blade and the more porous root.
Our recommendation: don't use acid on shark teeth. You risk dulling the shine, etching serrations, weakening or cracking the root, and changing the natural color that collectors value.
What to do instead:
- Soak in fresh water for a day or so, changing the water, to draw out salt. Salt left in a porous fossil can crystallize as it dries and cause flaking over time.
- Brush gently with a soft toothbrush. Work sand out of the root with a wooden toothpick.
- Dry slowly at room temperature, out of direct sun and away from heaters.
- Leave them natural. Many collectors avoid bleach, oils and coatings on fossil teeth. If you want to try a finish, ask a local fossil club first and test it on a common tooth.
Rare or valuable teeth, like a large megalodon tooth, are worth showing to a fossil club or a professional preparator before you do anything beyond water and a soft brush.
Other fossils: acid often dissolves the fossil itself
Fossil shells, corals, sand dollars and many other invertebrate fossils are often still made of calcium carbonate, either the original shell mineral or calcite that replaced it. To an acid, a fossil scallop and a barnacle look the same. Dip a fossil shell to remove the rock around it and you may dissolve the fossil's surface detail first.
Our recommendation: don't acid-clean fossils at home.
- Soak in fresh water and brush with a soft brush.
- Use a pick or dental tool under good light, or a magnifier, to remove loose matrix a little at a time.
- Stop while there's still a thin layer of matrix left if the fossil surface is fragile. A little rock is better than a broken fossil.
Professional preparators do sometimes use carefully controlled acid baths, but only when the fossil and the surrounding rock are chemically different, for example a fossil that has been replaced by silica sitting in limestone. Identifying that takes expertise, and it isn't a beach-bucket project.
Also check collecting rules before you dig. Rules for fossils, especially vertebrate fossils, vary by state, park and land owner, and some require permits.
Safety box: chemical-resistant gloves and eye protection are required. Safe-HCL is a modified acid that is non-corrosive to skin, unlike muriatic acid, but it is still an acid. It may irritate skin, it causes serious eye irritation, and its vapors are harmful if inhaled. Wear chemical-resistant gloves and safety glasses or goggles every time, work outdoors or in a well-ventilated area, always add acid to water, and never mix acid with bleach. Read the Safety Data Sheet before you start, and keep children and pets away from your work area.
Sea glass: acid isn't needed for the glass, but it can lift crust
Sea glass is glass, mostly silica, and glass stands up to hydrochloric-type acids far better than shell or fossil does. The frosted surface you love comes from years of tumbling and slow chemical weathering. A short acid dip won't create that frost, and it won't remove it either.
Most sea glass needs nothing more than:
- A soak in warm water with a drop of dish soap.
- A gentle scrub with a soft toothbrush.
- A rinse and air-dry.
Where acid can help: sometimes a piece comes home with barnacle bases, worm tubes or white calcium spots stuck to it. Those are calcium carbonate, so a short, diluted dip can soften them. Wear chemical-resistant gloves and safety glasses, work outdoors or somewhere well ventilated, use 1 part Safe-HCL to 2 parts water (always add acid to water), dip briefly, pick, then neutralize in baking soda water and rinse. Test one piece first.
Keep these out of the acid:
- Beach pottery and china shards. Old glazes and decorations can be damaged by acid, and some older glazes contain lead, which acids can draw out. Use soap and water only.
- Glass with paint, enamel, gilding or labels. Acid can lift decoration.
- Anything you think might not be glass, like beach stones, shell fragments mixed in with glass, or plastic "sea glass."
One more note: some glass sold as sea glass is artificially frosted with etching products. Real sea glass gets its frost from the sea, not from a bottle. If a piece looks perfectly, uniformly frosted, it may be machine-tumbled or etched.
Quick reference
| Find | Acid? | Clean with |
|---|---|---|
| Fossil shark teeth | No | Fresh-water soak, soft brush, toothpick, slow dry |
| Fossil shells, corals, invertebrates | No | Water, soft brush, pick under magnification |
| Sea glass | Usually not needed; short diluted dip only for barnacles or calcium spots | Soapy water, soft brush |
| Beach pottery, decorated glass | No | Soapy water, soft brush |
| Sturdy crusty seashells | Yes, short diluted dips | See our crust removal guide |
For the crusty shells in your bucket. Keep the teeth and fossils on the water-and-brush side of the table. For the barnacle-covered whelks and clams, the Safe-HCL Seashell Cleaning Kit includes a quart of Safe-HCL, a 1-gallon HDPE jug with lid, tongs, a stainless pick set (handy for fossil matrix too), a scrub brush, and the nitrile gloves and safety glasses you need to wear.
Not sure whether a shell can take acid? Read Shells You Should Never Acid-Clean before you dip.
WARNING (SDS): May be corrosive to metals. Harmful if inhaled. Causes serious eye irritation. Wear eye protection and chemical-resistant gloves; use outdoors or in a well-ventilated area. Avoid breathing mist, vapours, or spray. Keep only in original / HDPE packaging. See Safety Data Sheet before use. Always add acid to water. Neutralize spent solution per SDS / local rules.