Polishing shells

11 March 2024 by Johno

Categories: Opal Treatments | Opal Types

Polishing shells

If you have ever picked up sea shells you will have noticed that many of them have a pearl like appearance beneath their outer coating. When this coating is removed the appearance of the shell is greatly enhanced.

I have been tempted on many occasions to grind this outer coating away using a dremel, but have resisted the temptation because I have read that the dust from the shell is very dangerous if inhaled. It is very similar to silicon dust and can wreck your lungs very quickly. Knowing this has made me very wary .

I knew there had to other ways to remove this coating and just by chance, while reading some old writings,I came across the following article written by someone unknown which sets out the method of doing this and thought I would share it with you.

Polishing Shells article ( As written)

" By this is meant removing the outer coat to expose pearl nacre underneath. As all shells do not possess nacre, it is advisable to ascertain first whether it will improve the shell if you treat it. A nacreous surface is usually indicated in the mouth of the shell or where a portion of the outer surface has been worn away towards the apex.

Shells to be polished should be cleaned of all dirt.Many of the larger,rocky-shore forms have coralline and other growths on them and these can be removed by acid or lime. In the first place , chloride of lime (bleaching powder) is moistened with water into a thin paste, which is brushed over the shell with a small brush. This is left to dry for several hours and should be watched to prevent the action going too far. Some collectors prefer to work only a small area.When the surface is removed, wash the shells in tepid soapy water and thoroughly dry. The pearly nacre will be exposed in a glossy condition.

Alternate acid treatment

If acid is used, it is more efficient if it is used hot.To 4 litres of hot water add 90 grams of hydrochloric or muriatic acid (spirits of salts).  Small shells can be placed in a small net bag and well shaken in it but, in the case of larger ones, the solution should be brushed on with a toothbrush. Some collectors apply the acid neat, dipping the brush in water at frequent intervals and brushing the acid off, working a small area at a time.The chief points to remember are to watch the action of the acid or lime to ensure it doesn't go too far and to exercise great care in the handling of either agency. Remember the acid,or lime will attack the surface structure of shells and will destroy their scientific value and also your hands if you allow either to get on them. Wear gloves and safety glasses to prevent any damage to you .

Use of emery paper on some shells.

Emery paper can be used to remove coats from certain shells such as common mussel. Commence with a coarse paper, using finer paper as you get closer to the nacre. Some shells such as Cowries, are naturally polished, but after being kept in a collection for some years they may become dulled with grime. This grime can be removed by gently rubbing with fine steel wool. The natural polish of shells can be emphasised by wiping with a few drops of boiled linseed oil or machine oil on cotton wool.This helps  to preserve all sea shells, except those with hairy epidermis and if it is desired to keep this fresh, a slight smearing with petroleum jelly will prevent it from drying or cracking."


I have to admit I haven't tried these procedures myself and would love to hear from anyone who does to let us know if they are successful.

Please be very careful when using bleach or acid.These chemicals give off fumes so should only be used outside and with the user using gloves, safety glasses and a mask. Also remember that if you use a toothbrush it can cause splatter and these chemicals will burn you or rot clothing very quickly.

Also never add water to acid. It will splatter and cause heat and fumes and is very dangerous.

Hope these notes help.


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