Jeweller's pickle, also known as jewellery pickle or simply pickle, is a solution used in jewellery making and metalsmithing to remove surface oxidation, fire scale, and other contaminants from metal surfaces. It is an acidic solution that is commonly made from a mixture of water, an acid, and, sometimes, a compound called sodium bisulphate (also known as sodium hydrogen sulphate).
The primary purpose of using jeweller's pickle is to clean metal surfaces and restore their natural shine and lustre. When metals such as silver, copper, or gold are heated during soldering or annealing processes, they can develop a layer of oxidation or fire scale on their surfaces. This discoloration can be stubborn and difficult to remove. However, by immersing the metal in jeweller's pickle, the solution's acidic properties help dissolve and remove the unwanted oxidation.
The acid in jeweller's pickle reacts with the oxides and contaminants on the metal surface. It breaks them down and converts them into soluble compounds, allowing them to be easily rinsed away. The acid in the pickle also helps to remove any residual flux, which is a substance used during soldering to promote the flow of molten solder.
Jeweller's pickle is typically used warm to speed up the reaction, and the metal is usually immersed in the solution for a short period of time, usually a few minutes. After removing the metal from the pickle, it is rinsed thoroughly with water to neutralize any remaining acid and prevent further reaction.
It's important to note that jeweller's pickle is an acidic solution and should be handled with care. It can cause skin irritation and should not come into contact with the eyes or be ingested. It is recommended to use appropriate protective equipment, such as gloves and goggles, when working with pickle.
There are plenty of different acids used by jewellers to pickle their metals.
At NJS we use citric acid. It's a low risk and safe acid to work with and poses very few health and safety risks in its unused powder or liquid form. It works quickly and is cheap and accessible.
MIXING YOUR PICKLE
We mix our pickle at an approximate ratio of 1tbsp of citric acid to 1 litre of water. The precise strength of the solution changes as it is used so you don't need to be exact about this. Always add your acid to the water and not the other way round.
The same solution can be stored used many times and as it is used you'll see it take on a blue colour as it absorbs the copper oxides. We change the pickle in the workshop about once a month but if you're the only jeweller working in your workshop you won't need to change it so frequently.
If the liquid evaporates (carefully) add more water and if it starts to lose it's effectiveness add more citric acid.
When mixing or using your pickle wear eye protection, an apron and take care to not splash or spill the solution. Rinse up any spills quickly with plenty of fresh water.
PICKLE POT
The process happens faster when the solution is warm. You can buy professional pickle warmers which are specifically designed for use in the jewellers workshop. Many jewellers use an electric slow cooker or a baby bottle warmer to heat their pickle. Both work effectively but don't have such longevity as a professional unit and should be regularly check for damage and erosion by the acid.
If you don't have a permanent jewellery space mix your pickle up in a large glass jar (ideally one without a metal lid as this can contaminate your pickle). You can then store the pickle solution safely when you aren't working. When you want to warm your pickle, fill the slow cooker 1/3 to 1/2 full with hot water and place the whole jar into the water - like a bain marie.
You can use your pickle cold but it takes a lot longer. Place pieces into the pickle while they are still hot and check every one - two hours until they are clean.
USING YOUR PICKLE
When you have annealed, soldered or heated a piece and want to remove the oxides, place your piece in the warmed solution and leave until the surface is clean. The amount of time this takes varies depending on the strength and temperature of the pickle and the amount of oxides on the piece. If you are using hot pickle then quench the piece before you pickle it.
Use copper, brass or plastic tongs to take things in and out of the pickle. Steel or iron will contaminate the pickle and cause to leave a plating of copper over everything in it.
When you have removed an item from the pickle, rinse well in plenty of fresh water or water with a pinch of bicarb to help neutralise the acid. Make sure your piece is dry before you continue to work on it. Any traces of acid or water can cause your tools to rust.
DISPOSING OF OLD PICKLE
Although the acid strength of citric acid and most other jewellers pickles is not high enough to dangerous the copper oxides suspended int he used solution are extremely toxic to aquatic life. Used pickle should not be poured down the drain. It will still be extremely toxic even if the acid is neutralised.
If you are able to, leave your pickle in an unlidded container to allow all the water to evaporate. The solid oxides and acid crystals can then be placed in a sealed container and taken to your local waste and recycling facility. Make sure they are clearly labelled so they can be disposed of appropriately.
At the jewellery school we pour our waste pickle into a lidded bucket of clay cat litter. The litter absorbs the liquid making it safer to store in the workshop. The lid has holes so water can evaporate and when it is full we label it clearly and take to the recycling site.
