By Cindy Goldrick
Firescale is the residue layer of oxides that forms on the surface of metal when it’s heated. At high temperatures, oxygen mixes with the copper to form cuprous oxide and then cupric oxide.
Pickle is, at its most basic, a liquid that allows you to quickly and easily remove this oxidation from your metal, especially if you're soldering bezels and need clean metal for further soldering steps.
There are many kinds of pickle. The one you're likely most familiar with is a sulphuric acid that's often sold under the brand-name Sparex. It is a dry acid compound and you use Sparex number 2 for gold, silver and copper. It must be warmed, so get yourself a dedicated crockpot for it and mix ⅛ c Sparex with a cup of water. It lasts for quite a while. Make sure you only use copper tongs in this pickle. If you put steel tweezers into the pickle liquid you will end up copper plating your silver and you'll be very sad. In the metal studio at Beadfx they keep one crockpot for silver and one for copper.
In class I get a lot of questions about when and where to dispose of Sparex pickle. When it starts taking more than five or ten minutes to pickle your metal, and the water turns a lovely shade of blue thanks to all the copper it has absorbed, you have to neutralize it. Wait til it cools, then put it in a container with much more volume than the liquid. Add baking soda and watch the science experiment happen! When it settles, decant it into a jug and dispose of it as you would any hazardous material.
But for those of you who like to work with something a little more gentle on the environment, there are alternatives. Some of them might surprise you with their simplicity, availability and low price tag.
One of my favourite pickles is a simple one and you have the ingredients right in your cupboard: good old white vinegar and salt that does not contain iodine (kosher, sea salt and pickling salt all work.) One teaspoon of salt per cup of water and your work area will smell like a fish and chips shop in no time! This pickle doesn't have to be disposed of in the same way as Sparex. You don't need to neutralize it and I've read that the copper in the liquid can have an interesting effect on the colour of your hydrangeas when you dump the pickle out in the garden by the plant’s roots.
Citric acid pickles are enviro-friendly too. You can buy some specifically created as jewellery pickle. Beadfx carries Nature’s Touch Citric Pickle. A two pound bag sells for around $11. If you're looking for an even lower-cost version though, check out the citric acid at Bulk Barn. Or better yet, get a pack of Kool-Aid out of the cupboard. What's the first ingredient? Yup, ascorbic acid, a type of citric acid. Although I haven't tried it, I suspect if you choose a light colour and pleasant scent like lemon, it would work just fine and bring back some childhood memories while you work. These pickles don't have to be neutralized and are safe to dispose of poured outside into the ground. Google them to confirm mixing proportions for these “home” pickles.
One final thing to mention is that pickle removes firescale but not fire stain, which is embedded deeper in the metal after heating. You often need to undertake further abrasive scrubbing of the metal with steel wool or sandpaper to remove this deeper discolouration. Also, you will likely find that, when you remove your metal from the pickle pot, there is a matte “coating” making it look dull. This too can be removed with abrasive scouring and polishing of the metal to get it back it's shiny, bright state. Happy pickling!