What is firescale and why is it our nemesis?!? Firescale, also called fire stain, is the purple discoloration you can see in my sterling silver piece here š More often than not I donāt notice firescale is on my piece when I take it out of the pickle but I see it after I start polishing. A great way to check your work for firescale is to hold it over a white piece of paper it makes it easier to see if your piece is very reflective. So To explain the cause of firescale I have borrowed a few exerts from an article by Charles Lewton-Brain (he explains it better than I can.)- āFire scale is caused by oxygen combining with copper present in the silver-copper alloy. A sterling silver alloy contains 925 parts out of a thousand parts silver and 75 parts out of a thousand parts copper. When the alloy is exposed to oxygen in the air at higher temperatures during annealing or soldering procedures the copper at the surface is converted to Cu2O, cuprous oxide which has a reddish colour to it and then to cupric oxide CuO which is black. It is however not just the metal at the very surface that is affected but deep inside the metal as well.ā That is what annoys me about firescale, it can take a bit of polishing to remove š¬ You can try to avoid firescale by using a protective coating on your work so that oxygen cannot reach the surface during heating. Said protective coatings are usually based on boric acid which is deposited evenly over your work. I have also found Firescoff to work really well as a firescale preventer. Using a charcoal block as your soldering surface is supposed to help as well - āUsing a charcoal block is a way of obtaining a reducing atmosphere-the charcoal present burns forming CO2 and removes oxygen from the vicinity of the metal surface.ā Once you have firescale, how do you get rid of it? The only way I have ever removed fire scale is through sanding and polishing however there are apparently some chemical methods which involve acids and some people also cover it up using ādepletion guildingā techniques or even rhodium plating. If you have info to add to the conversation please jump in! I would love to share more tips about firescale!
