I have been looking endlessly for a solution to the dreaded firestain and firescale so often found on sterling silver. I have decided on using standard sterling and prips flux, however I have not been able to find a definitive explanation of what exactly causes firestain and how the prips flux (or other barrier flux) prevents it.
From what I understand, it has to do with silver absorbing oxygen when hot which then reacts with copper forming a layer of copper oxides, fine silver, firestained sterling and finally sterling silver. Eventually the silver will depletion guild from repeated pickling, however it still absorbs the oxygen making worse and worse firestain even if you don’t see it through the fine silver layer. So it seems it doesn’t matter how clean the surface is because the silver will absorb the oxygen all the same then? However wasn’t the purpose of prips flux to make the surface cleaner (which is firescale not firestain)? so a I am a little confused as it is supposed to reduce the stain not the scale. If anyone could enlighten me on the flux works it would be greatly appreciated.
I bet we would be great friends, because it seems that we both tend to overthink everything to the point of becoming more confused! smile:
Your quote:
“From what I understand, it has to do with silver absorbing oxygen when hot which then reacts with copper forming a layer of copper oxides, fine silver, firestained sterling and finally sterling silver.”
(julie)-----correct-----
“Eventually the silver will depletion guild from repeated pickling, however it still absorbs the oxygen making worse and worse firestain even if you don’t see it through the fine silver layer”.
(julie)-----correct about depletion guilding…although the thicker the layer of fine silver (which has no copper in tt), the farther down the sterling silver layer is (which is the part of the metal that still has copper)…the copper being the part which may interact with the oxygen if the oxygen is able to get absorbed and migrate down to that level…
“So it seems it doesn’t matter how clean the surface is because the silver will absorb the oxygen all the same then? However wasn’t the purpose of prips flux to make the surface cleaner (which is firescale not firestain)?”
(julie)-----the purpose of the BARRIER flux is to create a BARRIER on the surface of the metal, that will prevent/ deter the oxygen from getting absorbed into the sterling silver and reacting with the copper in the alloy, which creates under the surface. The flux does not CLEAN the metal, but rather absorbs the copper oxides that migrate up to the surface of the metal…until it is saturated and unable to absorb more…the benefit of prips flux is that it works longer (absorbs more longer), and at higher tempuratures…
(julie)----- the METAL needs to be clean and free of hand oils, oxides, etc…when applying the flux to the surface of the metal, so that the flux is able to attain FULL coverage of the surface of the metal.
If the metal has oils (ie: from your fingers) or oxides (ie: oxides formed while trying to heat the metal, to properly apply the Barrier flux) then the flux may not be able to attain full coverage on the surface of the metal, in order to protect the metal.
-----(try taking a piece of metal and touching it repeated with oily fingers, and then run water over the surface…the water will probably tend to “ball” up on the surface…(this has to do with surface tension of the liquid…google that and watch youtube videos! fun!)
-----(then, try thoroughly cleaning a piece of metal…I use dish soap, then pumice powder/ water mixed to a paste consistancy…and running water over the surface…the water should “sheet” over the metal…ie: cover the whole piece and not ball up…you may see it pull back from the edge a tiny bit due to surface tension…(i think the TSP in the prips flux helps to break the surface tension(?)…google TSP…saponify…surfactant…surface tension! more fun!)
“so a I am a little confused as it is supposed to reduce the stain not the scale.”
(julie)----- by creating a BARRIER on the surface of the metal. to prevent the oxygen from being absorbed INTO the metal and creating fireSTAIN
Making jewelry should be fun. Go have some fun. Deal with what it gives you. If it is good, great; if it is a challenge, deal with the challenge and when you overcome it, you will have had even more fun. Worrying about the detail is not a bad thing, just don’t let it consume you to where you miss the whole point of making jewelry…Rob
Jumping in kinda late, here. Right now I use copper, before moving to the more expensive silver products. Is fire stain also an issue with copper?
Karen M Brown, Artistic Judaica
Just to give a different perspective, after ten years of casting sterling silver, I have done over ten years of silversmithing in Hatton Garden and much of this has required extensive hard soldering of large joints. Under these circumstances, it is generally accepted in the silversmithing community that you cannot prevent firestain. One remedy obviously is to sand your way through up to 25µ or so of firestain (not at all fun, and can ruin the architecture), or, the commonest response, plate over it.
