posted 05-21-2007 01:22 PM            

You can use the search function to find earlier discussions of the phenomenon.

posted 05-29-2007 06:27 PM            

Firstly to understand firescale an understanding of sterling silver (or for that matter any alloy of silver with copper in it) is needed. 925 is parts per 1000 so 7.5% of sterling is usually cooper. When this alloy is in its virginal state it is usually made in an oxygen free environment and this means that a sheet of sterling has a mix of silver and copper molecules evenly throughout.

When the sheet is annealed the first time it will turn black as the copper oxidizes. It is then "pickled" in a 10% solution of sulfuric acid. When removed it is now creamy white. The reason is that the copper oxide has mostly been removed from the surface and now there is a very thin layer of fine (999) silver on the surface and a thicker layer of copper oxide under it. As the sheet is worked and each subsequent annealing and pickling is done the layer of fine silver increases, but only slightly, for 3 or 4 anneals but the layer of copper oxide grows. The approximate thickness of the copper oxide is two thousandths of an inch while the 999 surface is only approx. one thou."

When the piece is to be finished is where the discussion gets tricky...

If no fire is wanted then it can, with difficulty be kept out from the beginning i.e., oxygen free kilns etc. But usually this is beyond the means of most silversmiths except in the big trade shops in recent times.

Next would be the removal of all the offending fire. But this leaves a lifeless cold surface because all hammer marks are removed as well as the "color" because the only way to get rid of it is to file and then polish the work. Also this was not a good option before steam power as polishing by hand was, even in Medieval times, a tedious awful job (in a print of a workshop from 1706 London the youngest apprentice is the one sitting over the basin of water (cold) with the wet brush and pumice... for days?)

So the last option is to leave the hammered surface and the top layer of 999 with the thicker layer of copper oxide.

Since the silver layer is thin and soft it must be handled very gingerly after the final planishing [(the planishing hammer has to have a mirror finish and even dust from over head lights will be seen when planishing) then wood tongs, no knocking it against anything etc.]and then only the gentlest of rouge polishes.

Now the work is sold and from the beginning the top silver layer starts to wear off. After 25 to 100 years depending (and here I am guessing) on how well the original surface was done and how well the piece is handled, not over polished, used roughly, etc. it will start to show the fire. In the beginning it will have small splotches on the high wear areas. Then it will be an even "blue" all over and then the fire itself will start to be polished off and again it will look splotchy. And at last all the fire will be gone and you are back to that original (as in the virgin sheet) mix of silver to copper.

This is a simplified version of affairs because over the ages there have been things done to silver that I am still trying to figure out, such as English shops in the 18th and 19th c using techniques that left a lovely soft white surface with no fire... Or the more modern use of nitric acid to do what is called"bombing" where the fire is very aggressively leeched out. I last saw some one doing it 25 years ago...

Seaduck you might now see which stage your fire is at, coming, or going? I do not think any thing you do will change it except for keeping it freshly polished which is the state that makes it the hardest to see the fire because the copper will oxidize faster than the sterling when it is not polished but will be close in color when it is.

posted 05-29-2007 08:24 PM            

To do this subject full justice, one must discuss oxidizing and reducing furnace environments, full (furnace) annealing versus air-cooling, and other equally arcane minutiae concerning surface treatments.

In short, fire-scale can be prevented or even cured, but treating the disease may kill (or bankrupt) the patient...

posted 05-29-2007 10:06 PM            

Even arts and craft smiths who had the choice let it become part of their style and look. It is hard to imagine an Ashbee or Stone piece without firescale?

posted 05-29-2007 10:27 PM            

The property of silver of absorbing oxygen certainly causes problems if one wants to eliminate fire scale as the copper can and does oxidize deep within the object.

posted 05-30-2007 12:07 PM            

My understanding is that firescale is common on earlier American pieces -- for all the reasons Agleopar describes -- and indeed is sometimes considered a mark of their authenticity. Would you agree with that? Would you say that most of the 'icons' of early American silver do have firescale? Or, put another way, could you reasonably expect to find early American pieces that do not have firescale?

But in any case, I'm concluding that I may be best off putting my wonderful little creamer away...

posted 05-30-2007 02:21 PM            

Modern Arts & Crafts smiths naturally want to show workmanship, and fire-scale, like other metal patinations, are one aspect of that desire. [Even so, how many copper and bronze patinas have been ruined by owners who wanted a bright & shiny look, I wonder?]

However, traditionally fire-scale has been something to avoid and most, if not all, of the processes to do so were developed in the early millennia of metallurgy. I doubt early american smiths were all ignorant of the techniques to avoid fire-scale. I also doubt they felt fire-scale was something to cherish in their work. Most likely, it was simply a lack of resources (time, manpower, money, etc.) which led to the prevalence of the [concealed] defect.

posted 05-30-2007 08:12 PM            

Was there a time period in England or on the continent when fire scale is seen and what do collectors of this silver think of it?

Seaduck thanks for bringing up this topic and is possible to see a photo of your creamer?

posted 05-30-2007 10:57 PM            

Ahwt: I've tried to photograph this piece without much luck; have since acquired a better set-up and will give it a shot but will probably need another lens, too. Not sure you'd be able to see the firescale in any case. But it's a lovely little piece, probably mid 1700s.

I finally read the Lewton-Brain in all its technical glory, and am confused on at least one point. When a dealer was showing me examples of firescale on some early pieces, I thought he said that it typically didn't occur in the areas where soldering had occured, say, where a handle or a lip were attached -- does that seem consistent?