Thread: Silver Blueing
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Old February 17th 10, 07:00 AM posted to rec.crafts.jewelry
Peter W. Rowe[_2_]
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Posts: 115
Default Silver Blueing

On Tue, 16 Feb 2010 21:13:54 -0800, in rec.crafts.jewelry Jack Schmidling
wrote:

First of all, some comments on the group.

Glad to see a few names here that I recognize from the past. I tend
to hop around from hobby to hobby like a jack in the box and have been
obsessed with amateur radio for the past several years. I have been a
ham since 1955 but out more than in.


The group's gotten slower and slower over the years, as more and more of the
discussion moved to the much busier Orchid mail list, hosted on Ganoksin.com
(where you might wish to also post this question) But I'm still moderating it,
and a few of the other longtime members seem to still chime in when someone has
a question.


I was saddened when I lost usenet access but got to liking Yahoo
Groups a lot. It appears now that Google has enabled an email option
for usenet access but I have not quite figured it out as there is so
little traffic on this list.


If you've got web access, then you have access to this newsgroup through Google
groups. While rec.crafts.jewelry is not a Google group, but rather part of the
older and wider usenet structure, Google includes access to all the text based
usenet groups right alongside their Google-only hosted groups. You can read and
post to the group right from the Google Groups web site. It sometimes is a bit
slower in getting messages to me that are direct news servers, but most of the
time, you won't notice the difference. The Google site also offers a complete
archive of the group, going back pretty much to it's inception, prior to it's
being a moderated group. Or almost that far, I think...


Anyway, thanks for the thoughts on my blueing but I do not think it is
a simple matter of tarnish for the simple reason that it only appears
on the tines. My instinct says that tarnish is a surface phenomenon
and should appear all over the piece.


Yes, but tarnish is the conversion of silver and copper to silver and copper
sulphides (Not oxides, which you have to deal with when heating the metal.
Tarnish normally is sulphides). To a degree, it's influenced by the amount of
copper in the surface, as well as by the amount of copper oxides either present,
or not present, also at the surface and in the surface layers. This brings us
to the subject of fire stain and fire scale in sterling silver. When you heat
sterling in air, without the right flux coating protection, the copper at the
surface immediately oxidizes to the black copper oxide, giving a black surface
(fire scale). This is removed by pickling, leaving a white silver surface which
has little if any copper left, right at the surface. However, at annealing
temperatures, silver is fairly permiable to oxygen, which penetrates a bit into
the surface if it can, depending on lenth of heating and temperature. So under
that thin surface skin of white frosty fine silver, there begins a layer where
oxygen has reached, oxidizing copper that's there, to the red oxide of copper
(the black is two oxygen atoms per copper, while the red is one). This layer
can penetrate some surprising and annoying distance into the surface. Because
there's only 7.5 percent copper in silver, the layer is not red, but rather
faintly pinkish/cream colored. Different, in any case, from clean unoxidized
sterling silver. Ordinarily, it's not noticed much, but when polished, at the
rouge step, clean silver brings up a wonderful deep rich polish, while the areas
with imbedded oxide (this is called fire stain) don't polish quite as well.
Annoying, and it can mess up a finish, so then you have to remove that layer.

Anyway, on your fork, you've got a cast handle. No doubt it got heated some
during working, as well as just being hot during the cool down phase of casting.
If you did little to it beyond lightly finishing it up, as might be the case if
you were trying to retain cast pattern, you might have a surface somewhat
depleted in copper. But if you didn't repeatedly heat that portion while
annealing to forge the fork, and if you also did not protect the tine portion
from fire scale/fire stain formation during annealing, then the tine portion of
the metal may have more imbedded copper oxide, ie a thicker layer of fire stain
within it. And depending on whether you cut the tines last, or before the last
annealing, the inside edges of the cut times, which might have recieved less
filing and sanding than the outer smooth surfaces, might also differ in oxide
content. All these factors will change the way the surface forms tarnish. So
it's quite possilble that only the tines tarnish, if the main portion of the
fork handle has less copper at the surface. Silver itself also forms the
sulphides, but does so much more slowly than does copper, so there can be a
distinct difference in tarnish between copper depleted areas, normal clean
sterling areas, and fire stained areas. \


As the tines are the thinnest part of the piece, I suspect it is a
heat related issue. When tempering during forging, the tines always
got hotter, faster than the rest of the piece and may have left a
latent image of the blue stage on the tines. Why it has just begun to
show up is the real mystery.


Latent image? Blue stage? Ain't rilly no such things. :-) The hotter tines
might have grown a larger crystal structure if over annealed. But annealing and
heating tends to homogeonize the metal structure, except for the bit about
oxygen penetrating as noted above. Oh, and heating to well below annealing temp
(about 700F) for longer times to age harden the metal (which is NOT called
tempering, by the way. Tempering is a process pretty much unique to ferrous
metals) That causes a migration of copper within silver crystals to the crystal
boundaries, which makes the crystal boundaries less flexible, thus hardening the
metal some. The degree to which this works will also be affected by existing
fire stain, as well as by how well and uniformly the metal was annealed prior to
heat treatment. But none of this is "memory" of a blue phase. Blue color,
when there, simply indicates a thickness of an oxide layer. To a degree, this
tells you something about the metal temp, but not much. And there's nothing
about that temp that leaves a blue memory... Which is good. We don't wan't our
silver to be all sad or something from bad blue memories... :-)

By the way, blue itself is an interesting color to see on silver. Tarnish
usually starts as faint to distinct yellowing, going to browns and then quickly
to black. While there can be a peacockpuple//blue color in that range, it's
ephemeral, and hard to actually get or keep when intentionally putting on a
patina... However, the end black color, if you burnish it or rub it, so it's
metallic and shiney, gets a kind of bluish gunmetal grey tone. Very pretty when
intentional. But not really blue. More a bluish black.

My guess as to why it's only just now showing up is that either something in
your water or food has increased in sulphur content (Eating more, or different
types, of eggs?), or equally perhaps, that your original fork had a surface that
was somewhat copper depleted, and now you've worn your way through that layer,
so a difference in tarnishing. Maybe both causes are in play.


I am thinking that somehow annealing it again may be the cure but need
some moral support before venturing back into this.


If this is a surface oxide layer, heating it again and pickling, perhaps several
times, will again deplete the surface of copper, leaving a fine silver thin
surface layer. You have to then not buff it off, as it's thin. Use a fine
brass scratch brush with soapy water to brighten it up again. But this is a
temporary cure, since it will eventually also wear away. And, it anneals the
silver. If before, when you made it, you did not anneal the metal after the
last stage of forging or hammering, then the metal is harder. Annealed, the
fork might be easier to bend... You might also consider simply silver plating
it. Eletroplated silver is pure silver, not sterling, and if well done, the
surface can be somewhat more resistant to tarnish than straight sterling silver.

Or, buy a bottle of tarnex. Pretty aggressive at removing sulphide tarnish from
silver and copper. Thiourea based, stinky stuff. But it works. Then a light
buff to restore the shine if it suffered, since tarnex reduces the sulphide but
doesn't polish. It's a dip. Quick to use.

Or use the free method. Glass or plastic container, or an UNANODIZED aluminum
container. A mix of washing soda (sodium carbonate) and warm water. If the
container is glass or plastic, put a piece of aluminum foil in the bottom. Not
needed for the aluminum container. Soak the silver in this for a while. The
Tarnish will come off. The aluminum sets up an electrolytic cell with the
silver. If no washing soda around, mix baking soda with a bit of salt, and use
that. Quantities not critical Like Tarnex, this removes the discoloration,
but does not repolish the metal. Oh, and the areas between the tines? I'd
guess they get less burnishing/polishing when you clean the fork. So the
surface may be a bit more porous. Use something like the fine brass brush I
mentioned, or even very very fine steel wool, also with soapy water as a lube,
to burnish the metal after it's clean of the discoloration. This compacts the
surface, making it more resistant to re-tarnishing.

Hope that's of use.

Peter Rowe
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