Was: Maximum number of annealing cycles
I am curious as to where the term raising the fine silver came from.
Is silver levitation going on?
Hello Roger,
A better term might be lowering copper ;-). By sequentially heating
and pickling, the copper in the alloy is gradually removed, leaving
the silver on the surface of the metal.
Judy in Kansas, where the recent frost did toast the tender plants
left uncovered. Hoping that a few warm days will restore the peppers
and yield a decent harvest.
I, too, never cared for the term “raising the fine silver.” You’re
not raising the silver, you’re removing other metals from the top few
thousands of an inch.
There should be standard terms. How about the following:
For silver: Depletion silvering
As in:
I’m depletion silvering the surface.
I depletion silvered the surface.
The surface is depletion silvered.
For gold: Depletion gilding
I’m depletion gilding the surface.
I depletion gilded the surface.
The surface is depletion gilded.
Other suggestions?
Jeff Herman
I am curious as to where the term raising the fine silver came from. Is silver levitation going on?
There is no levitation going on. It is simply a matter of heating the
silver copper alloy without flux so that the copper at the surface is
oxidised but not so long for firescale to develop below the surface.
Silver is much more resistant to oxidation. The piece is then
pickled, normally in sulphuric acid or sodium bisulphate, to dissolve
the oxides of copper and leave behind a higher concentration of
silver at the surface. If this process is repeated then you gradually
develop a layer of somewhat porous pure silver at the surface which
can be made less porous by brushing with a brass scratch brush with
water and detergent. I typically repeat the process several times to
develop a thin layer of pure silver at the surface. This makes the
surface of the piece more resistant to tarnish because tarnish is
mostly affects copper.
I particularly use the process when I want to use a reticulated
finish on the piece. This can work with.925 silver but works better
with a.825 alloy. You can make this by melting together.925 silver
and an 10% copper. In this case I typically use 9 to 12 oxidation
and pickling cycles. This results in a somewhat thicker skin of pure
silver and a.825 core. This produces a piece where the melting point
of the surface layer is about 100C hotter than internal core so that
when you CAREFULLY heat the piece on a ceramic or charcoal block you
can bring it to a point where the core is molten and the surface is
slushy. You can then play the torch over the surface to texture the
surface in ripples and wrinkles. It is a chancy process with rather
unpredictable results that is cruising on the edge of turning your
piece into a puddle. This technique is called reticulation and was
apparently first developed by Fabege in the early 20th century. It
was only a technique available to jewellers when we started using
gas torches for soldering.
All the best
Jen
Depletion gilding is probably the term you’re discussing- even
though a layer of fine silver rises to the surface through a
crystallographic reaction ( more like recombination) one buries the
copper in sterling.Trick is, if there is a further operation that
involves heating the metal once, twice or more if it’s a complex
piece you need to solder together, the likelihood the copper will
show up again as oxide is great if you don’t apply a skin of a
product like Cupronil or layer an alcohol boric acid solution on the
metal by warming ( not heating to the degree you would need to, to
depletion gild the surface) the piece. All said, I always buy fine
silver casting grain, or other mill products to avoid the problems
inherent in sterling.If i am reclaiming scrap silver I use a scale
and add germanium to the crucible to roll out an “argentium” type
alloy…It’s easier to keep separate crucibles for different metals
than to keep a lot of silver mill products ( except for tubing which
i keep a fair amount of different gauges and thicknesses on hand as
milling one’s own is a time consumer- I occasionally will use a
drawplate -( and have been known to use a screw gauge as well !) if I
need an odd size or If I am making a tube setting quickly- if the.999
Ag is annealed and the plate is well lubricated with a stick or paste
type lube it is fast work particularly for the odd large round
faceted stone or cab… I mill most of my own gold and silver products
so for karating and colouring fine silver casting grain is the most
versatile silver to keep on hand as with the right tools( combination
rolling mill, machined moulds for pouring sizing wires or odd shaped
stock, forming stakes and bezel punches, and sharp shears) one can
make exactly what is necessary without tying up money in having a lot
of stock sitting around…rer
My only problem with this term, Jeff, is that to me it sounds more
like you are depleting the amount of silver (rather than "raising"
it.
Margaret Malm
Depletion gilding is probably the term you're discussing-
Its not gold so it is not depletion gilding.
even though a layer of fine silver rises to the surface through a crystallographic reaction ( more like recombination) one buries the copper in sterling.
The silver does not go anywhere and the copper does not get buried
and it is not a crystallographic reaction.
Coper is oxidized by heating in the presence of air, copper oxides
are soluble in an acid aka pickle, copper oxides dissolved silver
left behind.
James Binnion
James Binnion Metal Arts
I do depletion guilding of sterling silver to raise the layer of
fine silver so I may enamel the surface.
Jennifer friedman
My only problem with this term, Jeff, is that to me it sounds more like you are depleting the amount of silver (rather than "raising" it.
From http://www.ganoksin.com/gnkurl/ep7zn2 (PDF file)
"Depletion gilding is a process of heating sterling silver
sufficiently to oxidize the copper in the surface layer of the
alloy and then removing that oxidized copper layer by soaking in
a mild acid solution (the "depletion"). This process leaves a
thin layer of fine silver on the surface of the metal (the
"gilding")." So you are depleting the copper, not the silver. I
have heard it called "raising the fine silver" more often than
"depletion guilding".
Richard Hart G.G.
Denver, Co.
Hello Margaret,
Funny, I feel the opposite. You’ll notice that I never said
“depleting the silver.”
I'm depletion silvering the surface. I depletion silvered the surface. The surface is depletion silvered.
The term “depletion gilding” has been around forever. Why not apply
the same terminology for silver? As I mentioned, you’re not
“raising” the fine silver, you’re actually removing those metals that
decrease its purity.
Jeff Herman
I believe the traditional term for “depletion silvering” (as opposed
to depletion gilding) is ‘blanching’.
Janet in Jerusalem
Depletion gilding is a process of heating sterling silver sufficiently to oxidize the copper in the surface layer of the alloy and then removing that oxidized copper layer by soaking in a mild acid solution (the "depletion").
If you are talking about silver it is not gilding. If you refer to
gilding silver you are talking about gold plating or otherwise
covering silver with gold.
Definition:
“The term gilding covers a number of decorative techniques for
applying fine gold leaf or powder to solid surfaces such as wood,
stone, or metal to give a thin coating of gold.”
- The art or process of applying gilt to a surface.
- Gold leaf or a paint containing or simulating gold; gilt.
James Binnion
James Binnion Metal Arts
I do depletion guilding of sterling silver to raise the layer of fine silver so I may enamel the surface.
I used reticulated silver in many of my designs (still do) for
several years. Some variety of silver/gold depletion is usually one
of the steps before the final reticulation heating. Hoover and
Strong has a pretty good encapsulated description on their web site.
Thomas III
Surface Enrichment?
Back in the days when I worked for a major UK silver company we
produced silver coinage in both 62.5% silver-copper and 50%
silver-copper grades. The surfaces of these coin were oxidised and
then acid treated to remove the copper oxide leaving a silver-rich
surface layer which was consolidated by burnishing. We termed this
process surface enrichment and I spent many hours examining sections
of ‘surface-enriched’ coins under the microscope to determine that
they had the correct thickness of silver present on the surface.
So, following Jim’s defense of ‘depletion’ as been gold specific, I
offer this as an alternative description
Charles Allenden
Coper is oxidized by heating in the presence of air, copper oxides are soluble in an acid aka pickle, copper oxides dissolved silver left behind.
James Binnion and all – first I want to thank you for your generous
and knowledgeable contributions to this group. I don’t post often,
but I do read every day and I appreciate learning from what you all
contribute.
I know that when I want to build up the fine silver layer on a sheet
of sterling silver, I heat it in an oxygen atmosphere, pickle the
metal, burnish it with a brass brush and then repeat the process
several times.
I have done this process for years - but have always been curious
about the details of the process and what is really going on – and
if there is an optimal way to do it. If I want to build this layer up
faster / thicker – am I better off heating the piece longer so I
oxidize the copper deeper in the surface of the metal (or does it
only go so far no matter how long I stand there keeping the metal at
temp)? Or am I better off leaving it in the pickle longer to etch the
copper deeper (or does it only etch so far no matter how long I leave
it)?
Is the optimal temperature about the annealing point?
How important is the burnishing part of the procedure? Does it allow
the oxygen atmosphere to get to the copper more easily with repeated
heatings?
Thanks in advance for sharing your knowledge.
Deb
This is wonderful Janet. Just the term we’re perhaps looking for. Do
you all think it’s worth Rio changing the wording on the Aura 22
instructions to reflect that? It seams as though Depletion Gilding
is inaccurate. Or would it only cause more confusion? I would like
us to be accurate.
Mark Nelson
Rio Grande Technical Support
1-800-545-6566
If I want to build this layer up faster / thicker -- am I better off heating the piece longer so I oxidize the copper deeper in the surface of the metal (or does it only go so far no matter how long I stand there keeping the metal at temp)? Or am I better off leaving it in the pickle longer to etch the copper deeper (or does it only etch so far no matter how long I leave it)?
Heating longer is not such a good idea, better to do more cycles of
heat and pickle. Oxygen can easily travel into the silver matrix but
acid can only reach the upper surface so it cannot dissolve the
copper oxide deep into the matrix.
James Binnion
James Binnion Metal Arts
Surface Enrichment?
Surface enrichment, Silvering, depletion silvering, raising the
silver any or all the above. Just not gilding, that refers to gold.
James Binnion
James Binnion Metal Arts
Back in the days when I worked for a major UK silver company we produced silver coinage in both 62.5% silver-copper and 50% silver-copper grades. The surfaces of these coin were oxidised and then acid treated to remove the copper oxide leaving a silver-rich surface layer which was consolidated by burnishing. We termed this process surface enrichment and I spent many hours examining sections of 'surface-enriched' coins under the microscope to determine that they had the correct thickness of silver present on the surface
Surface enrichment sound like you’re adding, not taking away.
Something else to keep in mind regarding this topic and all other metalsmithing nomenclatu
We as metalsmiths not only need to understand each other regarding
any technical term - such as depleting - those same terms must also
be clearly understood by the general public.
Jeff Herman