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Depletion gilding silver. Why?


#1

Can someone explain why this process is called depletion gilding? I
want to know, so that I can explain it when someone else ask me.

Regards,
Andrea Streicher
Streicher Studios


#2

Hi, Andrea- Sterling silver is an alloy of 97.5% silver, 2.5% copper.
When you depletion gild silver, you are first heating the silver until
the copper near the surface oxidizes, and then dissolving out the
copper oxide by pickling. The result is that the surface area of the
silver has a much lesser copper content than the interior. You are
gilding the surface with fine silver simply by depleting the copper
from it, hence the term “depletion gilding.”

Lee Einer


#3

Hi Andrea, A more general term which is sometimes used is depletion
plating. Let’s say you have a piece of sterling silver. Through and
through, the alloy is 92.5% fine silver molecularly interspersed with
(typically) 7.5% copper. When you depletion plate this piece of metal,
you repeatedly heat it, then quench it, and then place it in some sort
of acid. The heating tends to draw the copper molecules to the
surface. The acid dissolves the copper, but not the silver. The
result is that you develop a somewhat porous layer of fine silver on
the surface of an otherwise sterling silver object. The copper on the
surface has been depleted from the alloy leaving the piece in effect
plated with fine silver. The same thing can be done with certain gold
alloys, particularly red golds which have a relatively high
proportion of copper. In this case, the object develops a higher
karat gold content on its surface so we might say it is gilded. HTH,
MP


#4

Andrea, It’called depletion gilding because the copper in the alloy at
the surface is depleted through going into solution with the acid
leaving a high karat gold film. Gilding of course is a process of
leaving a thin coating of gold on a surface by any means. Jerry in
Kodiak


#5

Hi Andrea,

Depletion gilding is named that way because the alloying metal
(copper in the case of sterling) is ‘depleted’ from the sterling when
the metal is pickled.

The idea is to have a top layer of mostly fine silver (or at least
greatly reduced copper content).

Typically, to depletion guild a sterling item, it’s heated & pickled
several times. It’s usually hand brushed with a soft brass brush &
lubricant (soapy water) between picklings & the next heating.

The higher concentration of fine silver on the surface has a little
different color & the piece doesn’t tarnish quite as easily.

Dave


#6
Hi, Andrea- Sterling silver is an alloy of 97.5% silver, 2.5% copper.

Lee, You’ve got it slightly wrong. Sterling silver is 92.5% silver,
7.5% copper. Thus the international designation “925”.

Joel Schwalb
@schwalbstudio
http://www.schwalbstudio.com


#7

Hi Andrea

The short answer (in my case) is to avoid firescale when i enamel.

The long answer is below.

To bad we don’t have some scanning electron micrographs (electron
back scatter mode, or better yet a photo of energy dispersed x-rays -
jargon but the pictures are fabulous) of sterling silver around. What
would we see is small lighter areas surrounded by darker ones, in the
ratio of 7.5 to 92.5, the same as the ratio of copper to silver. We
would be looking at a surface and consequently in our mind’s we need
to imagine that light areas are the surfaces of small units of copper
in a matrix of silver.

Metals have differing solubility coefficients in various acids and
bases. For example section B of the CRC Handbook of Chemistry and
Physics lists copper as being very slight soluble in hydrochloric
acid (HCl) and does not list the solubility of silver in HCl, implying
that it is insoluble in this acid. So, if we put a piece of sterling
in HCl and waited an awfully long time the acid would dissolve the
copper on its surface layer and leave the silver (in theory).

To speed things up we can heat the metal to form metal oxides which
are more soluble than are the metals. Common practice has revealed to
us that the oxides of copper are more soluble in acid, specifically
sulphuric acid (guess where i live? ) than are the oxides of
silver. Again common practice has revealed to us that if we heat
sterling lightly (I go to just black to form CUO2), cool, dip in acid
for some time, lightly scrub, rinse and dry, and repeat the preceding
about six to eight times (dare i say seven?) we will end up with a
very thin layer of pure silver on top of our sterling. We can put this
in our kiln and it will not have very much fire scale, if any, at all.

I was taught this method as part of the process for champlev�
enamelling for which one creates pits in the silver with gravers. We
used sterling rather than fine silver because it is easier to engrave.

Similarly one can also deplete gold alloys for the same reason.

I have used depletion with jeweller’s bronze (Cu:Zn, 80:20) to remove
some of the zinc from the surface because of its great propensity to
form scale. Enamelling on this metal is hit or miss but can produce
some interesting effects.

Finally, does any one know of a table listing the solubility
coefficients of metals and oxides in the mineral acids, and where it
can be found?

Hope this helps.
David


#8

Not to be too picky but… the process is not called depletion
gilding. if you are working on a silver copper alloy like sterling.
It could be called surface enrichment If however you were doing a
similar type of process (heating , pickling, brushing ) on a gold
copper alloy it would be depletion gilding. Websters defines it as
follows

Main Entry:	1gild
Pronunciation:	'gild
=46unction:	transitive verb
Inflected Form(s):	gild=B7ed /'gil-d&d/; or gilt /'gilt/; gild=B7ing
Etymology:	Middle English, from Old English gyldan; akin to Old 
English gold gold
1 : to overlay with or as if with a thin covering of gold
2 a : to give money to b : to give an attractive but often deceptive 
appearance to c archaic : to make bloody
- gild=B7er noun
- gild the lily : to add unnecessary ornamentation to something 
beautiful in its own right


@jbin
James Binnion Metal Arts
4701 San Leandro St #18
Oakland, CA 94601
510-533-5108


#9

Hi Andrea,

You can’t enamel sterling silver but you can enamel fine silver. But
sterling silver has advantages of rigidity so if you want to put
enamels over sterling silver, just depleat the surface changing it
into essentially fine silver.

hale


#10

I have done ‘depletion gilding’ of gold with a boiling mixture of
potassium nitrate, salt and sulphuric acid. We call it ‘colouring’.
But I think silver would just be dissolved in this evil mixture. I
don’t see the sense of calling anything ‘gilding’ when applied to
enriching the surface of silver by dissolving out any copper content

  • but perhaps I should get out more.
    David Kelsall UK

#11

I have done ‘depletion gilding’ of low carat gold with a boiling
mixture of potassium nitrate, salt and sulphuric acid. We call it
’colouring’ here. But I feel sure that silver would just be dissolved
in this evil mixture. I don’t see the sense of calling anything
’gilding’ when applied to enriching the surface of silver by
dissolving out any copper content - but perhaps I should get out more.
David Kelsall UK


#12

Hi Gang,

   I don't see the sense of calling anything 'gilding' when applied
to enriching the surface of silver by dissolving out any copper
content - but perhaps I should get out more. 

Here’s a ‘possible’ reason why the repeated heating & pickling of
sterling to raise a fine silver layer is called ‘depletion gilding’.

Suppose some observant craftsperson/marketeer long ago noticed during
their bench work that a sterling piece that had been heated & pickled
several times tended to resist tarnishing better than unheated/pickled
sterling. Realizing that this could provide an advantage when selling
his products he creates a name for the process.

Since many consumers are familiar with the term & process of gilding
a light goes on. “Ah ha he thinks, I’ll call the item ‘depletion
gilded’”. The word ‘gilded’ is already understood by many & the word
’depletion’ adds an air of mystery, thus, possibly increasing the
value in the eyes of the consumer.

Understand the terminology may be completely incorrect from a
technical point of view, but the term came into popular use & now
we’re stuck with it.

Now, this may all be conjecture, but it might have happened.

Dave


#13
Understand the terminology may be completely incorrect from a
technical point of view, but the term came into popular use & now
we're stuck with it.

No, that is one of the reasons for forums like this it to help to
correct terminology and technique Calling a Cubic
Zirconium a Diamond does not make it so and calling raising the
silver content on the surface of a piece silver alloy by depletion
is not gilding . The only people who are even remotely aware of these
terms are metalsmiths so it is not a public education problem it is
one of just learning to call something by its proper name.

Jim


@jbin
James Binnion Metal Arts
4701 San Leandro St #18
Oakland, CA 94601
510-533-5108


#14

Enamelists use a “flux”, and the only resemblance between it and a
jeweler’s is that they both might contain boron.

So given the above we can see that the craft is replete with
inconsistencies. So what.

Regardless of what we speak, the language is a convention with the
rules made up after the convention is reasonably well established. The
only problem is that the bloody convention keeps changing and the
rules just lag behind. It’s the concept of “normative” versus
"prescriptive", and I would rather go with normative any day. Our
language is alive and evolves.

For example, it is now OK to certainly split the infinitive in
English . We who speak the language make its rules, and
regardless of what an authoritarian rule setter says about words, my
metalsmithing and enamelist friends know exactly what I mean when I
say I hard-soldered a backing to a piece of sterling which was
depletion gilded prior to using a silver flux. Grammarians follow
behind the pack, they do not lead it. We may use jargon but it is
useful jargon. Those outside the craft might not even care. What they
do care about is a good product at the end of journey.


#15

Rather than calling it “depletion gilding”, (which I agree seems
confusing when one is referring to silver), my former teacher always
called it “bringing up the fine silver”. I have used this term for a
long time, and it seemed (or so I thought) that it was in general
use. We (those whom I have heard using this term) all knew we were
really leaching copper from the surface, and that that was how it
worked. I suppose if you wanted to be really picky, “bringing up the
fine silver” could connote that you were somehow transporting the
silver molecules from the inner structure to the outer surface, and
that too could be misleading. How about depletion silvering, then?
Copper molecule dissolution? Preferred molecule selection? ( The last
one makes me feel as if I am discriminating against copper molecules.
What a shame…there they are, working their atoms off when we need
them, only to be ditched at the final moment of glory, when we decide
that their task is complete, and they’re not quite presentable enough
to make it into the spotlight.) Seriously, is there a consensus on
the most prevalent term for this process? Lin


#16
    ...  my metalsmithing and enamelist friends know exactly what I
mean when I say I hard-soldered a backing to a piece of sterling
which was depletion gilded 

David, why not say depletion silvered?

Bri
B r i a n � A d a m
http://www.adam.co.nz/workshops/usa2000/


#17

the term for gold is depletion gilding, for silver is sepletion
silvering…

Charles

Charles Lewton-Brain
Box 1624, Ste M, Calgary, Alberta, T2P 2L7, Canada


#18

Hello folks. Your is 100 % wright,Joel.Sterling silver is
925,but you could have other alloy’s, but they are not mentioned as
sterling silver.By the way Andrea,the name silver may be used up or
down to an alloy consisting of 800 parts of silver and 200 parts of
othre material.Lower silver alloys may not use the name silver and as
far as I know about the trade tradition,the stamp of silver in lower
then 800 may not be used,so no stamp of a moon and a crown.

Regards Pedro
Palonso@t-online.de