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Shibuichi depletion guilding


#1

Greetings Metalmasters: How do you do depletion gilding on
shibuichi? If you heat it one temperature, you get a heat patina. If
you heat it another temperature, you get depletion gilding. How do
you know the difference. Does the shibuichi conveniently glow some
color or blink on and off some message in Morse code?

Sally Parker


#2
Greetings Metalmasters: How do you do depletion gilding on
shibuichi? If you heat it one temperature, you get a heat patina.
If you heat it another temperature, you get depletion gilding. How
do you know the difference. Does the shibuichi conveniently glow
some color or blink on and off some message in Morse code? 

There is not really a difference. If you heat it up it oxidizes, if
you pickle it removes surface oxide if you repeat the process you
begin to enrich the silver content of the surface. If you leave it
alone you have a heat patina.

James Binnion
James Binnion Metal Arts


#3
Metalmasters: How do you do depletion gilding on shibuichi? If you
heat it one temperature, you get a heat patina. If you heat it
another temperature, you get depletion gilding. How do you know the
difference. 

Sally, your problem is in your description of the resulting look.
With depletion gilding, you’re heating it to whatever temperature is
needed to oxidize the surface. That, initially, is a heat patina.
Then you pickle it. That removes your “patina”, along with the
oxides. The trick is that not everything in the Shibuichi (or
whatever you’re treating) oxidizes. In this case, it’s the copper
content, oxidizing to copper oxides. The other componant of the
alloy, silver, does not significantly oxidize. Pickling removes
copper oxides, but leaves the unoxidized silver. You repeat this
several times. Eventually, you’ve removed enough copper from the
surface, in the form of the oxides that develop, that subsequent
heating is no longer able to bring copper up to the surface to be
oxidized, as the silver layer has become too thick. So now, you’ve
got Shibuichi with a silver rich layer on the surface. That surface
now looks like silver, no longer the color of Shibuichi. That is
what’s called depletion gilding. The effect is somewhat similar to
electroplating (which is the modern method of “gilding”), but you do
it by removing the portions that are not silver from the surface,
rather than covering the surface galvanically with an additional
layer of silver. Like an electroplated surface layer, the surface is
silver, and a silver color, and unless you then go an put a patina on
the silver surface (such as liver of sulphur treatment), this
depletion gilded surface does not have a patina. It looks like clean
pickled metal, or the same that’s been scratch brushed, if you do
that step (recomended, as it burnishes and compacts the surface
layer. Use a soft brass or nickle silver “platers brush”. These are
gentle enough to burnish the surface, but not to scratch off or
remove any of it. Note that repeated heatings and picklings serve to
make the depletion gilded layer thicker. You don’t have to do this if
you don’t want. The silver color may develop with the very first
heating and pickling cycle in some cases, and if you like the look,
feel free to stop there. But thicker depletion gilded surface layers
will be more durable, and less likely to change color over time.

Peter


#4

hello sally

because shibuichi is an alloy (it’s name means “one fourth” in
japanese) you are starting with 3 parts copper to one part silver…
I guess my question is what are you trying to do…get a more
silvery-pink colour out of your metal or… depletion guilding is a
standard process using acidic baths ( pickling) to raise a layer of
precious metal to thje surface if you keep pickling shibuichi you
will be- really just making a very saturated ( deep blue from cupric
oxides) pickle solution- great for granulation, a glaze for raku,
etc… why not make a sheet of alloy containing higher silver
content… I suppose I’m unclear on what you’re after…as you seem
to know what/how depletion gilding is…rer