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Dr. Harris: We're going to talk about bronze casting
and maybe begin a little bit with the history
of the medium and what we're looking at is a recovered
ancient Greek bronze sculpture that looks like it's been
through some hard times, but it's important to remember
that that's how ancient Greek sculpture looked.
It was cast in bronze and when we're in the museums,
what we're looking at mostly are Roman copies
in marble of what were bronze sculptures
made by the Greeks.
Dr. Drogin: That's right.
A lot of the classical figures that were created
by the ancient Greeks, like this one
from around the 3rd century BCE,
were made out of bronze.
Then, when Roman culture developed, they were very,
very good at making copies of the Greek bronzes.
Most of the Greek bronzes have been lost,
they've been melted down.
Very few survived, this is one of them.
Oftentimes the ones that survived were lost at sea
and so were well-preserved underwater, like this one,
which is why it has that mottled finish.
That wasn't originally how it looked,
but you're absolutely right.
A lot of the things that we think of
as typical Greek sculpture in marble are actually
Roman copies in marble of the Greek bronze.
Dr. Harris: Also, the bronze was often melted down
during the middle ages, because first of all,
these are just pagan sculptures
that Christians didn't care about in the middle ages,
but also bronze was and still is a valuable metal.
Dr. Drogin: It's very, very valuable metal.
Mostly made out of copper and tin and it's expensive,
just in terms of a raw material, that's right.
So if you don't like the sculpture that's made
out of bronze, you would rather melt it down
and make it into something that you do like.
For instance, a church bell or a cannon.
Those are the kinds of things that, oftentimes,
when marble sculpture -
Excuse me, when bronze sculpture was destroyed
that was often why it was.
Dr. Harris: Let's look at another example
of a bronze sculpture from the Renaissance.
Dr. Drogin: Okay, here is a Renaissance example.
This is a small bronze copy of the Apollo Belvedere,
dating from the early 1500s.
The sculptors name is Antico, which of course,
is not the name that he was born with.
He got that name because he made small bronze copies
of things from (crosstalk)
He worked mostly for the Gonzaga family in Mantua
in the early 16th century.
What we can see here is an incredibly highly finished,
very smooth, and even gilded small bronze sculpture.
Dr. Harris: How small is this?
Dr. Drogin: This is approximately, I would say
about six inches tall.
Dr. Harris: Oh, it is small.
Dr. Drogin: It's pretty small.
What's really exceptional about his work,
and this is a good example to talk about bronze with,
is that it does have this very, very smooth finish
and a lot of detail and then, of course,
some very nice gilding, as well.
Dr. Harris: The ability to cast bronze, and we'll talk
about that in a second, had been lost
during the middle ages and it's rediscovered
in the Renaissance.
Dr. Drogin: That's right.
Bronze, aside from things like church bells and,
later on, artillery, is not something that people
in the middle ages were very interested in.
So the process of casting bronze for art, for sculpture
wasn't something that was done very much,
especially in a large scale.
It is something that, in the Renaissance,
they start making foundries again to create
this kind of work.
Let's talk about process a little bit,
because when we're looking at the finished product,
it might be very spectacular to the eye, but in fact,
it doesn't reveal very much of how it was made
and in fact, the making of the object
is purposefully hidden behind the pristine finish
that we see a lot, especially in Renaissance sculpture.
Let's look at a diagram that explains the process
that was current.
Dr. Harris: This process is called?
Dr. Drogin: This is the lost wax process,
which is a process that the ancients used
and then is used again in the Renaissance.
Dr. Harris: And still used today.
Dr. Drogin: Oftentimes used today, that's right.
The first step is that you want to create a core.
You want to create not what your finished sculpture
is going to look like, but just the general shape of it
out of clay.
That is what you're looking at in the very center
of this diagram.
The next step, then, is that you want to cover that core
with wax and it's just a skin, just a couple
of centimeters thick.
That wax that you're molding and adding on,
you want to give that the appearance that you want
your final sculpture to have.
Dr. Harris: Really you're kind of carving first out of wax.
That's right, but technically speaking,
you're not even carving.
This is technically an additive process,
because you're adding wax on.
So if you make a mistake, it's okay, it's just wax.
You can take it off, you can add it on again,
but you basically want to think of it as the skin
on top of that clay core that's going to give you
all the details that you actually want.
The next step is you're going to stick some pins,
as you can see here, through the wax
that's in the middle layer, into your clay core
and then put more clay around the outside.
You've basically created a sandwich with a clay core,
your wax skin, and then more clay
that is around the outside with pins holding
everything in place and we'll see why that is
in a second.
Dr. Harris: The clay would have to harden.
Dr. Drogin: That's right, you do want the clay to harden.
The next step is you're actually going to heat up
the whole thing.
You're going to stick it in a furnace
and that is when all of your wax is going to melt,
which is why this is called a lost wax process.
Dr. Harris: So we're losing the wax.
Dr. Drogin: The wax is gone and now you can see
why we have those pins there,
because when the wax disappears,
if there weren't these pins holding everything in place,
the clay core in the middle would drop down
and it wouldn't give you the space where your bronze
is going to go.
Dr. Harris: So you're kind of creating a mold.
Dr. Drogin: That's exactly what you're doing.
The next step is, as you can see in this side
of the diagram in B, you want to pour
your molten bronze into the mold
and the bronze is going to go everywhere
that the wax was.
That's why you wanted your wax to basically look
exactly like what your finished product is going to be,
because that bronze is going to take all of that up.
Dr. Harris: So you're pouring really hot bronze.
Dr. Drogin: Hundreds and hundreds of degrees fahrenheit
and it's molten.
Dr. Harris: Dangerous.
Dr. Drogin: Very dangerous.
It's very hot and you pour it in and then,
once you filled it up and you think
that the bronze has gone everywhere you need it to go,
you let it cool off.
You let it cool and you let it cool and then finally,
you break the outer mold and that will reveal
your bronze sculpture that's essentially going
to look like the was that you had put on it before.
The clay core is oftentimes just trapped inside.
In a lot of bronze sculpture it's still in there.
You don't want to necessarily get it out.
It doesn't matter.
If you want, you could leave an area of bronze open
and reach in with a stick and poke it around
and shake it out.
Oftentimes the clay core is still inside.
The thing is, when you've removed your outer layer
of clay and it finally reveals the bronze,
the bronze is very, very rough.
Your sculpture is not finished by any means.
It has a lot of bubbles.
It's very -
Dr. Harris: Imperfections.
Dr. Drogin: A lot of imperfections, plus you also have
all of these pins that are still sticking out of it.
So the next process, which is incredibly time consuming
and oftentimes the most time consuming part
of making a bronze sculpture, is finishing or chasing
the bronze.
You want to polish down the areas you want
to have smooth, get rid of any imperfections,
cut off the pins and other things
that might be sticking out.
This is a very, very labor intensive process.
At this point, if you want to think of it in this way,
you're actually working reductively now,
because you're removing anything, taking away things
that you don't want there to be anymore.
It's at this stage that you can create details
that might have been too fine to achieve
with the wax that would've been lost in the process.
Dr. Harris: So would you reheat the bronze
to make these?
Dr. Drogin: You can do that.
Dr. Harris: Like the ones we see on the helmet here
of Goliath from Donatello's David and Goliath?
Dr. Drogin: This is the head of Goliath
from Donatello's sculpture of the mid-15th century
and you can see things like the texture in here
and between these vegetal designs or the texture here,
this kind of hammering that give you
these circular texture marks even here,
like on the sandals.
This is all created afterwards, the fine details,
even like eyelashes or other kinds of things
on other sculptures.
Dr. Harris: Just by hammering.
Dr. Drogin: Just by hammering.
Then -
Dr. Harris: Maybe using a stencil and hammering.
Dr. Drogin: You could do that sometimes, as well.
There are whole different tools that different artists
in their workshops would use and of course,
those change slightly over time and in different regions,
but generally remain the same.
Here we're looking at a sculpture by Giambologna
from the late 16th century and this is a good artist
to talk about when we talk about the fine finish
that can be achieved in the end,
much like the first example that we looked at.
It's polished down, sometimes with oils
and even some pigments sometimes.
Depending on the materials that are in your bronze,
of course it can have different kinds of tones and colors,
but the idea is then to give it
this incredibly lustrous finish.
You have, really, no sense of the casting process,
of the wax, of how rough and unfinished it looked
when it was first made.
This is the reason.
All of these levels of technique and procedures
that went into making the bronze, this is the reason why
it's so expensive.
We've mentioned elsewhere that marble sculpture costs
ten times more than wood sculpture.
Well, bronze sculpture costs even ten times more
than marble.
If you're going to make something out of wood,
it might have a certain cost, but if you're going to make
it out of bronze, that same sculpture would cost,
literally, 100 times more.
Dr. Harris: But of course it's much more durable medium
(crosstalk) and even more durable than stone.
Dr. Drogin: It's more durable than wood, of course,
and it is more durable than marble.
Marble, although it's a rock is very brittle.
You can think of it almost like chalk.
So marble can't really stand on its own two feet,
if you want to think of a large sculpture.
(crosstalk)
Bronze, instead has incredibly good tensile strength
and so you can achieve things in bronze
that you would never be able to achieve in marble.
Dr. Harris: Mmhmm (affirmative).
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