JOHN DELANEY: We want to thank
you very much for coming
to the lecture today, in which
we're going to talk about
beyond what the eye can see
using technology of NASA's
rovers to explore paintings.
The lecture will be given
by myself, John Delaney and Kate
Dooley.
We're both in the research--
scientific research department
at the National Gallery here.
So what I'm showing you
on this slide here
is sort of the typical images
collected and all the sort
of major museums
around the world when you look
and study paintings.
Of course, you get a very
nice, high resolution color
image.
You get an x-ray, which we're
all familiar with.
This is related
to optical density
of the materials, usually things
like led white shows up.
And then you get something
called an infrared reflectogram,
an image taken in the infrared.
And then the infrared
is the portion of light that
is beyond the visible.
So the range just beyond, not
the range
where you start to really feel
heat, but in the range
that you can see by eye.
And essentially, in this range,
you're
able to get below the paint
layer and see original sketch
marks or drawings
or other compositions.
You can see there is a woman
beneath this painting
here by Pablo Picasso that has
sort of been covered over
by the painting of the boy
here, Le Gourmet who is eating
out of this bowl.
So as I said,
these are currently the images
taken today.
And what we're going to talk
to you today about is new images
that are being taken to answer
fundamental questions related
to, is the painting
by the particular artist
of interest
and how has it changed
and what materials were used.
Now, how do we actually look
through a painting to see
the under layer
of preparatory sketch?
Well, the trick is we have
to find a way to get
through the upper layers
of paint.
This is a cross-section here
taken from a painting showing
paint layers, a ground layer,
and then some black lines here,
black material here, which
is the under drawing line
or the preparatory sketches.
So to see
through the upper paint layers,
we have to take advantage of two
effects.
One is to minimize
the absorbance.
This equation here describes
the transmission of the paint
layer, which is basically
proportional to scattering
by the particles, pigment
particles, and absorbance
by the pigment particles.
Two things happen when you go
in the infrared
outside the visible.
You get less absorbance.
You also get less scattering.
And scattering
is an important component.
Snow, for example, is white.
It doesn't absorb any light.
It only appears white to us
simply by the scattering effect
by itself.
So it's a combination
of scattering and absorbency
it provides for the color.
And so when you have light
coming into this notional paint
layer, you have light laterally
around and the visible picking
up being selectively absorbed
and emerging out with a color
change to it.
But if you go into the infrared,
we have light passing through,
not being absorbed minimizing
the scattering,
reflecting off the preparatory
ground layer
and up to the camera.
Light which
red light or infrared light
that strikes an under drawing
line, which is preferentially
absorbed more by, compared
to the white ground layer,
it's absorbed and less light
goes back into the camera.
So we get a contrast difference.
Well, it was a kind
of a nice dramatic example you
can show of why you can minimize
lights scattering by going
to the infrared.
And anybody who's gone to Los
Angeles
is very familiar with the fog.
I'm sorry and especially
the haze in the sky.
This is a picture,
a black and white picture, taken
from the painting conservation
studio at The Getty.
And you can see it's very hard
to see the mountains
in the distance
in the visible due
to the aerosol and smog
in the air.
But if we go
to the near infrared,
the same region we look
through the paint layers
in the paintings,
you can see we can penetrate
that atmosphere.
And we can see the mountains
quite clearly as well as a lot
of the objects in the distance.
So you can sort of think
about the atmosphere in between
as essentially being
analogous to those paint layer
particles.
So by going into the infrared,
we minimize absorbance of light
by the pigments and minimize
the scattering.
Well, when you do that
and you use that technology
to look at paintings,
you go from the color image
to this infrared image.
And the infrared image can give
you a lot of information
about changes in composition
that the painter may have
actually decided to make.
In this case, he's essentially
changed what would be
a Romanesque church
into a more contemporary
to that time period.
You can see a lot of drawing
here, these arches and the like,
that didn't make it
into the final composition.
These can be revealed.
You can also see that Christ,
this is a painting by van Orley
of Christ among the doctors.
You can see that he's
on a pedestal in the drawing.
But that was not carried
through the final painting.
Now when you look very closely,
and when you bring
these pictures in register,
you can see we can understand
how all these little changes
were made by the artist
and then how it was finally
executed in paint.
And one of the things that shows
up kind of nice
is if you look at this edge
of the final painting
of this arm,
when he initially drew them,
this arm was up much higher.
And he decided to make
this foreshortening
with his correction to,
for the final composition.
And you can also see this fellow
here has several noses trying
to get the right orientation
right.
OK, so that's
sort of a classical example
of drawing, under drawing.
This is a painting I'm sure most
of you are familiar with,
painting by Leonardo da Vinci
in the collection here ,
Ginevra.
There is a tremendous amount
of lead white, which is used
to make this incredibly lovely
luminescent face.
And underneath here, there'll
be some sort of drawing
or preparatory sketch.
And when we go to the infrared
to make it rendered visible,
we see--
we don't see drawings right?
We see actually individual dots.
So this has essentially been
transferred in a stenciling
process, a pouncing process.
Apparently he had made a sketch
of the young woman
and then pricked holes in it
and then transferred it
onto white board that was
probably still tacky with led
white.
And you're seeing essentially
the carbon dots left over.
So this tells us quite a bit
about that he didn't start
drawing with a board.
And for a curator
and conservator, these types
of images have a lot of meaning
about how these paintings were
prepared, when they were
prepared,
and some of the details
in the painting process.
Now, besides looking
for drawings and preparatory
sketches, we can also visualize
some of these what we're going
to call painted
compositional changes
that a painter decides to make
changes to the composition.
In this case,
for Feast of the Gods,
a painting that's been worked on
by at least three painters
but certainly started by Bellini
and finished by Titian,
and maybe Dosso Dossi
in the middle.
And so there are a lot
of compositional changes
in these paintings,
this painting that has occurred
over time.
By taking an image
in the infrared,
you can see quite clearly
this hillside was originally
a stand of trees.
So the original composition
consisted of a stand of trees
with the gods in the foreground.
At some point this change
was made.
And my colleague, Kate Dooley,
will talk more about what we can
learn beyond just simply there
was a stand of trees
in the background.
Now, what I've shown you so far
is just taking pictures
in the infrared broad banded
without actually worrying too
much where we look.
Well, what I want to try to show
you in the slide
is that by leveraging techniques
that NASA has used for years,
by taking different pictures
and different spectral bands,
we can see small differences
that relate to materials.
And that can give us more clues
as to how the compositions were
put together.
So what we're going to do
is look at three images taken
where we swap out
different filters in front
of our camera.
The painting here is Little Girl
in a Blue Armchair by Mary
Cassatt in the collection,
a very lovely painting.
And I'm essentially going
to show you these stacked up
like cards in a playing deck
where we're going to go
to longer wavelengths
in the infrared.
So there's our visible image.
That's the first infrared image.
Going a little further out,
you can start to see
little differences.
But they do look very, very
similar in many ways and then
the third one.
Well, if we put them
all together in a stack,
and you start to look
and compare, you can start
to see there's a little bit
of an edge difference here going
on.
Well, looking at a lot of images
side by side
to look for subtle changes
takes a lot of time.
It's not very efficient,
and you can miss things.
So a technique that has been
used for a long time
is essentially called, to make
a false color image.
So we're going take those three
images in the infrared
and pretend we're going to make
a color image out of them.
We'll take one closest
to the visible part
of the visible range
in the infrared.
Put in the blue gun.
Put the next one
in the green gun in the red
and make this false or, what
some people like to call,
artificial color image.
And a couple of things
jump out at you now that were
hard to see before.
Everybody see where the dog was
originally?
Yeah, the dog was on the floor.
Now, this was a painting
that Mary Cassatt got advice
from Degas on.
So we know there are
some changes that were made
in this composition.
What we know as scientists is
there are compositional changes
in the material.
We know these blue chairs
in the background
have something odd about them.
There is this reddish color
and then there is the loss of it
in this armchair here
in the high part.
So we know that this was
extended upwards.
This was painted in using
a different set of materials
than these guys.
Maybe it's hard to see,
but this gaze of the girl
has changed.
And we know that the dog was not
originally in this chair.
So they're all pieces
of information that come out
by constructing this false color
image that give more information
to the curator
as to possible ways
that Degas may have influenced
the changing of this painting.
So essentially our goals are
beginning to shift,
I think you can see.
We want to determine
if the changes we're seeing
in the infrared
are just initial drawings or are
they partially completed
paintings?
Or are they finished paintings,
which were basically been
covered over
abandoned by the artist?
And essentially this means
we need to go beyond just taking
good pictures to actually having
some ability to map
and to identify the pigments
that are being used
in the composition.
And now I'm going to switch
the talk over to my colleague,
Kate Dooley.
KATE DOOLEY: Artists use
many pigments.
And a lot of them are minerals.
And so in this example here,
this
is an illuminated manuscript,
Christ in Majesty With Twelve
Apostles.
And there's
many different pigments used
in this composition.
M this yellow robe
of this gentleman
here is a yellow ochre, gothite,
which is an iron oxide
hydroxide.
There's ultramarine used in some
of the blue shadows of Christ's
robe.
And ultramarine is a sodium
aluminum silicate that contains
sulfur.
Red lead, a lead oxide,
is used for some
of the red robes
of the apostles.
There's also red ochre present,
which is hematite which
is an iron oxide.
So that's used for some
of the hair.
And then azurite is used
for the floor.
And azurite
is this blue mineral.
It's a copper carbonate
hydroxide.
So NASA is also
interested in identifying
minerals, particularly
on the surface of Mars.
So they have tools to do that
with their Mars rovers.
They have different technology.
So one thing they have is
multi-spectral imaging
with their pancam system.
So they have a detector
that they use
with different filters,
which I'll talk about.
And then they have
an x-ray spectrometer.
And then they also use a Mars
reconnaissance orbiter where
they can do
hyperspectral imaging, which
I'll explain here in a minute.
But they're also
interested in identifying
minerals on the surface of Mars.
So we use--
So here's an example
of their spectral imaging
they can do with their pancam.
So this is a false color image
here.
And you can see
the spherical particles here
that appear blue,
these blueberries.
And these are
spherical accretions they know
are minerals that formed
in a wet environment.
So particularly hematite,
they know formed
in a wet environment.
And they can identify hematite
by looking at how
the reflected light intensity
varies with wavelength.
So they use a detector
with different filters.
And then they can--
these large black circles
you see here are how the-- are
their data points
from their pancam.
So this is a plot
of the reflected light intensity
versus wavelength.
And just to orient yourself
to these plots, wherever you see
a dip in this curve
is where you have a lower amount
of reflected light intensity.
And alternatively, you can think
of that, that there's absorption
of the light there.
And these absorption features
you can use to actually do
identification of the materials
that are present.
So we use very similar
spectral imaging techniques
at the gallery as the pancam.
So, for example, this
is a cutting
from an illuminated manuscript.
This is the Praying Prophet
by Lorenzo Monaco.
And this is an example
of our multi-spectral imaging
system at the gallery.
So we have a detector.
It's a silicon CCD.
And then we have an imaging
lens.
And then we have a filter wheel
on the front of this that we can
rotate and put different filters
in front of our camera
that pass different wavelengths
of light.
So here, for example, this
is an image of the painting
where we used a 400 nanometer
bandpass filter.
And this is what you see.
And so this
is a monochrome image.
And you're seeing contrast based
on differences
in the reflected light
intensity.
So your darker areas like this
reflect less light then
your brighter areas.
So you can rotate and use
different filters in front
of that camera.
And you can see how
the reflected light intensity is
changing with wavelength.
And so what you end up with
is you end up with this stack
of images.
And so you have the stack
of images, and they correspond
with different spectral bands.
Because we've used different
filters to pass
different wavelengths of light.
So one thing that you can do--
oh, the other important thing
when you're taking
these spectral images like this,
we include
these black and white standards
you see here.
They're reflectance standards
so they have known reflected--
they reflect light in a known
way.
And so it's important that you
calibrate all your images
to these same standards.
Because the filters that you
use, they can have
different transmission
properties of light.
But if they're all calibrated
to these same reflectance
standards, then you can actually
really start comparing how
the reflected light intensity
varies
in these different images.
So that is what that is
depicting calibrating our images
to reflectance.
So then what you can do, say you
can look at, there's a pixel
here in this blue leaf.
So now what I can do
is see how the reflected light
intensity varies in each
of my spectral bands.
So the yellow rectangle
you see here, it's 40 nanometers
in width.
Because that's the width
of my bandpass of my filter.
It's passing light.
It's centered at 400 nanometers.
So it's passing light
from around 380 nanometers
to 420 nanometers.
So then you can look
at this pixel.
You can see the average
reflected light intensity
in this spectral band.
And then you can plot it here.
So you can do the same thing.
You can look at the same pixel
in all of these images.
And now you can plot how
the reflected light intensity
varies with wavelength.
So then you can-- it kind
of looks like connect the dots.
But now you start seeing
a reflectance spectrum.
So that's just a plot
of the reflected light intensity
versus wavelength.
And you can certainly, when you
have data like this,
you can certainly start
separating materials.
And for some materials that have
simple reflectance spectra
like this, you can start to do
identification.
So this blue pigment here,
there's a low amount
of reflected light intensity
centered at 600 nanometers.
So there's absorption
of the light here.
And this is actually
indicative of ultramarine.
It has a very intense absorption
at 600 nanometers.
So from this, we can actually
start to identify the materials.
So with a data set like this,
we have a stack of images.
So we can look at the data
as images.
But you can also drill
through your stack of images
and look at reflectance spectra.
So you can look at images
or spectra.
And then once you have
the spectra, you can actually
start doing material
identification.
So NASA does this
with their pancam system.
So they've identified gothite,
which is this iron oxide
hydroxide right here.
And that's this spectrum here.
So the data from their pancam
images are represented
by these large, black circles
here.
And based on where the light is
reflected or absorbed,
they can actually identify
gothite.
So we've done the same thing
with our imaging system
at the gallery with our detector
and then our filter wheel.
And this spectrum you see here
is gothite.
And so it was actually used
for these yellow or brown robes
of some of the apostles.
So hopefully it's a little
clearer now how the pancam works
and how multi-spectral imaging
works.
But with paintings we expect
to see a wider variety
of minerals
and different pigments
within paintings than you'd
expect to find on the surface
of Mars.
So we expect to have more
spectral diversity that we're
going to want to identify
in a work of art.
So having-- doing
multi-spectral imaging where you
just sample every 50 nanometers
or so might not cut it
to identify all
of these pigments.
So one thing you might want
to do is actually start doing--
This is an imaging spectrometer
that NASA uses.
And you might want to start
doing spectroscopy where you can
have,
instead of sampling every 50
nanometers, you sample every 3
nanometers or so.
And you can reproduce curves
that look like this
and look more continuous
and less like connect the dots.
And that's important,
because some minerals have very
sharp absorption features.
So jarosite here
in the near infrared,
this dip in reflectance
is where there's an absorption
feature.
And some of these
are very narrow.
And if you were only doing
multi-spectral imaging and only
collecting data every 50
nanometers, you wouldn't be
able to resolve features
like this.
So that's why we want to start
doing spectroscopy.
So spectroscopy in general
is just the study of light
as a function of wavelength.
So we're looking
at diffuse reflectance
spectroscopy.
So we're looking at light that
is reflected from a work of art
as a function of wavelength.
So John went
through this example of how
the absorption and scattering
processes happen within a paint
layer.
And here I'm showing
some reflectance spectra
for four different blue pigments
in an oil binder.
So this was the plot
of the reflected light intensity
on your Y-axis
versus wavelength.
And right here I'm only plotting
light from 400 to 700
nanometers, which
is in the visible spectral range
that your own eyes are
sensitive to.
So all four of these pigments
are blue.
And you can see that they look
relatively similar.
Because they're blue if you just
look in the visible spectral
range.
However, if you extend out
into the near infrared,
so beyond the visible,
you can start seeing that you
see differences here.
And so these differences
and these absorption
features you can use to do
material identification.
So this is a plot of two
different pigments.
And in the visible spectral
region, which is shaded
this kind of blue color, what
you see, the absorption features
are
due to electronic transitions.
So within a molecule,
if you absorb visible light,
it's energetic enough
to actually promote an electron
to an excited state.
And so that gives rise
to these electronic transitions.
And electronic transitions you
usually see in the ultraviolet
or the visible spectral region.
And in minerals,
electronic transitions are what
give rise to the color
of materials.
So for example,
like this dashed spectrum you
see here, it absorbs light
at the blue wavelengths,
the orange,
the green wavelengths.
And then there's
a sharp increase in reflectance
around 600 nanometers.
So this material is actually
vermilion.
It's reflecting light
at a red wavelength.
So this appears red.
This pigment is red.
So and then
in the near infrared, what
you're seeing
are vibrational transitions.
So this has to do
with the motions
of the molecules that are
present.
So you can get absorption
of the light
where there's a dip
in this curve that are
due to vibrational transitions.
So again, we're working
in the part
of the electromagnetic spectrum
where it's visible light where
your eyes are sensitive to,
and then just beyond,
into the near infrared.
So as an example, this is a unit
cell of azurite, which
is a copper carbonate hydroxide.
And so this here
is a reflectance spectrum
of azurite paint.
So in the visible,
there is a strong absorption you
see here.
So this
is
due to an electronic transition
that's causing this absorption
of the light.
But the blue wavelengths right
here are reflected.
So azurite is a blue pigment,
because it's reflecting
blue light here.
But when you get on
into in the near-infrared,
these are actually
due to vibrational transitions.
And there is an example
of vibrational transitions
at the bottom of the slide here.
So you get
vibrational transitions when you
absorb
light in the near infrared
or in the mid infrared, which
is even further out.
So this is an example
of a CH2 group in a molecule.
The absorption of light
can induce stretching
vibrations, which involve
a change in the bond length.
And you can also have bending
vibrations like down here
where they're involving a change
in the bond angle.
So these absorption features you
see here, this doublet around
2,300 nanometers,
are actually due to absorption
of the light and stretching
and bending modes
of the hydroxyl groups
in the azurite and also
the carbonate groups.
And then this absorption feature
you see here around 1,500
nanometers are actually
due to stretching modes
of your hydroxyl molecule.
So this is how knowing what
these absorption features are
due to, you can do material
identification.
So that's a bit
about spectroscopy.
So now we want to do
spectroscopic imaging.
So the equipment is a little
different than if we were just
to do multi-spectral imaging
where we have a detector
and then we put a filter
in front.
So also we have a detector.
And this time we're using
a spectrometer that has
a grading.
And this grading
takes
the incoming reflected light
and separates it
into the component wavelengths.
And this grading actually allows
a much finer spectral sampling.
So the width
of our spectral bands
is somewhere on the order
of three nanometers.
So rather
than with the multi-spectral
imaging, we're passing light
in 40 nanometer gaps,
we can use slightly different
equipment
and get finer spectral sampling.
So when you do that, what you
end up with
is this three-dimensional data
cube.
So two of your dimensions
are your spatial dimensions
of your artwork.
And then your third dimension
is your spectral dimension.
So again, this data cube
is a stack of images.
But rather than just 10 images
or so, like we had
with our multi-spectral system,
now we have a stack of hundreds
of images.
And they're much more closely
spaced together.
So, again, like what we did
with the multi-spectral system,
if you look at this pixel
in this blue region
of the Harlequin Musician
in his face and then you plot
in your first image
if you look at that same pixel
you can plot the average
reflected light intensity
in this spectral band.
But this time the spectral band
is very narrow it's about three
nanometers in width
as opposed to 40 nanometers
that we had with the filters
that we used
for our multi-spectral system.
And then what you can do
is you can drill
through your stack of images.
And you can plot how
the reflected light intensity
varies with wavelength.
And you can see, because we have
hundreds of spectral bands
and because they're very narrow,
our spectral sampling is much
higher.
And then this spectrum now
essentially looks continuous.
It's less connect the dots
like now, and it essentially
looks continuous.
So based on these absorption
features you see here
and here, this lets us know
that this paint contains
cobalt blue.
And because we have higher
spectral resolution,
we can actually,
you see these slight wiggles
in this absorption trough
here and right here?
Because we have the higher
spectral resolution,
we can actually start
identifying some
of these absorption features.
And so we can distinguish that.
So now this is a type of--
this is reflectance imaging
spectroscopy, which is a type
of hyperspectral imaging.
So now we're collecting hundreds
of images
as opposed to the 10 or 20
images we were getting
with multi-spectral imaging.
So again, you can look
at your data.
You can look at all the images
that you've collected.
Or you can look at the spectra
that you can extract
from your data cube.
So now we move on and talk
about how we use some
of this technology to look
at works of art.
So we have six examples we'll
talk about.
And I'll
talk about the first three
here and then hand it back over
to John.
And he'll walk
through the last few examples.
So as John showed before,
this is The Feast of the Gods.
So it was the Duke of Ferrara
commissioned this.
And Giovanni Bellini painted
this initial composition
with these trees spanned
the width of the canvas before.
And then the Duke commissioned
a couple of reworkings
of this painting.
And so ultimately Titian made
the last reworking where he
painted
this mountainous backdrop
that we see today.
So this is what this image looks
like in the near-infrared.
You can see this.
And there was a lot of work done
on this painting in the 80s
where they had taken
cross-sections, which are very,
very small components
of the paint,
so on a microscopic scale.
And so they took cross-sections,
and they identified a lot
of the pigments that were used
in the painting.
So there was a cross-section
taken from this existing hill
background here.
And so this is shown here
at the bottom.
And you can see, in some
of these lower layers, there's
this layer.
And you see some
of these blue particles.
And using microscopy, which
is when you're looking
at this paint
sample underneath a microscope,
they could identify that this
was azurite.
So these blue particles
are azurite.
And then this layer also
contained some lake pigment.
And then this was on top
of that layer
is this green glaze, which was
a copper resonate with azurite
and a red lake.
And then this final layer, what
we see
is
this brilliant green colored
layer.
So we knew that there was
azurite in some
of these intermediate layers
in this point on the hillside.
So we thought what else can we
learn
with these imaging spectroscopy
methods that we've talked about.
Can we bring
some additional information
to the table?
So here is
a false color infrared image.
So I've taken the spectral band
images
at the specific wavelengths
and placed them
into the red, green, and blue
color channel.
So you can see now--
so this is the region
between pan and this nymph
with the blue bowl.
And you can see here
the delineation
of this hillside.
You can see this hillside now
is appearing as this blue color.
And you can see if you look
closely, the brush strokes
that are associated
with this intermediate layer.
Because we know these brush
strokes--
these brushstrokes don't
correspond with what you see
on the surface.
So now we're seeing, which
is really pretty cool, the brush
strokes
of this intermediate hillside
layer.
And now if we look
at some spectra,
some reflectance spectra
from this region--
so just so you-- this blue bowl
is representing
like a Chinese porcelain.
And it has this blue painted
pattern on the surface.
So if we look at a spectrum
from this blue area,
this is what we get.
And so this is actually
indicative of the pigment
azurite.
So if you remember on the slides
before,
it had this strong absorption
doublet around 2,300 nanometers
that are related to the hydroxyl
and the carbonate groups.
And then it has an absorption
feature around 1,500 nanometers
related to the hydroxyl group.
So we know the blue pigment
on the bowl is azurite.
So now I wanted to look
at the pigment in this hillside
where we see these brushstrokes.
And you can see here
in this red spectrum here,
we see an absorption feature
at 1,500 nanometers that's very
similar.
This absorption doublet you see
here is actually due to the oil
paint.
Because this is painted
with oil.
So that's what these doublets
are due to.
But if you look here,
this feature looks--
this absorption feature looks
slightly more broadened.
Because I'm getting
some contribution from azurite.
And just for comparison, if you
look above the hillside
where there actually isn't
any azurite, you don't see
this absorption feature here.
And this feature, you can see,
looks a bit sharper.
So what's cool about this is
with the imaging now,
based on the spectra,
we know that this material here
in this hillside
contains azurite.
And now we're able to map
its distribution.
Because we can see this azurite.
We can see the layer that
contains azurite.
We can see these brush strokes.
So this is adding something.
Because before we just knew
there was
azurite
in a single cross-section taken.
But now we can actually map
the distribution
with the imaging spectroscopy.
And then we can identify what
this material is by looking
at the spectrum.
OK, so the next example,
this is a panel painting,
an early Renaissance panel
painting by Cosimo Tura.
And this is the Annunciation
with Saint Francis
and then Saint Louis
of Toulouse.
And so there's also a panel
of Mary here and then Gabriel.
So one of the things
that we can do, since we're
able to extract spectra
from our imaging cube,
and we can actually do material
identification.
So we have algorithms that we
can use to actually pull out
spectra that represent materials
in this image.
So that's what we've plotted
here.
And then we've created this map
here in the center.
So we know from the spectra,
we know,
like for example azurite,
this light blue spectrum is used
in the background in the sky.
We know that her blue robe is
ultramarine.
The red robe you see here
is actually an insect based
red lake.
So there's
insect base red lakes.
There's plant based red lakes.
So as John likes to say,
this is a non-vegan friendly.
And you can see, this is
the yellow,
the scatter distribution is
where there were paint losses.
So this is actually--
this material is due to cobalt
blue, which has a very
distinctive spectrum.
And you can see
its scattered distribution,
and that maps out nicely.
So one of the things that we
weren't quite
sure of with the reflectance
imaging spectroscopy
was the landscape.
So right here.
So the systematic catalog entry
for this painting
describes the landscape as being
this fantastic rocky landscape.
And based on the spectra,
we thought that this looks
similar to umber.
And umber is an iron oxide
with manganese oxide.
And this looks similar to, like,
reference spectra we have
of umbers.
So we thought, OK, if this is
umber, let's look for iron
and manganese.
So this is just, for an example,
a unit cell of an iron oxide.
And so this consists of atoms
of iron.
So we have another technique
that we used to look for iron
in manganese atoms that come
from a particular element.
And so that technique
is x-ray fluorescence.
And now we're talking
about using x-rays
as our excitation source.
So we're using energy that's
more energetic down here.
And so with x-ray fluorescence,
what you're doing
in this little diagram
of an atom, you're actually
using x-rays.
And they're energetic enough
that they kick out an electron
that's orbiting in one
of these inner shells.
And when that happens
you can get an electron
from an outer shell
to fall back down to take
its place.
And there's a difference
in energy between the inner
and the outer shell.
So when it does that,
this electron that's falling
back down to take its place
actually generates--
has to release some energy,
and it does that in the form
of a secondary x-ray.
And that's what we detect.
So the energy of that emission
is related to the element,
or the atom,
from which it came from.
So with x-ray fluorescence,
you end up with a spectrum that
looks like this.
It's a series of peaks.
This is
your x-ray fluorescence
intensity on your Y-axis
versus energy.
And so, like, for example
this peak here, resides
around 6.4 electron volts.
And so that's the energy where
if you have iron present,
you'll see a peak
in your spectrum at that point.
So you can get information
about what atoms are present
and they come from which
elements with x-ray
fluorescence.
And we can do x-ray fluorescence
imaging spectroscopy by raster
scanning our painting.
So we can-- we have
our excitation source
and our x-ray detector.
And then we can move
the painting and collect an XRef
spectrum point by point.
So that's how we build up
an XRef image.
So in this question about what
is the landscape,
we wanted to look for iron.
And so here's this map of iron
you see here.
But you can see in the region
of the background, I really
don't see a whole lot of iron.
However, when you look
at the copper map,
you're actually seeing a lot
of iron in the background.
We know there's-- excuse me,
a lot of copper
in the background.
And we know there's copper
in the sky,
because there's azurite there.
But then we see copper
in the background.
And some of the intensity
differences you're seeing
in this copper map are mimicking
the types of shadowing you're
seeing in the visible.
So this really clued us
into the fact
that this is actually a copper
containing pigment
in the background.
So rather than being
this fantastic rocky landscape,
this was likely actually green
at some point.
And so this really isn't
that this was probably a copper
resonate that's degraded.
And with the panel of Mary
here, here's a false color image
from the near-infrared.
And from an image like this,
you can kind of start seeing
some of the under drawing that's
used.
And you can kind of see some
of the hatching that's used
for shading and modeling
of the robe.
And when you look at spectra
from--
if you look at a spectrum that's
collected over one of these
under drawing lines,
it looks like this.
And this is from a region
free of restoration that was
just over the blue robe,
not over an under drawing line.
So you can see there's
a relative difference
in reflected light intensity.
But this region here is also
a little more absorbing here as
opposed to this.
So we thought based
on the spectra here,
we thought maybe the
under drawing was an umber.
So what we can do
is look at this spectrum here
taken from over one of these
under drawing lines.
And we can use an algorithm
to actually find the degree
of match between this spectrum
and all the pixels in our image.
And when you do that,
you get something like this.
So this is this map.
We're in this map,
we think the dark lines are
actually
corresponding to original
under drawing.
So you can see some
of this hatching and shading
used here.
And in this region,
we know there's some restoration
in this region of the folds
here.
We can actually see below that
now and see what some
of these presumably original
under drawing lines looked like.
So if we jump forward
a few hundred years
and talk
about abstract expressionism,
we'll talk about Jackson
Pollock.
And so we had imaged a section
of Lavender Mist, which
is in the collection
of the gallery.
And Jackson Pollock, he's
probably most well known
for these drip paintings
like this.
And the way he created those is
he would lay the canvas
on the floor.
And then he would fling paint
onto the canvas with brushes
or with sticks.
So it was a very physical
process.
So he used paints that had
different binding media.
So that's what is of interest
in this discussion here.
So, for example, so here's
Lavender Mist on her easel.
Here's a reference spectrum
of oil and here is a reference
spectrum of alkyd resin.
So with oil, this is just
shorthand notation.
These long chains you see here
are hydrocarbon chains where
there's carbons and then there's
hydrogens coming off of them.
And that gives rise
to some absorption features
from the CH2 two groups
in these hydrocarbon chains.
So you get this doublet right
here that's due to stretching
and bending vibrations
of the CH2 groups.
And then you also have
an absorption feature here to do
stretching of the CH2 groups.
So with alkyd resin, it's an oil
modified polyester.
So it has some hydrocarbon
chains you can see here.
So it shares some
of the same spectral features
as oil.
So it's got an absorption
doublet here, this doublet here.
But it also has
some additional spectral
features related
to this aromatic ring structure
that you see here.
So you can get stretching
due to the aromatic CC and CH
stretching that gives rise
to this more intense absorption
right here.
And then you also
see this shoulder that appears
at lower wave numbers
relative to the oil.
So when we look at a couple
of different white pigments
in this painting,
here's one white pigment.
And it looks very
similar to the spectrum of oil.
If we look
at another white pigment,
you can see this absorption
feature here.
You can see the shoulder
appearing here.
This looks more
like our reference spectra
of alkyd resin.
So one thing that we did,
the difference is when you look
at the reflectance spectra
are relatively
subtle between these.
You see the shoulder.
But if you actually calculate
the first derivative
with respect to wavelength,
these differences you see
in reflectance
become accentuated.
So this shoulder here that you
see actually
becomes like another peak
in your first derivative
spectra.
So we actually used
the first derivative spectra
to actually make material maps
of the binding media.
So here is this
about a square meter
of the region that we imaged.
Here's this map.
This maps to oil.
So you can see that you have
these--
this maps to more or less like
these white skeins of paint that
are more or less straight.
And they're kind
of like these tadpole shapes
where you have probably
him squeezing paint
from a tube where this is
the initial squeeze that results
in this head of the tadpole
and then this extended squeeze
that results in this long tail.
Here's the map that we get
for alkyd.
It maps to color--
paint of different colors
so there's
white and blue and different
colors.
But you can see some
of these paint strokes are more
curved,
which suggest that the paint is
more fluid.
And you can see
that its distribution is more
scattered.
So it's
likely underneath other layers
of paint.
And this is something that looks
kind of like a mixture
or layering of the two.
If you look just at this detail
here,
you can see this white stroke
and this white stroke
look very similar by eye.
But this one is actually oil.
And some of these other strokes
like here actually map to alkyd.
So using
the spectral properties,
we can actually distinguish
between different binding media
that he used.
So with that, I'll turn it back
over to John.
And he can walk through the rest
of these examples.
JOHN DELANEY: All right,
so we're going to go back
in time.
And we're going to talk about
a choir book basically that was
constructed in Florence
and was constructed by two
different groups.
One was a workshop by Pacino
and the other one was a workshop
by the Master of Dominican
Effigies.
We don't know anything more
about him than that.
So we're looking at something
in around 1340-ish time frame.
Now these laudario choir books
were relatively large
and were commissioned
by wealthy tradespeople
in Florence.
They were put together,
and they would have celebrations
for different parts of the year.
And they would be taken around
to different places
or holy sites
and these tradesmen would go
and chant.
And this would be carried
by a priest.
Now this would not be tied
to a specific church.
But it's tied very closely
to these wealthy groups who had
them painted.
And, of course, they
went for the best materials
and put out the best money
so this would be only
of the highest quality.
Now, of this particularly
laudario, there are only about
28 leaves that remain.
There were probably 120 to begin
with.
And they're done-- they're
basically written
in the Italian vernacular
and not in Latin.
So actually the tradespeople,
or the people that had them
created, could actually follow
along and read them.
When Napoleon came into Italy,
he essentially disbanded
and shut down the Church.
And these pages and books were
sort of scattered.
And some of them sort of
got caught and then migrated
to different parts of the world.
We have some of the collection
here at the gallery,
although the book still remain--
some of the books still remain
in Europe.
This particular book was
completely disassembled.
So we have three pages here
that we're
interested in studying.
One of them in particular
is this one attributed
to Pacino, which is involving
Christ with the apostles.
So Christ in Majesty
with the apostles around,
we talked about it earlier
briefly.
Now this is another cutting
here.
This is an illumination
by the Master of the Dominican
Effigies.
And you actually can see not
only the inner portion but all
of the marginalia
and the writing around it.
Now that's not even a full page.
A full page would look
like this.
So you can see that this has
been even trimmed down further.
Now one of the things we wanted
to do was to study the materials
used in all
of these illuminations
that we have, these cuttings.
And our colleagues at The Getty
study theirs as well to see
if we can learn
about the working methods
of these two
different workshops.
So this is a set up here showing
a hyperspectral reflectance
camera that we built here
at the gallery with a grant
from the National Science
Foundation and the illumination
under examination.
And we collected 750 images
to collect a spectral database
to interrogate.
And from that, we pulled out
the reflectance spectra
of blues.
And you can see there are
essentially three
different blues here.
We know the blue
of the high reflectance here.
But there's a shoulder
and these features here.
And as Kate indicated earlier,
it's not a surprise that this is
azurite and up here
is natural ultramarine.
And this is something
in between ultramarine layered
on azurite.
Azurite is a very cheap pigment.
Ultramarine is a very expensive
pigment.
So having this data,
we can go back and interrogate
the data sets with the data cube
and make a map
and find out where
these illuminators decided
to use the azurite
and the ultramarine.
And you notice that the azurite
is used extensively
throughout the blue regions
of the illumination.
But right around Christ,
we see the reddish color where
there is natural ultramarine
right on top.
And actually on his white robe
is where we find this very
precious ultramarine, right
around Christ.
It makes sense.
It is interesting that's also
found around here on John.
But that's probably
another story.
One of the questions that came
up in the analysis was,
since our page is cut down,
we just have
the central illumination and not
the writing around it,
is where does it
go in the laudario?
Where in the book does it go?
And it would be really nice
if we had some writing.
I kind of skipped over this.
But our cutting is not only cut
down so there's no writing
around it, it got mounted
onto a board.
So we can't see what's
on the back.
And on the back there should be
some writing and music.
So it's been postulated that it
could be the frontispiece.
It could be at the end
of the book.
There are various places where
people think it could be.
Without the additional
information accompanying text,
the placement of the books
is uncertain.
So we thought maybe we could try
to get at this by using
our special imaging methods.
And just to give you a scale
of the size of these books,
they have to be read by people
without glasses from a bit
of a distance.
So they are relatively huge.
While we noticed
in the infrared images,
the false color infrared images
taken, that we could start
to see some text.
That was pretty exciting.
So doing a little bit of math,
in this case principal component
analysis, we were pretty
excited.
Because we could start
to actually see letters.
So, OK, this is great.
We're going to send this off
to the people who can read
Latin and early Italian.
And they're going to tell us
what it is.
And bang, everything's fine.
We sent the images off.
And they sent us an email back
saying, really exciting.
Could you get a bigger, better
image?
So, well OK.
What's happening here
is the light scattering
by the paper is obviously
limiting the readability.
Because the lights going
through the paper
and then reflecting back off
the white background and out.
So we said, OK, why don't we
scan this
with our atomic elemental
scanning system.
This is the set up here.
And our hypothesis
is these hymns are written
in iron gall ink.
Notice the word iron.
For me as a physicist,
we should be looking for iron
and then maybe some
the trace elements like zinc.
So we'll go do some mapping.
And about, I don't know, three
days later, we started to get
these maps.
Here's a map of iron.
Doesn't show any writing.
Here's a map of zinc.
It doesn't show any writing.
It matches the azurite.
And zinc is not in azurite.
It's actually a trace element.
And that tells us a little bit
about the mine where it comes
from.
But it's not answering
the question.
If we look at mercury, which
is related to vermilion, which
is a pigment obviously used
for vermilion,
we can see the music lines
on the back.
But we also see this little bit
of a design here, which was kind
of exciting.
Because that design, when you
look at it--
we actually took an image
with an x-ray set up, we can
actually see at low voltages,
the design pattern, which I
colored in,
in Photoshop using the tools
that my daughter taught me how
to use.
And you can see this design is
pretty intricate.
And you see these at the starts
of sections of words.
So we know there should be
wording across here.
We've seen the wording
in the infrared.
But in the hyperspectral,
we're just not reading it.
So then we had another idea.
What if we flip it over and read
it from the back.
And it worked.
So now we're actually--
and this is lead of all things,
we're actually seeing in lead
we're seeing the contrast
to make out some letters.
And they're sharp and they're
clear.
And this, thank God the art
historians said they could read.
That's what it translates to
in early Italian.
This is kind of what it means
in English.
The word made flesh, which holds
up the ceiling, alter with--
so it's a beginning
of information.
The good news is this fragment
of chant is written
in Italian vernacular
and not in Latin.
So that means is definitely part
of such a choir book.
And it kind of suggests
that it's coming
from near the end of the book.
But we really would like to have
some more of his text.
Because anybody who reads
Latin knows that context
matters.
And we need a few more words.
So we have some more image
processing to do.
So we'll turn back now
to this particular painting
that's fascinated me
for a long time,
this blue period painting
by Picasso of Le Gourmet
and this picture of the woman
underneath, and again, as we
mentioned earlier,
this particular what appears
to be a drawing of a woman
underneath is very intriguing.
But the question is, is it
related to a finished painting?
Or is it even by Picasso
and when did he do it?
And that just begs more
information.
With a hyperspectral imaging,
we can go from this to a more
isolated image of the woman,
which is a lot clearer to see.
And we begin to notice that she
has a necklace, which
is interesting.
Because as I understand it,
Picasso did not use much jewelry
when he did painting,
or he did not paint people
with jewelry, I should say.
So we said, OK, let's
try to look at this
with the elemental scanning
system.
We know that from the x-ray,
there are
some x-ray absorbing material,
probably lead, lead white.
Quite a bit of it because it's
very hard to see the face.
So let's scan for lead.
There they are.
Lead alpha line and alpha
and beta.
And we don't see the woman.
And this actually has to do
with the fact
that there's actually zinc
white on top, which
is preventing seeing the lead.
So we kind of ran into a wall.
But then we went back
to the hyperspectral data set
and said,
well, what if we measure
the depth of the hydroxyl ban
that
is
characteristic of hydroserocide
in this case,
lead white with the presence
of the hydroxyl bands.
And when we do that,
we get this image.
And I think I can probably
convince everybody
in the audience this looks
like a painting.
This looks more three
dimensional.
And you can see this cross
is showing up,
which tells us this is a woman
with a mantilla who
is either going to or coming
from mass.
So that's a lot more
information.
What we did get out
of the elemental scanning
was the presence of chrome.
And that chrome maps into places
on the final composition.
But that necklace we talked
about and a little bit
associated with the cross,
well, that would be very
convenient if that was chrome
yellow.
Unfortunately, with elemental
imaging, we don't--
we get some of the atoms.
We don't get enough to tell us
the pigment.
But we can infer it.
So chrome yellow makes sense.
And then we spoke to a curator,
an art historian in Barcelona,
who made us
aware of this particular
painting by Picasso.
Happens to be 1901, very similar
to the dating of the blue period
painting that we of the La
Gourmet.
So if you'll take some license
by a bunch of scientists
with some Photoshop minimal
skills, maybe we're looking
at something like this.
OK?
So it's not drawn, it's painted.
We know where it goes.
And this apparently shifts
the date of our painting
a little bit.
Well, this is the last example
we'll give you.
It's kind of an exciting example
because at the end,
you'll see there's a show coming
up related
to this particular subject.
This is a painting by Fragonard.
It's associated with the Fantasy
series.
These are a series of paintings
that you'll see in a moment that
were only associated together
by grouping them by their style
and not by anything else.
And it's a beautiful picture
of a woman reading of this book.
It's a very quiet scene.
And it's a favorite
in the gallery.
Now if you look
at these paintings that are
in the Fantasy series, for sure,
you notice there is
a distinct difference
between these two sets
of compositions.
All of these
are in fancy costume,
Spanish costume.
Well, she is too.
But they're all sort of engaging
the audience somehow.
They're all looking out.
There not in the sort
of quiet view.
They look more like portraits.
And this has always been sort
of an issue with this painting
in terms of how it relates
to this group that
is notionally, again,
associated with these Fantasy
figures based on the style.
So we were asked to look at-- we
look at some of the clues
that people had noticed
over the years.
One was, if you start to look
behind the woman's hair,
there's something going on here,
this sort of gray paint.
And there's
a faint characterization
of some sort of clouted material
here, maybe a feather.
And if you equalize
the histogram,
if you take the image
and stretch it and make
sure each gray level or color
level has its own level
of importance,
you can see clearly he painted
out what is essentially
a feather not unlike some
of the feathers we saw and had
the hair of some
of the other members
of the Fantasy figures.
So that's one clue, sort
of a pentimento.
The other clue is the x-ray.
The x-ray shows a second head.
An earlier version
of this painting with a person
looking out at us.
That's certainly much more
convincing.
And this is a close up
of the same thing.
The challenge with such images
that they tell you something
about where the person is
sitting prior
and where they're looking,
it's really hard to find gender
on the basis of this or age.
It's just the nature of x-rays.
So we were asked to see if we
could do a little more to pin it
down.
So how did the figure really
look?
Well, we did
the hyperspectral imaging scans
and made a false color image.
And now you start to look here.
And maybe we'll take a minute
to stare.
You see the woman's face
and profile disappearing.
You can see the lips of a woman
underneath.
You can see she has a black tie
around her neck.
That straightens out the gender.
And you can see her forehead.
And you can see one eye
and a little bit
of the other eye.
We do have a lot
of other material
that's absorbing in the IR
making it hard to see the rest.
But the only change that's been
made in this composition,
except for someone doing that,
is essentially that of the face.
So it's definitely a woman,
and she's looking out
to the group.
But we have
the elemental information
that we can get by x-ray.
For us this was sort of flesh
this out to get more information
about the pigments
and maybe get a better idea
of how to reconstruct
the earlier picture.
But we can look at lead.
And you can clearly see more
of the figure.
She looks rather old here,
doesn't she?
She looks rather young here.
We can look at the iron, which
gives us more information
about this extension
or whatever was a costume part
attached to her hair.
And then we can look
at the vermilion map, which
is basically associated then
through the mercury.
And now you can see the ear
that we can't see
in hyperspectral imaging.
And you can see she has red
in her hair so maybe she was
a redhead.
And then, of course, we have
this piece of information.
So now we have enough pieces
of information to give it
to back to the conservators,
especially someone inclined
to actually do some simulation
in painting.
And also we have the collection
of other Fantasy figures
to draw from to understand
things like possibly
these little dots here of color,
which were probably jewels
and along with this feather.
And when you do that,
that's what you end up with.
So we went from possibly a guy
to this, a woman who fits in
with the series.
And it makes a much more
compelling story.
There's more to this story.
If you come to the exhibit,
you'll learn a lot more
about how these are more closely
related.
We did extensive studies
on a whole series
of these Fantasy figure
characters.
These will be in the show.
And there's a drawing that
popped up that sort of links
some of these together.
And that brings us to the end
of our talk today,
which we have thoroughly
enjoyed.
And there are a lot of people
to thank.
We would really like to thank
our colleagues.
This work is not done
without working closely
with conservators and curators
who come up with ideas,
help direct the research,
and actually tell us what we're
looking at since we're also
scientists and also
our colleagues
in the scientific group
here at the gallery who are
first rate who know
a lot about different pieces
of information
that can help ensure that we're
moving in the right direction
as we develop
these new techniques.
And we're indebted to a lot
of different funding
foundations, Samuel Kress,
the Mellon Foundation as well as
the gallery and the National
Science Foundation.
So with that we close, and thank
you very much.
