>>Welcome to what I gather
is the last of this seasons
>>Thank you
>>[laughter] The last
of this seasons set
of UCL lunchtime lectures.
I gather they will be
restarting October.
But today's lecture is on
pigments in art and archaeology
by Professor Robin Clark.
Now Dr. Clark has, sorry,
Professor Clark has led a long
distinguished scientific career.
He was born in New Zealand
and has been a companion
of the New Zealand Order
of Merit since 2004.
After taking his first
in Master's degrees
at Canterbury University College
in Christchurch, he first came
to the UK in 1958 to undertake
studies for his PHD in Chemistry
at UCL and he's remained
at UCL ever since,
although he has managed
to fit in lecturing
at over 350 other universities
and institutions in that time
and also acting as
visiting professor
to 13 other universities.
Besides all this he is a fellow
of many major institutions
including the Royal Societies
both of this country and
New Zealand and he served
on the councils of the Royal
Society, the Royal Institution,
where he was sat to
retrieve 36 years
at the University
of London Senate.
He has received awards
too numerous to go into.
Although he's now
officially retired he has
in no way slowed down, as
this lecture will show.
Professor Clark has
long been interested
in molecular spectroscopy.
In 1969 he brought the first
laser Raman spectrometer to UCL
and he's been heavy involved
in the development
of this technique.
Raman is now something which
is very widely used throughout
industry and chemistry
but much more importantly
to all right minded people it's
used extensively in museums.
We have had a Raman spectrometry
in this museum now since 1999
and you'll see examples of some
of the work that we've done
with it in the Treasure's
of Heaven exhibition
which is opened at the moment
in the round reading room
and also spectra in the, along
with some of the Chinese Jades.
Professor Clark, who is a
pioneer of the introduction
of this technique into
art and archeology
and that's what he's going to
be talking about to us today.
So with that I'd like to
introduce Professor Clark
to talk about science meet
art, investigating pigments
in art and archeology.
[applause]
>>Good afternoon, everyone.
When you look at a piece of
medieval artwork such as this
with intertwined figures, great
design, strikingly colored,
you always admire it
as a piece of artwork.
I want to try and convince you
that it's also excellent
science behind all of that
because when you think about
it all the colors are pigments.
The pigments, for
most periods of time,
were inorganic pigments,
minerals
or synthetic inorganic
materials.
And so you did need to
know chemistry in order
to be an artist and the early
artist didn't know a lot
of chemistry.
They knew that in many
cases if you put A next
to B they would react
and so they didn't do it.
So they had to know chemistry.
So I want to try
and persuade you
that this is a branch
of chemistry.
So what is the purpose, and
pigments are the key to it,
so what are the purposes
of looking
at pigments and identifying
them?
Well the characterization, what
pigments did an artist use?
Did he use a single one
or a mixture and all sorts
of questions of that
sort, questions to do
with restoration,
repair of damaged areas,
have there been any
changes in color with time,
anything to do with
conservation.
What are the effects of heat,
light and gaseous
pollutants and such like?
And the next question of
authentication which is linked
into the assignment of a
probable date to a work of art.
So what are these pigments?
Well there are several hundred
of them, increasingly fast now.
It isn't possible to go through
all of these but just by way
of illustration I've just listed
up the seven most common
blue pigments used and also
at least 20 others in
widespread use which are blue.
But this is the sort
of information
which is readily now available.
We know what the chemical
name is, the formula.
We know the origin of the
blue color in each case.
It's different for different
pigments and that's a branch
of inorganic and
physical chemistry
that was heavily studied in the
1950's and 60's and 70's to find
out from where the electron was
going and to where it was going
in the molecule and it was
always going to be in the red,
absorbing wise, if
the thing is blue.
So we know all about
the origin of the color
and this column simply lists
whether something is a mineral
or whether it is synthetic.
And if it's synthetic I've
listed the year of manufacture,
fashion blue here, 1704.
Copper [inaudible] blue to 1936
so the message I want to get
over is that if you find
Egyptian blue on an Egyptian
from Paris supposedly dating
to 1250 B.C. that's bad
news for the proprietors.
Now the technique I'm talking
about is something known
as Raman scattering.
Now you may or may not wish to
know about this but you're going
to get one slide anyway.
It goes back to Lord Rayleigh
who in 1870 was the first person
to realize that if he took a
beam of light of one color,
one frequency, and shot
it, he was interested
in gases, it would interact.
Most of the light goes straight
through cause it misses
the molecules but some
of it strikes the molecules
and the molecules reradiate the
same frequency in all direction.
It's a very weak affect
and it happens to relate
to the fourth power
of the frequency
that you used in
the first place.
That means blue scatters
better than red.
Now we're all well
conscious of that
because it is rays scattering
from molecules in the sky
which makes the sky blue,
molecules of oxygen and nitrogen
and what have you, they
scatter much more effectively
in the blue and they
scatter in all directions
to make the sky blue so that
when the sun sets it doesn't
all go black instantaneously.
So ray scattering is
well known but it's not
in the molecular
sense very useful.
We had to wait until 1928
and to C.D. Raman in Calcutta
who made the key discovery
that it wasn't just
the original frequency
that a molecule scattered, it's
the original frequency plus
or minus some other frequency
related to the molecule.
And in fact what I'm
going to be talking
about is what's called the
Vibrational Raman Effect.
That is you see plus or
minus little sidebands.
You've got the Rayleigh line
here and then in pairs going
out you see these some
difference frequencies
which relate to the
vibrations of the molecule,
so highly specific to the
molecule they really do act
as fingerprints of
what you've hit.
So I can shoot this beam
that anyone's top over here,
I won't do it but this
man's pretty blue top there
and the signal will come back
telling me exactly what pigments
he's got in that.
I mean I haven't got
the detecting system
and that's what's tricky
but that's the basis of it.
How do you do it?
Well in Raman's day he
actually used sunlight,
which is not monochromatic,
not single frequency
and as his detector
he used his eyes.
Well this was a proof of
principle experiment he did.
To do it he quantitative, you've
got to have single frequencies
and you've got to have
a really good source,
a high power densely source
in watts per square meter.
And of course we've gone from
the eye to photographic plates
to all sorts of lasers
and things
and increased the power density
by many orders of magnitude.
And then in terms of
detectors for the use
of the eye is extremely
limited and we've gone
to many other sorts of
detectors finally to something,
which is shown here,
is a CCD detector.
That means charged coupled
device, something designed
by physicist in order to see
stars in distant galaxies
and that will give you an idea
of the fantastic sensitivity
that is on the modern
Raman detector.
So this is the sort
of system that much
of what I will talk
about looks like.
The laser beam comes in the
back of this instrument,
shoots along here, is filtered
so there's only one
frequency comes here.
We link it to a microscope so
it's then deflected down there
to the stage and that's
where you put the sample.
It then scatters back up here,
comes right through this optical
system into this CCD detector
which then tells you what these
summon difference frequencies
are and you then go to a library
of Raman spectra which we
and other people have developed
so that this can all be
looked at and identified.
Well we first looked at
anything artistic sort of 15
or more years ago when somebody
brought us a little thing
of this sort here.
This is a historiated letter
R, which you can see here.
Here's the R, historiated means
there's a story being told
in the middle of the letter R
and the letter R
is the first letter
of the first word on a page.
And the question was,
I mean this was obviously the
Archangel Gabrielle bringing
good news to Mary
but the question
that we had was what were
these two blues here?
That's what the library
wanted an answer to.
And we could tell very quickly
that it was the same
pigment azurite,
a copper based carbonate.
And the difference in depth
of color simply related
to particle size.
The pale is 3 micrometer
sized grains
and the deep blue is 30
micrometer sized grains.
And then we could run
through and we looked at these
as malachite, that's basic white
lead, basic lead carbonate.
This is vermilion,
mercury sulfide
and the yellow is
a lead II yellow.
We also looked at the
black and that's revealing
in some interesting way
because we had assumed
that that would be carbon
black, a single material
but in fact it's actually a
mixture of different pigments,
each one of which absorbs
light in a different frequency
through the visible so you get
the net effect of being black
by having this mixture.
I don't know why someone
would do that but that's what
in fact they have done
in this particular case.
And this also shows the benefit
of coupling the Raman system
in with a microscope because
you can look at these,
this is obviously a pigment
mixture, and you can move
across you see and come
onto every pigment grain
and tell what each component is.
And the spatial resolution
is about 1 micrometer,
that's 1 millionth of a meter.
So you can go onto that yellow
grey [inaudible] which is
about 2 micrometers across,
get the signal back from that
and it's not interfered with
by all the other pigments
around about.
It's a very good, that what
we mean by spatial resolution,
the laser beam will focus under
each pigment grain in turn
and you can find out
what each component is.
Most techniques won't go
anywhere near doing that.
The Raman spectra themselves
look something like this
and this is another very
early one that we looked at,
a Paris bible coming from
the Czech Republic, in fact.
Here we have azurite
[inaudible], lapis lazuli,
realgar, lead white, red
lead, malachite and vermilion.
That's eight different
very common pigments
and as you see each of these
is what we would call a Raman
Spectrum, that is a
listing, a sort of scanning
of all frequency differences.
And so if you see down here the
Rayleigh line is somewhere near
the edge here.
It's been cut off the figure
because the ray is a much more
effective scattering business
than Raman is so you don't want
to go take the detector anywhere
near the Rayleigh line otherwise
you're liable to
kill the detector.
So coming up quite
close to zero,
actual zero would be the
Rayleigh line except we've cut
it off from there.
These are the peaks,
the difference peaks.
I'm not showing the sun but they
come out as I said like this
in pairs and these
are characteristic
of the compound you're
looking at.
So there's eight pigments there.
Everyone of these spectra is
different from every other one.
They're easy to get and so
they define what the pigment is
uniquely and quickly and they do
it with great spatial resolution
and so on and it can
be done [inaudible].
Of course you can also
look at pigment grains
if someone can bring those
to you but sometimes you have
to look [inaudible]
and you can do
that under this microscope
system.
Well many of the pigments
have several books written
about them.
I mean this is a big
and an old business,
writing about pigments.
I actually, long before
paying any attention
to artwork I was intrigued
with lazurite, 40 years ago,
wondering why it was blue.
Well this is the
mineral, lapis lazuli,
which comes from a very
remote part of Afghanistan,
in the hills and
that's the mineral.
The blue part is
what's known as lazurite
which is the intriguing part,
which is extremely valuable.
It's worth more weight
for weight than gold
in the Middle Ages because of
the brilliance of the blue color
and the permanence of
it and its stability
up to high temperature.
The rest is calcite
or something like that
and then there are flecks
of iron pyrites in there,
slightly brownish, and there
are a few other trace impurities
in it.
The whole history here related
to the very difficult
extraction business to get hold
of the mineral lazurite
after lapis lazuli.
There was not enough Lazurite
in the world for the artists
and that's why it
was so highly priced.
And the French government
offered a prize in 1824
to anyone who could make it.
People knew it was a
sodium aluminosilicate,
which is only one step removed
from [inaudible], which is known
and prized because it's white
and you make China Clay it is.
So they knew essentially what it
was, at least 99%, 99 1/2% of it
and there's a little
bit of sulfur there.
Well that's the bit that
intrigued me 40 years ago,
sulfur is obviously yellow
so it isn't sulfur itself.
And after quite a lot of
research, which I won't go into,
we turned out that
the chromophore,
that is the thing that's
trapped in the cubic cage
of lazurite is S3-, it's a SSS.
It's a bent sulfur species,
trinuclear species carrying one
negative charge and it's found
in a few other places, well in
crystals and sometimes in melts
when you melt potassium
thiocyanate.
So we know what that's
caused by and if you go
into the business you
can actually make it.
That's the synthetic
form which is low
and it's ultramarine blue.
There is also ultramarine
green, violet,
pink and an ultramarine
selenium,
when you get other radicals
trapped in the lattice.
So all of that is
now known about.
The ultramarine blue was made
in whole for well over a century
and have now sold out
to the French actually.
It was a big business
when I was a boy I know
because you didn't have
proper washing machines then,
you had a copper.
And the clothing that went into
the copper always had dolly blue
or reckitt's blue in it
and that's a little muslin
bag containing precisely that,
the synthetic form of lazurite
and they made tons and tons
and tons of it and it's just
[inaudible] and got entailed
in the fabric by a
complimentary optical affect.
The yellowing of the
whites, that was complimented
by the blue of the
ultramarine blue, dolly blue.
They may still put that in
some washing powders actually.
I'm not sure now.
Now I don't want to develop
onto stories about the pigments
but there are vast volumes
on all of the pigments.
Let me turn to some of the
things that we've looked
at in recent years so
that I know what we've,
so you know something
about what we've looked at.
The Lindisfarne gospels, did
I just check the time, yes,
okay the Lindisfarne Gospels
at the British Library,
this wonderful bit of artwork
made by Bishop Eadfrith in honor
of St. Cuthbert on Holy Island,
Lindisfarne Island, back in 715.
A fantastic piece of work.
It took him six years to do it
and it's absolutely
brilliant artwork.
You can see it yourself if you
wander in on the ground floor
of the British Library.
This is Eadfrith's
copy that he made.
It was a copy of the Saint
Gerome's version of the gospels.
And this is actually
the prefatory page.
And I'm no Latin scholar
but with my handheld
I can read two words
and it says n-o-v-u-m
o-p-u-s, new work.
I can't go beyond that but
there are plenty of experts
who will take you
well beyond that.
I just want to emphasize that
this is a wonderful piece
of artwork, brilliantly colored
and there are many
curiosities about it.
It was translated also from
the Latin into Old English,
240 years after this, 715,
and there you can see the
translation written here that's
known as interlinear gloss,
interlinear, between the lines,
gloss means translation.
I think it was controversial
when that was added
but it probably isn't now,
probably regarded
as interesting.
So this is the Matthew,
Mark, Luke and John
and again it's brilliant
artwork.
We had a look about it
at the British Library
and I'm not going to go through
all the pigments that we found
but I was more interested
in the one
that we didn't find cause the
British Library at the label
up in some detail about
lazurite and showing
where it comes from
and everything.
That was the only pigment
they mentioned on the card
in front of the actual bible.
Actually that's the only pigment
that is not there [laughter]
and when we looked at it it
was quite clear immediately
that this was indigo,
which you extract from woad
and it's a well known and grown
and has been for 1,000 years
or so in England, especially
on the Eastern side.
What was there was
definitely lazurite, I'm sorry,
it was definitely Indigo.
It was not lazurite.
And when you come to think
about it it was going
to be incredibly difficult
to get a hold of lazurite,
I mean did the monks
really know it existed?
How would they have gotten it
from the Hindu Kush Mountains
up to Northumbria in 715?
It beggars belief
so that's the sort
of strange information
found there.
We looked at the Tours Gospel,
825 A.D. Now this is
actually the cover.
It's an oak cover.
It's got an embossed
silver front to it.
It's got enamel in the
corners and it's got gemstones,
12 of them, all around
the outside.
The interest there is in
what the gemstones were
because it was realized that in
past centuries there'd been some
light fingered inspectors
and lookers at the gemstones.
We brought in a pocketful
of colored glass and sort
of substituted the
gemstone with colored glass.
They didn't know
what happened here,
well we still don't really
know but we looked at those.
There are only four different
stones there, there's amethyst,
emerald, iron garnet
and sapphire.
They are still there.
Whether they were the
original ones we don't know
but at least there's a
marker now if anyone wants
to substitute those
for colored glass.
We've actually looked at
eight Gutenberg bibles,
or pigments from them.
These bibles also on
view and very easy to see
at the British Library.
Guttenberg ran these,
the first one in Europe,
to use movable and
reusable type.
He made about 180,
about 48 survived
and there were [inaudible]
pigments to illuminate this
with because Gutenberg ran
off as it were the black
and white copy you
brought back from him.
If you wanted it illuminated you
had to find yourself an artist
and then he wanted payment for
all the pigments so you had
to decide whether you wanted to
put the most expensive of all,
Lazurite, on it or not.
For this particular one, the one
we studied in greatest detail,
also you could see in
the British Library,
is the George III copy
which went in about 1828
and it's superbly illuminated.
It's got images of
foliage, flowers,
birds and fruit crawling around
the main body of the columns,
which you can see here.
I mean this is absolutely
brilliant artwork.
Well we have looked at that and
of course these are big volumes,
I mean they're 25
million pound jobs.
You've got to be very careful
with them and you've can't sort
of try to bend the
back open a big more
to get it under a microscope.
You have to design the
right sort of equipment
which will hold it
at an optimum angle
and then use a mobile Raman
spectrometer, such as this here,
and that's a laser which
shoots down onto the page
and then you collect
the light back from that
and that tells you what
pigments are actually used.
Well this is what we found
on that particular one.
We've looked at eight of
them from different parts
of the world and there are at
least two others in the UK,
one at Easton College
and one at Lambeth Palace
and we've seen the
pigments from them too.
So we're still working
on this trying
to compare whether the palette
used was always the same
from one Guttenberg
bible to another.
You can also look at paintings,
I mean water paintings
quite easy to look at.
Ones that might have any
varnish on them are much harder
because the varnish fluoresces
and that's completing technique
but one did turn up in
London in 1995 and I can't go
into all the history of
this because it's big
but Vermeer's had
particular problems with them
because in 1947 someone was
convicted of forgery in Holland
who apparently made
about seven Vermeer's
which the experts
couldn't identify
and thought they were
Vermeer's so any Vermeer
which didn't have an absolutely
perfect history to it,
such as the ones that have
been in museums or libraries
since the year or in
Buckingham Palace or wherever,
there's no problem
with those but one's
where there's a little
gap in the knowledge
about where they were held,
anything of that sort had a bit
of trouble after
1947 and this was one
that came up in that category.
And Libby Sheldon, UCL History
of Art, looked carefully at that
for many years with some of
her assistance and we had it
at one stage just
to look at too.
And this shows that
Vermeer under the microscope
of the Raman microscope
and easily you could see how
one could track ground there
and see what pigments are.
There're actually only
two which really matter
which are lead-tin yellow
type 1 and lazurite,
which are consistent
with its being a Vermeer.
This is one of the problems
in this kind of work,
if you find something
that shouldn't be there,
that rules it out instantly.
If you find things
that should be there,
well okay, that's fine.
It doesn't prove anything
but you've then got
to do a whole host
of other measurements
to see whether you
can establish it
as it were beyond
reasonable doubt.
Postage stamps are
another form of artwork.
[noise]
There was one, we've
looked at Mauritius stamps
and these Hawaiian ones.
The Mauritius ones two
days ago in the Times,
there was a photograph
of an 1847 Queen Victoria head
blue [inaudible] stamp that went
for over a million
pounds so you do realize
that postage stamps are
worth an awful lot of money
if they're rare and it's
worthwhile trying to forge
if you're any good at it.
Well the Hawaiian missionary
ones were in that category,
1851, and there was
a group known
as the Grenelle Missionary
Stamps which were judged
in 1918, 43 of them were sold,
were judged to be forgeries.
Fifty five turned up
again in 2002 in London
at the Royal Philatelic Society
and we linked in with them
to have a look to see
what we could see.
Could we see any defining
feature which might show
that they are, that's the
stamp that was photographed
in the Times two days ago
that went for over a million.
This is the Hawaiian
Missionary stamp
that we looked at
with some care.
It's a .13 stamp shown here.
The blue is Prussian
Blue and then many
of the other colors are to do
with the Franking, the reds,
vermilion and hematite and
there's carbon black there also
and there's nothing
wrong with that.
That wouldn't tell you
whether it's a forgery or not
but we looked at a cross
section here and so the stamp,
this is the edge of the stamp.
It's been sliced through
and that's the edge
and on this side is
the Prussian Blue.
And this is the fabric of the
stamp and what we discovered
over here was small grains
of ultramarine blue
in the genuine ones.
And so the stamp maker
had put ultramarine blue
in as an optical brightener
because paper yellows with age
and so you keep, if you put
in in the first place
some complimentary color,
and ultramarine blue
is the ideal thing,
that's what actually
happens there.
The forged ones, as
far as we could see,
never had the ultramarine
blue in.
Now you can move across and look
and we have studied a large
number of icons of this sort.
This is Saint Athanasius
of Mount Athos
in a really bad state of repair.
Mount Athos is on the far
Eastern corner of Greece sort
of facing the Dardanelles.
It has 43 monasteries there
and hasn't been a female
there for 1,000 years.
I'm not sure what
you read into that
but there's not been
a cat either.
But I did go there one
Christmas and if you really want
to see Monk's driving
4X4's in black capes in hat
up snow roads, that's
quite an experience.
But the actual churches
left quite wide open
and so anything hanging in
these churches has quite a lot
of exposure to the elements
and they do degrade badly.
You can see this one
has had a terrible time.
It's been over painted
and even some of the
over paint has fallen off.
And you can shoot a laser beam
down in various places and see
and track and see
what the pigments are
at different depths.
You could also take
samples, cross sections
and this is a cross section
of the Saint Athanasius one.
And if you look then
this is the wood.
That's the original
painting, that layer.
Then there's a point
layer, kind of ground layer.
Then there's the varnish layer
and then there's
the over painting.
Now through all that mess
you can learn some things.
That red crystal there
gives this spectrum,
which is caput mortuum,
a form of iron oxide.
The blue gives this
spectrum which is azurite,
a copper based carbonate.
Then there's a lot of
white material there
which we've identified.
Then there's the
varnish and then
up here the three gives you this
spectrum which is carbon black
and then up here the four,
that's zinc sulfide in the form
of lithopone, which again
is a modern pigment.
You expect the modern ones
to be on the over painting.
So we can tell them
what's there.
Of course it's up to them to
decide what they want to do,
whether to restore the surface
painting or take it all down
and restore the original
painting.
I suspect that many of these
icons are in such bad order
that they can't do any
restoration at all.
You could also look
further at other things,
archeological treasures.
And it so happens that
the V&A Museum has a vast,
several hundred items from
Samara, which sort of collapsed
around 892 A.D. And all
wonder of Samara was buried
for 1,000 years or so until
certain experts went out,
German experts went
out and brought back
to Europe several thousand
items of broken ceramic work.
And the V&A museum got about 300
of these and they've been crated
up for almost a century.
We managed to get the first look
of these just two years ago.
And you see these fragments are,
because they've been
buried suffered no damage
after they fell apart, they're
actually in very good order
and it's no difficulty
in identifying what these
pigments are and they turn
out in general to be more
or less the same pigments
that are used in artwork.
And there's no end
of experimentation
that could be done there at
the V&A if they wish to do it
on the other 300 or
so things they have.
And they also passed
onto us a stucco fragment
from the Alombra, supposedly
plaster work of 14 century.
So we had a look at that
and especially at the blue
in these grooves here and that
is unambiguously passion blue,
first made in 1704 and so the
only thing we can tell them is
that either this is a
replica or it's been repainted
and so that part is certain.
We can't tell them
more than that.
It should have been lazurite,
would originally have been
lazurite to go through Grenada.
There's some other things
which were much more
obviously forgeries.
I had four Egyptians come and
see me once and it turned out,
again this is the sort of
dinner table conversation.
It was quite a long story
and very funny in parts.
But these four Egyptians at
the end of the day wanted
to sell 100 Papyrus at 2
million pounds each in London.
And this is one of them
and that's another one.
And I had a quick look
at that white worried me
and I had someone, Lucia Bergio
[phonetic] who's actually worked
at the V&A, she was very
keen to look at papyrus.
UCL wouldn't give us
any at that stage.
They had plenty.
So we had a look at this
one and it has gypsum
and calcite on it, no problem.
They are minerals.
You'd expect that.
It had anatase on it.
Anatase is a mineral also
but as a mineral it's
always deeply colored.
It's either black or deep blue
or can be brown,
all sorts of things.
I'd never seen native
Anatase white.
We are surrounded by it.
Normally there'd be, even
back here would be anatase
because it's #40 chemical in
the world, always in paint,
whatever the color because it
scatters light extremely well
and they sell it from how
white they can make it.
Well that white on Nefertiti's
dress was very white.
We looked at it and we know
from the pigment, grain size
and everything that that
is certainly synthetic.
They were unimpressed
with that information
but they were even less
impressed of the fact we found
about seven other pigments
which were also modern including
the [inaudible] blue, 1936.
It's not 1250 B.C. and that's
what the peachy museum ones
looked like.
I mean they're brown because
they're mainly iron oxides.
You'd think I'd never
look at another Papyrus
but I did have a friend
in the states call me a
few years ago and say look.
He'd been to Luxor and bought
from a very posh looking
shop quite a nice Papyrus
and he was thinking of leaving
it in his will to his son
and he was going to fly
it over from the states.
Well he did do that but we
didn't even need to get that one
under the Raman microscope,
although that certainly
confirmed it.
We got it under an ordinary
microscope and that had rows
of yellow dots, rows of red
dots and rows of blue dots.
It was clearly the product
of an inkjet printer.
[laughter] So I had to advise
him he probably didn't need
to mention it in his will.
So I'll just finish with
one other example here,
the so called the Spanish forger
who was extremely successful.
What was forged was
Jorge Ingles,
a 15th century Spanish
painter who was greatly admired
and what the chap, they
started getting suspicious
because there were too
many of them in circulation
and coming up for sale.
And if you look at them
you find that they're all
on medieval musical pages, at
least one side is musical notes,
staff lines and initials
and but definitely medieval,
medieval paper or velum
and what have you.
On the other side was scraped
clean and he'd do his forgery
on that side, by about
1950 they were realizing
from stylistic grounds
there were things wrong
and there were quite
a lot of these about.
The V&A museum bought five
of these only about a couple
of years ago and we were lucky
enough to have a look at them.
Now they're actually
very attractive.
The chap made a really
good job of them.
And you can see there are the
five and this is the Verso
with the medieval
inscription still on it.
They're there and there's
no problem with this.
But if you actually put
these apparent forgeries
under the microscope
what you find is this,
there are some undateable
pigments
but there are four
modern pigments.
There's chrome yellow 89,
shields green 70 and 75,
emerald green 1814,
ultramarine blue 1828.
These four are signatures of
something post 15th century
and so now a days if any more
of these crop up you just put it
under a Raman microscope and you
will find these four pigments
for sure.
So that's the first scientific
investigation of these.
I'll just finish to
show you what happens
when something goes
wrong in the atmosphere.
This is also at the V&A
museum, a pair of dividers here,
German watercolor 1585,
what's happened to that hand?
If you look more closely
at the hand you'll see
that it's all blackened and the
parts that would be brightest,
high lit as it were,
are the blackest.
And if you look at those in
the black, it's lead sulfide
and it's, what the artist did
would make those the whitest
part, basically a carbonate.
But there's been hydrogen
sulfide around either
from the atmosphere
or from bugs eating
up the sulfur containing binders
and generating hydrogen sulfide.
So that's a really bad
example of what can happen
in degradation circles and this
seems to be about the ultimate
that this particular one,
goodness knows how much hydrogen
sulfide got around there
to attack the white lead.
So I think that just gives an
idea of this particular way
in which science now
impinges on artwork.
[applause]
