Electron Emission Radiography of Panel Paintings

The Radiography of Panel Paintings by Electron Emission
Author(s): Charles F. Bridgman, Sheldon Keck and Harold F. Sherwood
Source: Studies in Conservation, Vol. 3, No. 4 (Oct., 1958), pp. 175-182
Published by: Taylor & Francis, Ltd. on behalf of the International Institute for
Conservation of Historic and Artistic Works
Stable URL: https://www.jstor.org/stable/1505008
Accessed: 02-05-2020 13:25 UTC
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Studies in Conservation
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CHARLES F. BRIDGMAN, SHELDON KECK and
HAROLD F. SHERWOOD
The Radiography of Panel Paintings by
Electron Emission
Received 19/5/58
materials are irradiated with very penetrating
X-rays, they emit electrons.' The intensity of
RADIOGRAPHIC examination of paintings is not
new; in fact, shortly after RSntgen discovered
X-rays in 1895, radiographs were being
made of paintings [I]. Improvements in X-ray
equipment and films and an understanding of
the technical problem involved have facilitated the examination of paintings on canvas
and the interpretation of radiographs. However, difficulty has been encountered in the
rr'
44;
radiography of panels fitted with wooden
cradles on the backs to prevent warping (Figs.
I and 2), as well as those on panels that might
be as thick as 1I inches with paintings on both
sides. X-rays are absorbed to varying degrees
by everything they traverse-the layers of
paint and ground, the wooden panel, and the
cradle. In the radiograph (Fig. 3) we see much
of the image of the portrait; however, superimposed on this is the structure of the wooden
panel with the twisting wormholes filled with
lead. There is also the image of the structure of
the cradle with alternate rectangular areas
denser than the others. These are caused by the
spaces between the battens of wood forming
the cradle. It can readily be seen how these
images of the panel and cradle interfere with
complete visualization of the image of the
paint layer.
Methods have been devised to eliminate
FIG. I. Reverse of panel showing cr
holes, and painted accession num
1The various methods of analysis
these unwanted images. One has employed an may be briefly described as follows:
arrangement whereby the film and painting
Conventional radiography-A photo
are moved during the X-ray exposure in
such a manner that the image of the cradle is
blurred more than that of the pigment [2].
We have approached the problem from a
different direction, based on the fact that when
produced by the differential absorp
they pass through a specimen.
Electron emission radiography-Und
tion, the various elements in a specim
intensities of electrons. These elec
graphically recorded to produce an
175
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176 C. F. Bridgman * S. Keck * H. F. Sherwood
-:: . ! :. :..- - -- - ---. --- .------ ---
? i?. . ? . .. ?ii~iii ~ .. . . . . .........: .... .
...... . :
..4.
?":.....
::..........
J i'":
.
...,.........
: ..... ,, :l!ii":i:;;i," i ?~
T:1i
...,."
-1.N , ':":"
--MM
, .... . .:....
24.. :.
t .....: .". ."
i'ni%
N i.
-M ? '.i: ? .,:
i......
N-V
.. . . "V
'3!
"n,,;,,N
FIG.
2.
'Portrait
Brooklyn
Photograph
X-ray
of
Museum
C
made
diffraction--The
this emission depends upon the material. It is
c
specimen
deflect
X-ray
negligible for light elements,
such as carbon,
angles.
The
pattern
of
but increases
as the atomic number of
the sub- s
characteristic
of
the
part
stance increases. Thus, pigments differing
in
X-ray
fluorescence
anal
composition, such
as lead carbonate, zinc
oxtion,
elements
emit
spec
escence
X-rays.
ide, chromiumAnalysis
oxide, or mercuric sulphide, o
some
of
the
elements
will differ
in their electron emission when in
tion.
irradiated. These electrons in turn will affect
The present paper is concerned only with the second
of these methods.
a photographic film in contact with the pig-
ments.
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Radiography of Panel Paintings by Electron Emission 177
.....
..
...
..
.
~~KA A
..
.......
..
.
.
.
..
i.1A
'Al
-X
Z-?
IF~
ee:.
ICw
e,-W
. . . . ......
. .... .
..
.
..
.
It
ACM
ED
r
A?
0
FIG.
3.
Radiograph
wormholes,
and
acc
its losses.
The use of this method has been helpful in
many fields, such as metallurgy and phi-
lately [31. Even the design on a postage stamp
will emit electrons if the printing ink contains
heavy metallic pigments.
The electron radiograph of the little portrait
is most enlightening (Fig. 4).1 Not only is the
1The electron radiograph is printed as a positive
image so that it will be easier to interpret alongside the
standard X-ray image, which is a negative.
image of the cradle entirely absent, including
the accession number painted on it, but also
the image of the panel with its filled wormholes. The brushwork of the ground, as well
as of the paint layer, appears to be recorded.
Note the horizontal brushstrokes which are
completely continuous from left to right, extending throughout the entire painting, background, hat, face, beard, and garment. These
seem to be caused by irregular horizontal
AA
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178 C. F. Bridgman * S. Keck * H. F. Sherwood
........ ..
.. .......... ...
..
.
..
.
.
..
......
....
FIG.
4.
Electron
are
not
recorde
densities
in
the
as
well
a
be
the
image
of
A
photo
lar
thicknesses
i
the
exte
the
paint
layer
for
com
both
large
and
(Fig.
4)
irregular
areas
blac
of
materials
of
low
indicatio
After
the
rad
due
to
t
the
painting
w
employ
routineorigina
proced
emission
dition
of
the
p
removal
excepti
of
the
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Radiography of Panel Paintings by Electron Emission I79
,iiiiN "
[!..: .i,
:: ::iiiii'i liiHii i : ?':'ii;
; ? . .... :: i
? .. :[ .:..... . *..? ? + ? ., .:? .i .
? ?;-. ? ? a:; ai: .0 . ... . . . . . . ::
....'~ll,:.,
i:,,_?;;;;" ........ 3 i .. .:i:% .,
" ..::.... ?.iil~: ? ?' ' ?:::?:-
i 1::".:
: .. "i;~l:ii'i
. [! ? ?.ii.. ?. ?...::"
:i~i~~ir
: .i!
?iiii
?:~:.ii
. ? ::..!
i l i~
:.-
iii:;i
FIG.
5.
P
may
be
These
amined for cleavages, loose ar
paint, or for exte
radiogra
sive worm tunnels which might cause collaps
the
of paint under
rest
vacuum. If it is free of these de
compose
fects, it is considered safe to proceed. With
sheet of X-ray film on the paint surface, it
TECHNIQUE
then placed in the open end of the bag in th
In as much as the bare film must be in
intidarkroom.
The open end of the bag is closed
mate contact with the surface of the painting,
rolled, and clamped. After this, the bag
a large, light-tight bag of black vinylcarefully
plastic
carried into the exposure room an
was devised with a fitting for the attachment
of
centered
with respect to the X-ray tube (Fig
6). The
a vacuum line [4]. The painting is first
ex- photographic effect of the primar
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I8o C. F. Bridgman * S. Keck * H. F. Sherwood
w.Ma?
..
.........
...
....
.
..
............
...
...
-z
EV
-Vgz
SE
Zr
i'W
11..I
FIG.
6
radiati
sev
mov
electro
by
the
wh
with
t
elec
X-rays
exp
face,
b
40tion at the tube. Kodak
No-Screen Medical
the
act
to
X-rayenh
Film was used.
vacuum
is
prod
SUMMARY
ment
l
cessive
The utilization of electron emission r
unnece
than X-radiation makes it possible to
Electro
satisfactory images of the paint layers o
penetr
ings. Images obtained from electron
betwee
cannot supplant those formed by X-r
1 The authors do not know of any instances
whereby
However,
the technique is particularl
paintings have been damaged by X-radiation,
although on panels which are thick
for paintings
such might be a possibility. Chemical changes may be
heavy reinforcement.
produced by penetrating radiation, but such a reaction
The
image created by X-radiation
generally requires a dose many orders of
magnitude
will
reveal information
greater than that used for elecz:on emission
radiography.
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concerning n
Radiography of Panel Paintings by Electron Emission 181
:; ..:? .[:. i:
...
? :: ":::..I:.i
N.,
.i :..:
.. : .. .ii ? :. ?
lid
....
N 4- . . .. .::.
.:'N-.' N
, . :: : z:... 4:R.......... . ...: . .
. .. . . M : .::.
i~~~Iii ;.:!ii
? .. .. ..:::.: :
NE.: :
:.j
:.,::::....
..mm
..........~ ~ :ti~i iil i igiixi:
-i:
? .. !tilill
N ....:...
4 ::.A Tu 5 ::::
s., x-. . . ?. .
"p. %"::,
N4.. - .: n!
iti
i:
i i:;i:l;!i iN;/iii
:l
N::
::? :: ii~~.
:s:grg':'
... ::l~a~iij N.
N No .'si
?:?i~*::?i
si"iiEi~i B
4 N ':x'i
s:
N~-:1.
::::x
.. . .. . .. .
Fi,
Ux.?
-:: 4 ..... ... ? i:. ....
Ei "!III.
N..
-XI
?;Fif,
N?
. . ... .. ...
is; :
FIG. 7. On the left side of this electron radiograph a sheet of paper has been
interposed between picture and film. This absorbs all electrons, leaving only
the very faint primary X-ray image that is also produced. (Negative image.)
the pigment layer or layers but alsoHowever,
the sup- this is merely conjecture an
specific
rule can be established.
port, whether it be canvas or wood. The
image
obtained from electron emission (Fig. 4), on
CHARLES F. BRIDGMAN
the other hand, reveals information concerning
SHELDON KECK
only the paint layer. If the paint layer is very
thin and low in density, electronsEastman
from
an
Kodak
underlying pigment layer might conceivably
Rochester 4,
penetrate it and record an image on N.Y.,
the U.S.A.
film.
HAROLD F. SHERWOOD
Co.,
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182 C. F. Bridgman * S. Keck * H. F. Sherwood
References
I Editorial. Electrical Rev., London, 30 April, 1897.
2 PEASE, M., 'A Note on the Radiography of Paintings', The Metropolitan Museum
of Art Bulletin, Iv, pp. 136-9, No. 5.
3 POLLACK, H. C., BRIDGMAN, C. F., and SPLETTSTOSSER, H. R., 'The X-ray Investigation of Postage Stamps', Medical Radiography and Photography, xxxI,
pp. 74-8.
4 SHERWOOD, H. F., 'Vacuum Exposure Holder for Microradiography', Review of
Scientific Instruments, CCCxvnI (1947), pp. 80-3.
LA RADIOGRAPHIE DE PEINTURES SUR PANNEAU PAR EMISSION
ELECTRONIQUE
Resume
L'emploi d'dmissions 6lectroniques plut6t quel'image produite par emission 6lectronique
de rayons X rend possible l'obtention d'images(Fig. 3) ne fournit que des renseignements
satisfaisantes de la couche picturale des tab- sur la seule couche picturale. Si celle-ci est
leaux. Ces images ne remplacent pas cellestris mince et a faible densit6, des 6lectrons
obtenues " partir des rayons X, mais cetteissus d'une couche pigment&e sous-jacente
pourraient le cas 6cheant pin6trer dans la
technique est particuli&rement utile pour des
panneaux 6pais ou fortement consolides.
couche picturale et former une image sur le
L'image fournie par les rayons X (Fig. 2)film. Ceci, cependant, n'est qu'une simple condonne des renseignements non seulement surjoncture, et on ne peut 6tablir de regle fixe.
la (les) couche(s) pigmentie(s) mais aussi sur
le support en toile ou en bois. Par contre,
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C. F. B.
S. K.
H. F. S.