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Some Factual Observations about Varnishes and GlazesAuthor(s): Neil Maclaren and Anthony WernerSource: The Burlington Magazine, Vol. 92, No. 568 (Jul., 1950), pp. 189-192Published by: The Burlington Magazine Publications Ltd.Stable URL: http://www.jstor.org/stable/870432.
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NEIL MACLAREN and ANTHONY WERNER
o m e
actual
bservations
a b o u t
arnishes
n d
Glazes
SINCE
1946
there has been considerable
controversy
about
the methods used
in
the
cleaning
of
paintings.
It
was
occa-
sioned,
in
the
first
place,
by
the
results of
the
cleaning
of
pictures
at
the National
Gallery
in
the
immediately
preceding
years.
The National
Gallery's
practice
was
expounded
in
the
catalogue
of
the Cleaned Pictures Exhibition
of
I947,which
presented
all
the relevant evidence
in
greater
detail than had
previously
been
attempted
by any
other
gallery.
The
pictures
cleaned
at
the National
Gallery
and the
methods used were
also the
subject
of an
investigation
by
an
independent
inter-
national
commission,
the
Weaver
Committee;
the
report
of
this
Commission
approved
the
work
done
at
the
National
Gallery.'
Although
the
controversy
had some beneficial
effect
in
stimulating
intensive
reinvestigation
of
the
basic
problems,
it
had,
at
the
same
time,
the unfortunate result of
leading
some
people
to
believe that
there
were two
sharply-
defined schools of
thought,
the
'partial
cleaners' and the
'radical
cleaners',
and resulted
in a
most unrealistic
simpli-
fication of the whole
position.
Subjective
considerations
tended to obscure
facts,
upon
which alone fruitful discussion
can
be based. Considerable interest
was, therefore,
aroused
by
the
publication
in
this
journal
of an
article
defending
the
thesis of
'partial' cleaning,
entitled
'The
Cleaning
of
Pictures
in
Relation
to
Patina, Varnish,
and
Glazes',2
since
its
author,
Pro-
fessor
Brandi,
claimed to have found
during
the
treatment
of three Italian paintings factual evidence in support of some
of his contentions.
The observations which follow are
offered
because the
present
writers
believe that the article
in
question
contained on the
one
hand
insufficient evidence to
justify
the
assumptions
made
and,
on the
other,
a
number of demon-
strable errors of
fact.
There can be no
end to discussion
of
the
purely
aesthetic
aspects
of the
subject,
and it is
proposed
here
to
confine discussion to the technical
side
of
the
question,
especially
since this
aspect provides
the
substance
of
Professor
Brandi's
essay.
Let
it
suffice to
say
that it is
presumed
to
be
beyond
dispute
that
the aim
of
those
entrusted with
the
care
of
paintings
is to
present
them as
nearly
as
possible
in
the
state
in
which the
artist
intended
them
to
be seen.
Throughout
the
recent
controversy
the
issues
have been
confused by the indiscriminate use of certain terms, in par-
ticular
patina,
varnish,
and
glaze.
For
example,
the author
of
the article under
consideration states that 'it
can be
proved
that what we call
patina
can more
often than not
be
shown
to
consist either of
glazes
or of
tinted varnishes'
and that
'the
upholders
of total
cleaning'
claim
that
'dirt,
varnishes accu-
mulated
over centuries . . . are
being
palmed
off as
patina'.
In
fact,
an
attempt
is made to treat the terms
patina,
varnish,
and
glaze
as
synonyms.
If
there is to be
any
clear
thinking
about
the
problems
involved
in
picture cleaning
it is
impera-
tive that the essential terms be used
consistently
and bear
their own distinct
meanings.
For this
reason,
it is
proposed
to
state
as
precisely
as
possible
what
the
present
writers con-
ceive to be the normal
meanings
of the terms
patina,
varnish
and
glaze
as
established
by
usage.
Patina.
This
term was
originally
applied
exclusively
to
bronzes,
and referred
to the natural
chemical
changes
which
occur
in
the surface
layer
of
bronze.
From
the Renaissance
onwards the term was extended to include artificial surfaces
applied
to bronzes to
simulate
these
changes.
The reference
by Vasari to this well-known practice, quoted by Professor
Brandi,
has
nothing
to do with
pictures.
Later the
term was
by analogy applied
to
paintings though,
to
judge by
dic-
tionaries
of
the fine
arts and
other
similar
writings,
this
usage
was not common outside
Italy
before the nineteenth
century.
Indeed,
as Baldinucci's definition
clearly
shows,
this
exten-
sion of
the
meaning
was
applied only
to
the
natural
changes
induced
by
time;3
there
is no
evidence
that
these
changes
were ever
artificially
simulated on
paintings
by
their
authors
until
comparatively
recent times.
If
patina
is to have
any
meaning
in
connection with
painting,
it must
be confined
to
those
changes
in
colour and
surface which take
place
within
the
paint itself,
as the result of chemical
and
physical
processes
n
the
course of
years,
such as
darkening
of
medium,
fading
of
pigments,
craquelure.
It
is these
changes
that
give
an 'Old Master' its physical character. Such subsequent
accretions to the
painted
surface as later varnishes and dirt
cannot
be considered
as
patina.
Nor
can
patina
ever 'consist
either of
glazes
or of tinted
varnishes';
if
applied
by
the
original
artist these are
an
integral
part
of
the
painting,
not
a fortuitous effect
produced
by age.
It
is, therefore,
absurd
to
speak
of the 'function' of
patina,
since
it
is an
effect
due
to
time alone
and
outside
the control of
the artist.
In
relation
to
paintings
the term
is at
best
redundant,
since the several
conditions
it
covers
can
be
more
precisely
described;
if
loosely
used,
a source
of
confusion. It
would
seem
advisable
to avoid
it
altogether
in
connection with
pictures.
Varnish,
n
modern
usage,
denotes a
solution
of a
resin
in
an
organic
solvent.
Depending
upon
the nature of the solvent
used,
varnishes
may
be divided into two main
types:
(a)
oil
varnishes,
prepared by dissolving
a hard or soft resin in a
fixed4
oil,
such as
linseed, walnut,
or
poppy
oil;
(b)
spirit (or
essential
oil5)
varnishes,
made
by
dissolving
a
soft resin
in a
volatile solvent
such as alcohol or
turpentine.
It is
indispen-
sable
to
distinguish
between these two
types,
which
differ
fundamentally
in their mode of
drying
and in the nature of
1
The essential
part
of the
Weaver
Report
will
be
published
in
Museum,
Vol.
Im
[1950],
No.
2.
2
THE
BURLINGTON
MAGAZINE,
Vol.
xcI
[1949], pp. 183-188.
8
F.
BALDINUCCI:
Vocabolario oscanodell'Arte del
Disegno [x68i], p.
x
x9:
Voce
usata
da'Pittori,
diconla ltrimenti
elle,
ed ?
quella
universalecurit&hhe l
tempofa
apparire opra
e
pitture,
che anche alvolta
efavorisce
(the underlining
is
ours).
*
i.e.,
oils which do not
evaporate
at
room
temperature
and cannot be
distilled
at
atmospheric pressure
without
decomposition.
5
i.e.,
oils
which
are
volatile and can be
distilled without
decomposition.
189
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8/11/2019 870432 info about MS
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SOME FACTUAL OBSERVATIONS ABOUT
VARNISHES
AND
GLAZES
the
film
formed. The
first
dries without
evaporation
of the
solvent,
forming
a
tough
film
which resists the solvent action
of
the neutral
organic liquids
normally
used
in
cleaning
(e.g.,
alcohol, acetone,
xylene, etc.), although
it can be dis-
integrated by
certain alkaline
reagents
such as
ammonia,
soda,
or
morpholine.6
The second dries
by evaporation
of the
solvent,
forming
a film
whose
solubility
is much
greater
since
it
depends wholly
upon
the
nature
of the
resin used.
Confu-
sion of
thought
sometimes
arises from
the
changes
in
meaning
which the word has
undergone:
the current
meaning
is often
inadvertently
transferred
to the earlier texts.
Originally,
the
term
varnish
(Latin
vernix,
talian
vernice,
tc.)
was
used
only
for
a
dry
resin;
the term
'liquid
varnish'
(verniceiquida)
was
applied
to
a
solution
of resin. After the sixteenth
century
the
word
came
more
and more
to
have
its
general
modern
meaning,
i.e.,
a
transparent
surface
coating.
But,
from
the
introduction of oil
painting,
varnish was
not
used
solely
as
a surface
coating;
it was also often added
to media to
im-
prove
their
handling
and
finish,
or to hasten
drying.
Modern
readers sometimes
erroneously
assume that the
'varnish'
added
to
paint
for these
purposes
was of the same
kind
as
that
employed
in
modern surface varnishes.
This
point
is
discussed
further
below.
A glaze is a translucent layer of little pigment
and much
medium,
applied
over
a
(usually)
lighter
stratum
which shows
through
it.
It
would be
difficult
to
improve
upon
de Piles'
description:
Une
couleur
glacde
n'est
autre chose
qu'une
couleur
transparente
u travers e
laquelle
n
peut
voir
e
ond
sur
lequel
lle
est
couchle.
On
glace
sur les bruns
our
leur
donner
lus
de
orce,
et
sur les couleurs laires et blanches
our
les
rendre
res
vives
et
dclatantes.7
t is
clear
that the main
purpose
of
glazing
was
not,
as is often
assumed,
to
veil
or tone down
colour,
but
to
intensify
it.8
Expressed
in
purely
optical
terms,
the
glaze
layer
reduces
the amount of white
light
diffused
from
a matt
surface,
thus
conferring greater
depth
and
brilliance
of
colour
on the
underlying paint.9
A
typical
example
is the
glazing
of
vermilion with madder
lake
to make the former
even
more
fiery.
It is
presumed
to be
common
ground
that
the
aim of
pic-
ture
cleaning
must
be
the
removal,
without
damage
to
any
original
work,
of
all accretions
which
distort the artist's
intention.
Pictures
have been cleaned
and restored
from
the
earliest
times
and,
judging by
the records
preserved
in
some
cases,
it is obvious that
most old
pictures
must
have
been
frequently
cleaned
throughout
their life. The
heavy-handed
methods and
powerful
reagents
often used
until
compara-
tively recently
sometimes
resulted
in
serious
damage,
and not
many
old
paintings
have
survived
in
virgin
condition.
The
removal
of darkened varnish
and
repaint
naturally
reveals
this
damage,
and
it
may
be
unjustly
attributed
to
the modern
restorer and
his methods.
Cleaning
can,
in
fact,
be
performed
safely as long as later accretions on a painting are more
soluble
than
all
parts
of the
original
paint.
It is not
generally
contested
that
body
colour
can,
except
in rare
cases,
be
cleaned
with
safety.
As Professor
Brandi's
article
shows,
the
main
objections
to
complete
cleaning
are
based
on the fear
that
part
of the
artist's intention
in
the
form of
patina,
glaze,
or
varnish
may
be removed
or
damaged
in the
cleaning
process.
This
fear,
however,
arises
from
an
incomplete
under-
standing
of the
solubility
of
surface varnishes
and
glazes.
(It
may
be
remarked
in
passing
that since
true
patina
is an
organic part
of
a
painting
there can
be no
question
of its
removal
by solvent.)
Despite
Professor Brandi's
assertion,
it
is
difficult
to
believe
that
any
modern
restorer
or art-historian
has
'ignored
the
existence
of
glazing'.
It is
incorrect,
moreover,
to refer to
glazing
as
a
'secret
remedy
. . .
unlikely
to
be
readily
ack-
nowledged'
which
'maintained
an almost
illegitimate
and
underground
existence
in
painting'.
The
employment
of
glazing
from
the earliest
times is
surely
universally
recog-
nised.
Far from
being
the
case
that
'the method is hinted at
for the first time
by
Armenino', i.e.,
in
1587,
the
essentials of
the
technique
are
in fact described
by
Pliny,
in
the
Lucca
MS.
of
the
eighth
century,
and
in
many
other
manuscripts
prior
to the
sixteenth
century.
Many
authorities even
suppose
that the full
technique
of oil
painting
developed
from
the
use
of oil
glazes
over
tempera
(the
so-called
'mixed
technique').
The
recipes
for
glazes given
in
the
historical texts
(see
below)
lend no support to the wide-spread belief that because glazes
produce
a delicate
visual
effect
they
are
ipso acto
chemically
delicate
and
therefore
very
sensitive
to the solvents
normally
used
in
cleaning.
It
will be observed
that,
in Professor
Brandi's
article,
neither
historical
nor
experimental
evidence
is
produced
in
support
of
this
belief,
although
there
must
have
been
ample opportunity
for
obtaining
experimental
evidence
during
the
treatment
of the
three
paintings
there
mentioned.
Indeed,
although
it is
the crux of the
matter,
the
whole
subject
of the
solubility
of
glazes
is
passed
over
in
silence.
Although
it is difficult
to make
a chemical
analysis
of
media used
in
glazes
-
or,
indeed,
of old varnishes'0-
chiefly
owing
to
the smallness
of
the
samples
available
in
practice,
the bulk of the evidence in the historical texts
goes
to show
6
With
regard
to the effect
of
solvents
on
linoxyn (i.e.,
dried
oil),
it must
be
stressed
that
there is
no
question
of
a
straightforward
solvent
action. Neutral
organic liquids
swell the
linoxyn,
transforming
it
into
a
spongy
mass
(technically
termed
a
gel)
which is
removable
by
friction. These
liquids
vary
greatly
in the
extent
to which
they
can
cause
this
swelling
to occur.
Alkaline
solvents,
such
as
ammonia, soda,
or
morpholine,
are more
drastic
in their
action;
they
de-
compose
the
linoxyn
and
dissolve
the
products
of that
decomposition.
7
R. DE
PILES:
Elementsde
la
Peinture
pratique
[ed.
1776],
p.
II7.
Cf.
also
WATELET
and
L.VESQUE:
Dictionnairees
Arts de
Peinture,
tc.
[I792],
ii,
article on Glacis;
j.
F.
L.
MERIMAE:
De la peinture
a
'huile
[I1830],
pp. 95-8;
A.
EIBNER: Malmaterialkunde
Igo9],
pp. 53-6.
The definition of
glazing
given
by
MILIZIA
[1827]
and
quoted
by
Professor
Brandi seems
to be
a
garbled
abridgement
of
the article
in
Watelet's
dictionary
(see
above).
The reference to
glazing
in
de Piles
alone is
sufficient
to
disprove
that
glazing
was
a
'clandestine'
practice.
s
Confusion
seems to have arisen from the words used
for
glaze
in
Italian:
velare,velatura,
which
by
reason of the other associations of the word velare
have
led some
to
think
of
a
glaze
as
a
'veil'. The words used
for
glaze
in French
(glacis)
and
English
convey
much more
clearly
the idea of
the
optical
effect
produced.
The
effect of
'veiling'
is
more
nearly given by
means of
a scumble
(French:
frottis)
-
a
semi-opaque layer
normally applied
over
a darker
stratum.
'
A detailed account of the
optical
principles
involved
in
glazing
is
given by,
among
others,
A. ZILOTY: La dicouverte de
Jan
van
Eyck [ed. 19471,
pp.
24
ff.
and
38
ff.
0o
Professor
Brandi
states
(op.
cit.,
p.
'187,
note
13)
that
the head of
the
laboratory
of
the Istituto
Centrale
del
Restauro,
Dr
Liberti,
demonstrated
by
means
of
analyses
the
presence
of
specific
resins
in old varnishes
removed
from
paintings.
Dr Liberti
has
kindly supplied
us
with a detailed
account
of
the
analytical
methods used
by
him. The
tests
employed
(the
Storch-Morawski
reaction,
determination
of
softening
and
melting
points,
solubility
and
refrac-
tive
index)
can
rarely
lead
to the
positive
identification
of
an individual
resin,
even
when
it is
a
question
of
a fresh resin
specimen.
The tests
are
quite
unreliable
when
the resin
is
a
component
of
an old
varnish;
in
such
a case
the
physical
properties
of
the
resin will
have altered
considerably
with
time.
Furthermore,
the
presence
of
oil
in the varnish
is
another
factor
which
makes the
identifica-
tion
of
a resin
extremely
difficult.
This factor
has not been
taken
into
account
by
Dr
Liberti.
9go
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SOME
FACTUAL OBSERVATIONS
ABOUT
VARNISHES
AND
GLAZES
that the medium used
for
glazing
before the
eighteenth
century
was
either
oil
alone or oil mixed
with a
small
quantity
of
varnish.
Glazes so
composed
would
have,
in
fact,
a
high
degree
of
resistance to the solvents
now
normally
used
in
cleaning.
Where
the medium was
oil
alone
it would form
a
linoxyn
(i.e.,
dried
oil)
film,
similar to that
of the main
paint
layer
and,
consequently,
not more
soluble. Where
the
medium contained
varnish,
the bulk of
the evidence
goes
to
show that the varnishin questionwas of the oil and not of the
spirit type,
i.e.,
highly
resistant to solvents.
The
varnishes
used for this
purpose
in
Italy,
for
example,
were known
as
vernice
iquida
gentile,'2
vernice
iquida,'3
and vernice
commune.14
Confirmatory
evidence
of the resistance
of such
glazes
to
solvents
is
provided,
on the one
hand,
by
the
large
number
of
them
which have survived intact on
pictures
cleaned
by
the
more
drastic
methods of the
past
and,
on
the
other,
by
experiments
in the
National
Gallery
chemical
laboratory
upon
artificially aged
varnishes,
prepared
according
to
the
old
recipes.,
We have
noted above that varnish
was
also
sometimes
added
to
paint
media
to
improve
their
handling
and
finish;
this
is
mentioned,
for
example,
in the
fifteenth-century
Strasbourg
MS.16 and
by
Armenino.'7
The varnishes used
for this
purpose
were of
the
oil
type (as may
be seen
by
reference
to
Armenino's
text)
and
were,
in
any
case,
added
in small
amounts,
so
that
they
would not have
increased
appreciably
the
solubility
of
the
paint
film
when
dry.
It
should be
noted,
on
the other
hand,
that
Borghini
expressly
prohibits
any
additions to
oil media
when
painting
on
panel.'8
The addition of varnish
to
media was
usually
con-
fined
either to colours which had
little
substance'9
or,
when
used
throughout
the
paint
layers,
to
pictures
in
an
exposed
or humid environment.20
The
practice
was more
general
among
the
painters
of Northern
Europe.
Varnish
was used from
early
times
as a
general
surface
coating,
but this was
not an invariable
practice
and
pictures
were often left unvarnished
by
their
authors,
particularly
when
finished with
colours
mixed with varnish.21Before
the
middle
of the sixteenth
century,
surface varnishes
were
almost
exclusively
of the oil
type
and
would,
of
course,
be
very resistantto modern solvents. Very few original oil var-
nishes
can have survived
the inevitable
cleanings
of
the
past,
often with alkaline
reagents.
In the rare cases
where
they
have been
preserved,
their removal
without
damage
to
underlying paint
and
glazes
is made
feasible,
although
not
without
risk,
by
the
fact that surface varnishes
were
applied
at
a later date - Cennini
recommends
a
delay
of
at
least
a
year22-
so
that
they
did not become
an
integral
part
of
the
picture
proper.
The oil varnishes
had several
disadvantages: they
dried
slowly,
were rather
viscous
(and
therefore
inconvenient
to
apply),
and
they yellowed
badly.
These
defects
were,
no
doubt,
responsible
for the
gradual
introduction
of
spirit
varnishes,
which,
judging
from the historical
sources, began
in the first half
of the sixteenth
century,23
although
they
do
not
seem to have been
in
general
use
before the
beginning
of
the
following
century
or even later.
With time these
varnishes
also
yellow,
but not
so much as
those
of
the oil
type;
on
the
other
hand,
they
rapidly
become brittle
and
finally
disinte-
grate. They
can be
easily
removed
since
they
are
much more
soluble
than the dried
oil film. There is
no
evidence
that
these
easily
soluble
spirit
varnishes
were
ever
tinted
(i.e.,
pig-
mented)
by
the
original
artist
until
much
later
times,
no
doubt because
they
were not
sufficiently
durable. Nor is
there
evidence
that tinted
oil
varnishes
were used
as
general
surface
coatings.24They
were
sometimes
used
for local
application
in the manner
of a
glaze,
but
they
would,
in
this
case,
be
identical in every respect with an oil glaze and equally
resistant
to solvents.
It has been
contended
that
varnish
of
a
yellowish
tinge
was
applied
by
the
original
artist in order
to
provide
a
'general
unification
of tone'.
Professor
Brandi
suggests,
in-
deed,
that
early
varnishes had
a
yellow
hue
since
they
'nearly
always
contained
stone-oil,
that is
to
say
naphtha'.
The truth
of
the
matter
is
that
out of
forty-seven
recipes
for
oil varnishes
given
in the
principal
historical
texts,
only
four
11
Some
body
paint (e.g.,
vermilion)
is,
indeed,
less
resistant
to
solvents
than
an oil
glaze.
Is
This
varnish was
made
by dissolving
amber
(i part)
in linseed
oil
(3 parts).
(Cf. C. L. EASTLAKE:Materialsor a History of Oil-Painting [1847],
p.
242,
n.,
quoting
T.
ROSSELLO:
Della Summa
de'
Secreti
universali,
tc.,
Venice
[1575],
ii,
p. 127.)
18
EASTLAKE
(op.
cit.,
p.
229-241)
discusses
the
nature
of
this
varnish
and
gives recipes
from various
historical
sources. The
most
usual
recipe
requires
one
part
of
sandarac to be
dissolved
in
three
parts
of linseed
oil. The
addition
of
mastic
was
rare. This varnish
was
sold
ready-made
in
Cennini's time.
14
This
term was
usually
applied
to
a
varnish made
by
dissolving
resin
(pece
greca)
in linseed
oil.
Typical
recipes
are
given
by
L.
FIORAVANTI:
(Secreti
Rationali,
Venice
[1564],
Book
v,
chap.
67),
the Marciana
MS.
(chap.
405),
and
G.
B.
BIRELLI:
(Opere [16oi],
Book
xmI,
Chap.
372).
16
t
has
been
suggested
that the
sometimes
inexact
terminology
of the
historical sources makes
it difficult
now to
identify
the
ingredients
of
the
recipes
and, therefore,
impossible
to make
up
the latter in
the
laboratory.
Although
uncertainty
may
exist
in
the
case of
certain
recipes
considered
in-
dividually (though
the
great
majority
are
quite
precise), experiments
conducted
in the
National
Gallery
chemical
laboratory
involving
all
possible
alternatives
where
doubt exists
have shown
that
the
substances
mentioned can
almost
invariably be accurately identified and the recipes compounded. Indeed, in the
case of
varnish
recipes
the real
difficulty
is
sometimes to
determine the
purpose
for
which the
varnish was
intended,
as
may
be seen
from
the
remarks
(note 24
below)
on the
supposed
recipe
for
tinted
varnish cited
by
Professor
Brandi.
16
Chap.
71:
hie
merkedis varwen
ol
man
alle
gar
wol riben
mit dem
oli
. . . so
sol
man
under
eglich
varwedrie
troph
virnis
riben.
17
Dei
veri
Precetti
della
Pittura
[1587],
Pisa
(1823
ed.,
p.
138):
che
cosi si
ac-
compagnano
ulla
pietra
con
giungervi
dell'olio,
ed un
poco
di
vernice
dentro
commune,
perchequesta
vernice
di tale
qualita,
che
daforza,
ed
aiuto
a
tutti i
colori,
che
patiscono
nell'asciugarsi;
p.
141)
si
giunge
poi
con
verderame
n
poco
di vernice
ommune
di
giallo
santo;
(p.
143,
referring
to a
varnish
of
mastic
in nut
oil)
e
di
questo
e ne
puo
mettere
egli
azzurri
ini,
nelle
ache
e in
altri
tali
colori,
accio i
asciughino
iu presto.
It
will be
remembered
that
the vernice
ommune
hich
Armenino mentions in the
passages
quoted
was an oil varnish
(see
note
14).
18
R.
BORGHINI:
IlRiposo
[1584],
ii,
p.
176.
19
Cf.
ARMENINO:
10C.Cit.
20
Cf.
BORGHINI:
Op.
cit.,
p.
174.
21
Cf.
BORGHINI:
op.
cit.,
p.
174.
22
CENNINI:
Trattatodella
Pittura,
chap.
155.
23
The earliest
references
to
spirit
varnishes are
apparently
those in
the
Marciana
MS.
(sixteenth
century),
ALESSIO:
(Secreti,
Venice
[1555])
and
FIORAVANTI:
(Secreti ationali,
etc.,
Venice
[15641).
24
The recipe quoted by Professor Brandi (p.
I88,
note
I6)
provides
no evi-
dence
that coloured or tinted
varnisheswere in
use
as
general
surface
coatings
in
Italy
in the
fifteenth
century.
He was
presumably
led
to the
view that
this
recipe
was for a tinted varnish
because
of the
mention
of
red
lead
(minium)
and/or
vermilion
(cinabrum)
s
ingredients.
This varnish
was
prepared
in
the
National
Gallery
laboratory
according
to all
the
possible
variations of the
recipe,
and
in all
cases
resulted in a
dark
brown
substance.
It is clear
that
the
red lead
here
functions
solely
as
a
drier;
it
could
not act as a
red
colouring
gent
since on
heating
as
prescribed
the
varnish becomes
chocolate
brown. It
is
to be
assumed
that vermilion is
mentioned in
this
recipe
in the
mistaken belief
that it
is
synonymous
with
minium.
Some
support
for this
assumption
is
provided
by
the
alternative
reading
of this text
given
by
MERRIFIELD:
The
Ancient
Practice
f
Painting [18491,
p.
489:
minio
o
cinabrio. t is
extremely
doubtful
whether this
recipe
was
for a
surface
coating
for
pictures.
The
inclusion of
red
lead and
the
very
small
amount of
resin
suggest
that it
was
intended for a
drying
oil for
use
as a vehicle.
191
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5/5
SOME FACTUAL
OBSERVATIONS ABOUT VARNISHES AND
GLAZES
mention
naphtha (olio
di
sasso)
among
their
ingredients;
out
of
twenty-eight
recipes
for
spirit
varnishes,
only
seven include
naphtha.25
In
any
case,
even unrefined
naphtha
would
not
have
added
noticeably
to the
yellowish
tinge
which oil
varnishes
undoubtedly
possessed.
The
historical
texts,
how-
ever,
show that
the
intention
was to obtain
as colourless a
varnish as
possible
for
surface-coatings,
and that
it was
applied
as
thinly
as
possible.26
As
previously
remarked,
many paintings seem to have been left unvarnished. The
extent to which
the artist
may
have
allowed,
if
at
all,
for
the
colour of the fresh varnish must
remain a
matter
of
specula-
tion;
it is obvious that
he
could not foresee
the
degree
of
distortion that must result from
the
progressive
discoloura-
tion
which
age imparts.
Lastly,
in
support
of
his
general
thesis Professor
Brandi
has
produced
three 'witnesses'
in
the
form
of three
Italian
paintings
treated
at
the Istituto
Centrale
del Restauro.
It
is
reasonable
to doubt
whether
any
general
conclusions
can be
safely
drawn from evidence
derived
from
only
three
cases,
even
if that evidence
were
in
every
way
clear
and
beyond
dispute.
Nevertheless,
it
is
proposed
to
submit
the three
'witnesses'
to
a detailed examination
in
order to
determine
how
far
they
do
in fact
support
his contentions.
(i)
During
the
treatment
of
the Pesaro
Bellini
a
layer
of dark
varnish
was observed
in
an area
of S.
Peter's
halo
where
the
gold
was
missing.
It
was, therefore,
assumed
that this
varnish must
have been
put
on
by
Bellini himself
and
the
original
gilding
applied
on
top
of it. This conclusion
is
based
on the belief
that the
varnish 'would
necessarily
have
disappeared
with
the
gold'
if it
were
of later date. In other words it
is
apparently
contended
that
the
age
of a varnish is the
determining
factor
in
its
solubility.
This
ignores
the
fact that
an
oil
varnish '
only
a
hundred
years
old is
as
resistant
to solvents as
one
four hundred
years
old. A
more
obvious
and
simple
explanation
of the
dark
varnish
in
the
lacuna
would be
the
presence
of
damage
in the
halo
before
he
applica-
tion
of a
varnish
by
a
later
hand,
the
gold
itself
(at
least
in the
damaged area) being a restorationapplied over this later varnish.
Again,
in the
case of the
St Terence
redella
panel
it is
suggested
that,
because
it
was
found
impossible
at the
Istituto Centrale
to
remove the
yellowish
varnish
without
carrying
away
with
it
the
subdivisions
of
the stones and
their
clamps,
the latter were
glazed
in
by
Bellini
on
top
of a varnish.
This
area
of the
picture
has
suffered
a
great
deal
of
damage
and
not
only
have the subdivisions
and
clamps
been cleaned
away,
but
also
the
surrounding body
paint,
leaving
the
ground
bare
in
places.
It
seems,
therefore,
that
the
parts
of the
supposed
'glazing'
removed
at the Istituto
Cen-
trale were
old
restorations
covering
earlier
damage.
This
is
confirmed
by
reference
to
a
photograph
taken before
the
recent
treatment
in which some
of the
damage
and
retouchings
on
the
subdivisions
and
clamps
are
clearly
visible.28
(2)
When
an
eighteenth-century
frame
was removed
from the
Coppo di Marcovaldo Virginand Child,a layer of varnish was
found beneath
which
also
covered the
rest of the
picture.
This
was
claimed
to be the
original
varnish on the
improbable
assump-
tion
that no restoration
of
the
picture
had taken
place
between
the
fourteenth
century
(when
the faces of
the
Virgin
and
Child
were
overpainted)
and the
eighteenth century.
Even
if
one
ac-
cepted
the
supposition
that there
had been
no restoration
of the
picture
during
three
centuries,
there
would
still
be
no
proof
that
this
is an
original
varnish;
on the
contrary,
this
varnish cannot
ave
been
put
on
by Coppo
di
Marcovaldo
since
it also covers the
fourteenth-century
Ducciesque overpainting
of the heads. This
fact
clearly
emerged
during
two
lengthy
examinations
of the
picture
made
at Siena
in
1949
by
W.
P.
Gibson,
Keeper
of
the
National
Gallery,
and
one of the
present
writers.
Furthermore,
the
assertion
that
the
eagles
in
tondos
on
the
Virgin's
outer
veil
are
painted
on
top
of a
'transparent,
coloured
varnish'
(actually
brown)
is
disproved
by
the
fact,
observed
during
the course
of the
same
examinations,
that
although
the
'coloured'
varnish
has
been
removed
at some time
in at
least
one
place,
the
eagle
tondo
in this
area
(towards
the lower
edge
of
the
veil,
on the
left)
remains
intact.
The
true colour
of
the veil is
also revealed
at this
point.
Freed
from
varnish,
it is
a
very pale
yellow
and thus
disposes
of
the
further
argument
that,
since
the
under-veil
added
by
the
Ducciesque
author
of the
repainted
heads
was
white,
the
brown
varnish now covering Coppo's
outer
veil
represented
the
original
colour
with
which
the
white under-veil
was
to
contrast.
The
pale
yellow
now uncovered
would
have
provided
the
necessary
con-
trast.
Lastly,
the
ruby
red
paint
in
the
middle
of the footstool
(the
rest of
which
is
covered with
the deteriorated
remains of
original
orange
paint)
is
quite
clearly
later
repaint
along
the line of
a
crack
in
the
panel.
(3)
It
is claimed
that when
some
drops
of
old
candle-wax were
removed
from
Benozzo
Gozzoli's
Virgin
and
Childwith
Saints,
cor-
responding
areas
of
an
original
'glazing'
adhered
to
and came
off with
them, revealing
in
each
case
a
lighter
main
paint
layer
below,
and
that the
present
surface
of the
rest
of the
picture
is,
therefore,
not
a discoloured
varnish
but
the
original
'glazing
with
which
Gozzoli
had
achieved
his
final
colouring'.29
It is difficult
to
understand
how
the
removal
of wax
could
involve
an
underlying
glaze, since it is a simple operation to remove even old wax
without
in
any way
harming
underlying paint,
however
delicate.
If
any
substance
adhered
to and was
removed
with
the wax
its
presence
could
have
been
easily
demonstrated
by
chemical
tests
and
optical
examination;
no
such
evidence
is
produced.
In
point
of
fact,
however,
the
removal
of
the wax
drops appears
to
prove
the
contrary
to what
is claimed.
The
light
colours
revealed
by
their
removal
seem
to be
those
of the
original
finished
surface.
Support
for
this view
is
provided
by
other
drops
of wax
still
sticking
to
the
picture
surface.
These
appear
to
have
an accumula-
tion
of
the
supposed
glazing
round
their
perimeter,
which would
prove
at least
that
it is later
than
the
drops.
Further,
there
appear
through
the
semi-transparent
wax
of
the
surviving drops
what
seem
to be
the
lighter
colours
uncovered
elsewhere
by
removal
of
the
wax,
and
not the
duller
colours
of
the
'glazing'.
In other
words,
it seemsclear that the dropsof wax must have fallen on the picture
surface
before
the
application
of
a
varnish,
now
discoloured,
which
has
been
mistaken
by
Professor
Brandi
for
glazing.
It would
appear,
therefore,
that
the
facts
concerning
the
three
paintings
in
question
will
not bear
the
interpretation
put
upon
them,
and
lend
little
or
no
support
to
Professor
Brandi's
theory
of
'patina'.
*
The
MS.
sources
consulted
are:
Lucca
MS.;
Mapple
Clavicula;
THEOPHILUS:
Diversariumrtium
chedula;
ERACLIUs:
De
coloribus
artibus
Romanorum;
e
Beque
MS.;
S.
Audemar
MS.;
Mount
Athos
MS.;
Venetian
MS.
(Sloane
416);
Bolognese
MS.
(Segretiper
olori);
trasbourg
MS.;
Marciana
MS.;
Padua
MS. Printed
sources:
ALESSIO:
op. cit.
(1555);
FIORAVANTI:
op.
cit.
(1564);
BORGHINI:
op.
Cit.
(1584);
ARMENINO:
Op.
Cit.
(1587);
ROSSELLO:
op.
Cit.
(1575);
BIRELLI:
OF.
cit.
(16oI).
28
e.g.,
CENNINI:
Trattato
ella
Pittura,
hap.
155.
Adunque
ogli
a tua
vernice
liquida
lucida,
chiara
a
piCt
he
possi
rovare;
con a mano
i
distendiutta
questa
vernice
ottilmente
bene.
27
At the
period
n
question
only
oil varnishes
were
in
use.
28
The
photograph
eferred o
is
an
enlargement
x
31)
specially
made
by
Messrs
Anderson,
of
Rome,
from
their
negative
No.
Io8oI
taken
many
years
ago.
29
Owing
no doubt
to
the
difficulties
of
translation,
the
passage
dealing
with
this
picture
in Professor
Brandi's
article
as
published
(op.
cit.,
p. I88)
appears
to
convey
the
opposite
to
what
is
here stated
as
his
view.
The author's
true
intention
was
explained
by
him
in front of
the
picture
during
a
visit
of
the
Commission
for
the Care
of
Paintings
to
the Istituto
Centrale
in December
'949.
192
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