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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


8/11/2019 870432 info about MS

4/5

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


8/11/2019 870432 info about MS

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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