Comparative stratigraphy as an exact method of dating
works of art has its beginnings deep in the past and ivas
used, as in archeology, wherever attention was paid to
the place of deposition of works of art or historical
strata of alterations place upon them.
Sometime at the beginning of this century extensiv excavations
and restoration work was carried out in the Roman basilica
of Santa Maria Antiqua and in other places in Rome. From
the rubble and underground tombs they brought to the light
of day extensive and numerous remnants of early medievalpaintings,
often with one layer upon the other. By separating layer
from layer, analyzing them and making mutual comparisons
it gradually became possible to determine individual phases
of time and to reconstruct the development of the Roman
School of painting from the 5th to the 11th century. The
result of this pioneering work ivas summed up by Grüneisen
in the book St Maria Antiqua, published in Rome in 1911
1. Later work proceeded in similar
manner in Dura Europas 2.
The stratigraphie method was developed in the framework
of Christian archeology; in contact with classical archeology
the methods of stratigraphy on the terrain were applied
3. More recent examples
include the work of Kazimír Michalovsky at Pharas in the
sixties, a large part of which is shown in the National
Museum in Warsaw 4.
All the examples cited refer to the sphere of mural paintings,
where the stratigraphie method is clearest and most easily
comparable. It is obvious even to the layman that each
layer of plaster or coat of lime represents a certain
period of time and that it dates the laver below it relatively.
If the re search into strata is carried out with sufficient
thoroughness, the record of the sequence of layers of
plaster or lime dates not only the possible find of mural
paintings but even the architecture itself. The stratigraphie
record sets aside those parts of the architecture that
are additions to the original building, e.g. various enlargements,
additional parts etc. 5
Dating Possibilities of Overpaintings
Restorer's reports often include data on overpaintings,
their colours (quality), thickness and time sequence.
Rarely is sufficient attention devoted to them although
they can be a primary source for stipulating dating
ante quem. Such data do not always give forth witness
immediately but careful records and later confrontation
with other facts can acquire basic value as verification.
A classical example can be a group of statues that
apparently are compact and identical in style with only
insignificant differences in style. When later coats are
gradually removed it is, however, shown that the original
layer of polychromy of one statue is the overpainting
of a second. Result: the second statue is older than
the first, the group was made up secondarily as shown
in table A The number of stratus can be widened, in a more
numerous group there may arise more complex relationships,
hut the basis remains the sa me: by a method of elimination
of the record of stratus the relatively oldest origin
of one or other statue can be stipulated, possibly their
sequence in time. This is a current way of recognizing
later additions – hands, parts of the draperies, the pedestal,
etc. The restorer very often finds such relationships
in a stratified composition. The fragment of a group
of the Titrée Maries at the Tomb in the Museum in Polička
can serve as illustration of the simple relationship of
strata indicated, ne number of stratus found might have
con finned the preliminary dating of the sculpture to
the end of the 17th century. But on one of them – Magdalen
an older origin was stated. The light wax layer of ochre
colour forming the first coat of the garment of Mary forms
overpainting on Magdalen, covering even parts later adapted
by re-carving. In folk sculpture, in particular, where
written records usually are absent, consistent stratigrafie
research is often the only possibility for orientation
as to the time of origin.
We use the term stratigraphic to concur with terminology
used in archeology. It is now being used in work on mural
paintings. The archeologist uses stratigraphy as a record
of the individual cultural layers in a given locality
and regards the sequence as an exact proof of time sequence.
The art restorer can use a similar record of the
placing of individual strata of paint (over-painting)
and can stratigraphically date a given artifact.
For an archeologist rubble, chippings, alluvial deposits,
loess represent relative time strata as cultural layers,
and their deposition gives indication of relative time
sequence. For a restorer and for art historians who
gain information from him these traces of time sequence
are represented by the individual repairs to an artifact
carried out at different periods of time. They take the
form of renewal of coats of paint (or different overpainting),
new varnishing, mastic, additions, carving alterations.
The data on the sequence of layers of polychromy are of
equal relative value as the archeologist's stratigraphic
record. Not always is there something to base their interpretation
on: it requires long and exacting comparison to which
physical and chemical methods of research can contribute,
and not always is it possible to find possibilities of
comparison. As in archeology, the basis may be one single
fixed point, a historical record relating to one
of the stratas, or the identity or similarity of one stratum
to another, for which such a historical finn point
does not exist. And as was said at the beginning, there
is no alternative but to make a record of the sequence
and quality of each layer for interpretation at some future
The stratigraphie method of dating an artifact comprises
a) the record
b) the interpretation
The record is not always sufficient, and we should not
be content even with the best. Insufficient capacity for
carrying out chemical and other analyses should not discourage
us from amassing material (samples) for future use. Records
are kept of the sequence of strata, any striking marks
of different quality (be they in colour scheme, thickness
of application or different solubility) and it is of great
help to draw (record) the individual strata and their
interdependence into a graph (e.g. carnation, characteristic
samples taken of the draperies and other surfaces in the
case of sculpture). The more precise the record, the more
exact can be the resulting interpretation. The interpretation
comprises, in the first place, simple comparison of the
composition of strata between individual parts (the body
–» addition, sculptural group –» older or newer figure,
architecture –» additional part), on which parts added
later can be very precisely eliminated The following result
is achieved by comparison with historical data. Should
these data be indirect ones (which is most frequent),
the result has the value of hypothesis with more or less
probability. If the data are direct ones, definite dating
can he given. The importance of a precise record
of strata rests in the fact that most often historical
records refer to repairs of a given artifact (i.e.
one of the intermediate layers), and for that reason the
original strata can be dated with relative likelihood.
This, in fact, represents the current value of restorer's
reports for the terminus ante quem.
Values of high probability (which archeology normally
has at its disposal) can be achieved even without direct
historical records, by extensive comparative operations,
in particular when dealing with a larger set of artifacts-e.g.
furniture with works of art for which outline reports
exist (records of repairs, change of ownership, destruction
in wartime, etc.). These extensive comparative operations
will, in future, be carried out on the basis of physical
and chemical analyses even for artifacts that are more
remote in place and time. So far there are no conditions
for this. A prerequisite is systematic collection and
concentration of records and samples.
In the interpretation of stratigraphy mechanical addition
and elimination must be excluded, it can happen that a sculpture
of older origin has fewer strata than a later statue
that was more often painted. In other words, the number
of strata is not a reliable proof of relative age
unless upheld by the identity of the technical structure.
Identity here means full agreement of one stratum of a given
artifact with another stratum of a second artifact.
And again, as in archeology, all interpretations involve
dangerous drawbacks that can be avoided only by consistent
search and linkage of identity. This relationship is shown
graphically on table B. On the left side is the normal
composition of layers in polychromy of artifacts Ą, B,
C. Using mechanical comparison of the number of strata
object A might seem the youngest. But using the rules
of identity we reach a different stratification in
time drawn in the right-hand part of the table: the horizons
lead from the oldest at the bottom to the youngest at
the top, i.e. identical with the position of the strata.
The resulting interpretation is the following: the oldest
in time are objects A and C. In the second phase object
C was over-painted and object B was added to the group.
The third phase left its marks only on object B. The fourth
phase brought the first (and only) overpainting of object
Ą while object C was left in the state of phase 2 and
remained so until phase 5 when it was belatedly likewise
Two Maries (Magdalene on the right) from Polička, Municipal
Museum and Gallery
The example chosen is an extreme one. In normal practice
we can encounter such a situation on very rare occasions.
Most often repairs involve all parts of a given group,
and then the relations in time are far clearer. But there
are cases when not all time strata are kept, that all
gaps disappear if the older coat is scraped off during
repairs or is washed off, leading to accidental linkage
that will be explained below. Sometimes a group of
2-3 strata belong to one repair, one phase of time, or,
as the archeologists say, to one horizon. Associated strata,
as one might call this one-phase configuration, usually
contain a base anda coat of paint, sometimes a glaze
and their mutual comparison with individual parts of the
unit is more reliable in view of the multiplied clarity.
From a technical and artistic point of view these
associated strata tend to be of higher quality (reflexive
optical construction) and appear most often in older phases.
Later over-painting tends to be compact without transparency.
The chalk interlayer in later phases usually fulfils merely
a function of ground and mastic without sufficient
optical use. The method involves an element of checking.
It has become a rule that by removing subsequent
overpainting a block of the removed strata is left
for analysis as orientation and a dating feature
not dependent on the availability of restorer's reports.
Sequence, Conjunction, Record
The time horizons in table B are marked with dotted lines.
These time horizons are imaginary lines separating the
stages of individual repairs and they are immensely important
for the distinction succession (sequence) and con tact
(conjunction) of strata.
A mere conjunctions of strata can occur in the cases cited
when part of the historical measures were removed before
newer coats were applied. Every restorer knows from experience
that all layers are not to be found on every place. The
chemist who tests a given section of an accidentally
chosen spot of the painting or polychromy tests only the
local conjunction, which might lead to a mistake.
Only the restorer that, in the process of work, tests
the whole work or group of artifacts can reach an overall
interpretation on the basis of his observations, i.e.
can give a real description of the sequence of strata.
The same applies to the description of painting technique,
i. e. from our point of view in the interpretation of
one time horizon. The carnation of one syncopic and reflexive
composition can serve as example. Samples that were taken
from various places show different sequence and composition
of paint layers - along the edges were seen reliefs of
shadow, in lit up parts coats of white were applied. The
patterns differ in conjunction. Sequence has to be explained
The sequence of repairs of larger sets (e.g. altars, epitaphs)
is that of interpretation and description. More than 40
samples taken from an epitaph in Most (Northern Bohemia)
did not give a single complete sequence of strata.
Sequences are looked for also during research into layers
of plaster, for in architecture the application of later
strata is often preceded by the removal of older layers.
Simple conjunction is often confusing. But in seeking
identities a very precise relative chronology can
be attained. The research into mural decorations of the
chateau at Holešov brought rich material for this method.
On the basis of numerous probes, their mathematical and
graphic record and final evaluation it became possible
to date some of the finds with relative precision, some
strata could be dated directly, and, at the same time,
certain mistaken dating was corrected after having been
used in literature. The result is the table that depicts
the time horizons and their expression in individual rooms
of the castle.
This method was earlier applied in research into the furnishings
of the Church of John the Baptist at Velký Bor (Klatovy
district). It had as result explanations for the colour
scheme of the furniture in seven basic time phases, which
simultaneously reflected certain changes in aesthetic
attitude to the colour setting. On the side altar of the
Virgin Mary there were identified remnants of an originally
larger high altar, dating from the Renaissance, which
included in its centre a Gothic statue of the Madonna
from the early 15th century. In the extension of the later
high altar were identified two Renaissance heads of angels.
These examples from my own experience are representative
of many other investigations that restorers have in recent
decades carried out and which – withcertain variationsin
method- regularly extend the limits of our knowledge of
technical development further afield.
Possibilities of Interpretation in Future
Precise terminology and precise data are essential for
the interpretation of our partial discoveries to be adopted
and used. Research during each restoration brings facts,
either direct or as analogy to a work of dating.
Some can be exact and irreversible, others can serve as
a point of departure (supporting point) today or
in the distant future. The record needs to be precise
to a maximum. That is the purpose of the Archives
of Historical Art Technology that gathers, classifies
and publishes study material. Our field is at present
in the state that archeology found itself in the initial
phase of development when scholars were working with a variety
of methods and used different terms to refer to identical
facts. We need to record the results of our work, make
terminology more precise; like the archeologists we need
to »draw the pots« and place them in the archives. We
must reckon on the results of our work being used in twenty
or even fifty years. Archeologists know no other perspective.
And thanks to that patience and to careful records of
any and all facts and observations archeology has attained
its present syntheses.
The precision of records facilitates better communication
with art histarians whose interpretation is no longer
possible without technological analysis. As is clear from
what has been said, the search for the date of origin
of a work of art is not the most fundamental matter.
It is more an imaginary unattainable line towards which
individual operations are directed: it is a moving
force that helps refine the method and make the knowledge
of historic truth more precise.
But from exprience we know very well that such concurrence
cannot be achieved immediately and that our practical
work is likely to be accompanied by open problems. But
there is no other way out if we do not wish to remain
on grounds of mutually hidden empirical knowledge. It
means constant discussion in an open atmosphere, with
the right to risk, the right to mistakes that can later
be withdrawn. For as our knowledge advances, with the
aid of numerous series of comparative analyses the scientific
media we use will gradually become more sophisticated
There can be little doubt that we shall see the individual
historical horizons far more clearly in future.
Antonín Novák, AHVT A 015 (T.G.)
1 W. de Grüneisen, Sainte Marie
Antique, Rome 1911
2 Marcel Aubert, in: Rostovtzeff-Brown-Welles:
The Excavations at Dura Europos (Preliminary Report of
the 7th and 8th Seasons of the Work – 1933/4 and 1934/5),
3 The pioneering work of Professor Cibulka should
be recalled, the work of the Prague Seminary of Christian
Archaeology of the Faculty of Arts of Charles University,
the Kondakov Institute, etc. A large pan of the libraries
of these institutions has survived thanks to the Department
of Art History at Charles University. Worth mentioning
also is an »analytical method« of conservation, especially
in architecture, favoured not only during the First Czechoslovak
Republic, but earlier in the case of St Vitus Cathedral.
In the work ofV. Birnbaum (reedition cited above.) an
exact application of archeological methodology of its
time (St George's Basilica) was explained.
4 K. Michalowski, op. cit. But characteristics
of the paintings in the catala gue lacks restorers' analyses
– the description of the stratified structure, which is
a necessary further stage of the method developed.
5 The method of a thorough record of strata
was applied with exceptionalresults in restorer's research
on houses on the square at Jihlava (no. 39, 47, 50-51,
66-67), carried out in 1981-89 in collaboration with the
Regional Centre for the Care of Ancient Monuments in Brno.