The Mona Lisa Foundation

Analysis of the Materials used in the ‘Earlier Mona Lisa’


The Canvas Support

The main characteristics of the linen canvas used for the earlier version portrait were straightforward: plain tabby weaves with an average thread count of 18 threads per cm warp, and 16 threads per cm weft, crossing each other of course, and with some variations in thickness. The result is a warp that is slightly tighter than the weft. That Leonardo would choose available canvas instead of a wood panel upon which to paint a portrait is really not that surprising. One of the major criticisms put forward against the Leonardo attribution of the ‘Earlier Mona Lisa’ to Leonardo relates to its canvas support. However, when the matter is examined in detail, it is easily put to rest.

The support, which has a tight warp and a loose weft, is made of linen cloth. The coarse and irregular weave are indicative of a hand-woven canvas.

Drapery study for a Seated Figure. Oil on canvas, c. 1475-1480, Leonardo da Vinci.

Leonardo had Worked on Canvas

Leonardo executed a number of works on canvas while working under Verrocchio in the 1470s. It is no coincidence that the drapery studies that Leonardo painted on canvas roughly 30 years earlier, and that are now in the Louvre, display almost identical characteristics to those of the earlier version. As with the ‘Earlier Mona Lisa’, these canvasses of course were also naturally hand-woven.

Historical Context

The turn of the 16th Century marked a significant period of transition in the use of artists’ materials. Knowledge about the use of new media from advanced Flemish and Venetian masters was becoming more widespread. Oil and artificial pigments were starting to become popular: in fact Leonardo was using oil as a binder and medium as far back as his time as a student of Verrocchio. Up to the 16th Century, wood was the most popular support for painting, and prior to 1470 almost nothing of importance in Western art was painted on canvas. Leonardo’s ‘Lady with the Ermine’ and ‘La Belle Ferronniere’ were painted on walnut panels. The Louvre ‘Mona Lisa’ on the other hand, was painted on poplar, a wood more frequently found in Lombardy than Tuscany.

Canvas was, by 1500, already in use by painters in Italy. It is known that c.1499-1500 Leonardo visited Venice via Mantua, on his return to Florence after his sojourn in Milan. In Mantua, he would likely have met with Andrea Mantegna, the Court Painter for Isabella d’Este at that time. Mantegna was a great exponent of painting on canvas, and might well have influenced Leonardo. Vittore Carpaccio, from Venice, is also of particular relevance, as he was of the same age and lived during the same times as Leonardo as did Giorgione. It is considered that Leonardo collected some new ideas from Venetian masters, certainly about the use of glass in pigments, in addition to the use of canvas as a support. All of this occurred just before he set to task on Mona Lisa.

It can clearly be seen that from and subsequent to Leonardo’s working life, the use of canvas as a support was coming into greater use: not just with Dutch and Venetian masters, but also with Germans, Florentines and other Italians. There is also well documented evidence of masterworks Leonardo’s contemporaries some of whom, as stated above, he would have been in direct contact, including:

• Sandro Boticelli (1446-1510)
The Birth of Venus’, c.1482-1485 (Florence)

• Giorgione (1477-1510)
The Tempest’ c.1508 (Venice)

• Andrea Mantegna (c.1431-1506)
The Holy Family with St. Elizabeth and the Young St. John’, c.1498-1499 (Dresden)
The Mourning over the Dead Christ’, c.1501 (Milan)

• Raffaello Santi (Raphael) (1483-1520)
Lady with a Unicorn’, c.1504-1505 (canvas, transferred to panel)(Rome)
The Sistine Madonna’, c.1516 (Dresden)
Portrait of Count Castiglione’, 1515 (Paris)

• Tiziano Vecellio (Titian) (1488-1576)
La Bella’, 1536-1538 (Florence)
Ecce Homo’, 1543 (Vienna)
Portrait of the Artist’, c.1565 (Madrid)

• Vittore Carpaccio (c.1455-1525)
St. Ursula’s Arrival in Cologne’, 1490-1495 (Venice)
The Blood of the Redeemer’, 1496 (Udine)

• Tintoretto (Real name: Jacopo Comin [a.k.a. Jacopo Robusti]) (1518 -1594)
The Erection of the Cross of the Repentant Thief ’, 1565 (Venice)

Leonardo the Experimenter

One cannot forget that Leonardo was not only a great inventor and innovator, but he was continually experimenting with new ideas and technology. It is timely to note that a small work of art executed on vellum in the early 1490s has recently been authenticated as a Leonardo. This is particularly noteworthy as Leonardo had not been known until now to have produced any finished work on that material, before or since. In his book La Bella Principessa, Martin Kemp writes “It shows him utilizing a medium that has not previously been observed in his ‘oeuvre’, but one that relates closely to his interest in the French artist Jean Perreal. It testifies to his spectacular exploration and development of novel media, tackling each commission as a fresh technical and aesthetic challenge.”

There is every reason to believe, given Leonardo’s inquisitive nature and the historical context that he would certainly have experimented with canvas at the turn of the 16th Century. The drapery studies are also particularly relevant, as they emphasise Leonardo’s classical concerns for accuracy in rendering the folds of clothing, and how they can reveal the human anatomy beneath.

Leonardo wrote about how to paint on Canvas

Though the foregoing suggests that it would be no surprise that Leonardo used a canvas support for some of his works, one fact pretty well confirms beyond reasonable doubt that he did. In his Treatise On Painting Leonardo describes in detail not only how to prepare canvas for painting, but also how to paint on it. Modo Di Colorir In Tela (How to paint on canvas) – CAP CCCLIII.

Leonardo sets down the basic instructions: “Stretch the canvas onto a chassis, then apply a light coat of fluid glue and let it dry. Then draw your painting with tone using silk brushes adding, in your style the “sfumato” technique to place the shadows while the paint is still fresh. The complexion is made-up of white of ceruse lacquer, and Flanders yellow; the shadow will be made from black, burnt umber and a little lacquer, or if you prefer, a hard pencil. After completing the “sfumato” let the work dry; then do dry retouches with a solution of diluted lacquer in gum arabic that has been left a long time. The longer the mixture is left the better the result, as it remains matt. If you want your shadows darker, take the same gummed lacquer, adding ink. You can use this mixture to shade numerous other colours including azurite, lacquer, etc., because it is transparent. I have stated for the shadows, now for the highlights you can make tints from using a simple gum arabic lacquer over the top of undiluted lacquer and over this is applied a diluted veil of dry cinnabar.”

Now this description is key for two reasons. First, it demonstrates unquestionably that Leonardo did paint on canvas. All of this knowledge was gathered through real life experiences and experiments and it would be simply impossible to believe he would describe the details of a process he never executed himself. Second, the level of detail in which he describes the process is strongly suggestive that his use of canvas extended beyond simple studies. This implies that there would be major works by Leonardo, such as the ‘Earlier Mona Lisa’, that were executed on the material. It is believed that about half of Leonardo’s paintings may still be missing or still to be correctly attributed. Given the above, it is quite likely that a number of these works were executed on canvas support.

Another extremely important point relating to the ‘Earlier Mona Lisa’ is that its very existence on canvas instead of a wood panel belies any suggestion and is just one more piece of evidence against the idea that it could ever have been a ‘copy’ of the Louvre version, or vice versa. Clearly, and as is discussed in detail in the section about comparisons, Leonardo would have intended to make two different versions. Furthermore, if Leonardo was considering an opportunity for his earlier version to be in any way experimental, especially in content or composition, then it is most credible that he might have used canvas as a familiar and convenient material.

 

See above image of canvas detail, taken from this edge of the painting.

The Lining

It is a common technique with very old paintings on canvas to reinforce the original support by attaching it to a new second canvas or lining. This process not only strengthens the original support, but assists greatly in the overall preservation of the picture. In the case of the ‘Earlier Mona Lisa’ this attachment was executed by means of a glue mixture: a combination of flour paste, gum and Venetian turpentine as plasticizer. In certain lights, this produces a slightly uneven surface – a difficulty later overcome by the subsequent process of hot table-wax lining.
 

A technical examination of the painting shows that the original canvas was very slightly trimmed when it was attached to the lining, but the raw edges of the original paint have not been touched. The new lining is a manufactured fabric of uniform plain tabby weave, with an average count of 14 threads per cm for the warp, and 14 threads per cm for the weft. This is the canvas now visible on the back of the work. It was attached to the stretcher with nails. As there are no holes from prior nails in the lining, one can surmise that the present stretcher was put into use when the painting was lined. The pattern of the canvas appears slightly wavy along some edges, due to irregular degrees of tautness when it was attached to the original stretcher.

The Stretcher

This is the wooden frame upon which the canvas has been made taut. The one seen at the back of the ‘Earlier Mona Lisa’ today is a replacement for the original stretcher. The corners of the lining canvas have been cut back to correspond with the original canvas, the edges glued and then trimmed on the stretcher. This likely would not have been the case if this was the original wooden framing stretcher.

The lining is now fixed according to the actual dimensions of the painting, and the wooden wedges inserted at the four corners give the canvas maximum tension.

The Ground

The base ground layer is composed of a combination of red-brown ochre and calcite, with some grains of quartz. This colour as a base, allows to bring out a sense of warmth across the whole painting, where the colours are predominantly earth-tones on the hand-woven canvas. Significant in the painting’s inherent beauty is the conspicuous lack of any strong polychromatic colour: all the elements are in organic harmony, and help to accentuate the gorgeous skin tones. Part of the reason for this is the reddish-brown undercoating.

There is also evidence for this approach in other famous Leonardo portraits. Over the space of two years, from 1952 to 1954, his ‘Lady with the Ermine’, underwent scientific and technical examination at the National Museum in Warsaw. There it was revealed that the background of the painting consisted of a combination of ivory black, earth of burnt umber and natural sienna. Another probe, on the subject’s dress, revealed that the pigment had to be of a ferruginous origin.

La Belle Ferronniere’, also underwent laboratory testing at the Louvre in the early 1950s and again quite recently. Professor Pietro Marani, in his 2003 book, Leonardo da Vinci – The Complete Paintings refers to Sylvie Beguin, the distinguished Conservateur-en-chef there, who noted: “The laboratory exams reveal a pictorial surface which is thin and a preparatory ground of red earth very close to Leonardo’s technique.” The most recent analysis showed that the painting contained a significant amount of Calcium Carbonate.

Professor Marani subsequently refers to the Louvre ‘Mona Lisa’ as follows: “… Examination under a microscope reveals at least two colours in that preparatory ground: blue under the upper, landscape part; red under the lower part. Leonardo used the same two-toned ground in ‘La Belle Ferronni่re’, ‘The Musician’, and ‘St. Anne’.

In addition, a recent report in the National Gallery Bulletin states that the Prado ‘Mona Lisa’, which is believed to have been executed by one of Leonardo’s assistants, also displays a coloured reddish ground.

The American conservation scientist H. Travers Newton, was, in 1974, making a technical enquiry under Vasari’s frescos in the Palazzo Vecchio in Florence to try and locate any remnants of Leonardo’s ‘Battle of Anghiari’. The process employed was Thermavision – an infra-red Vidicon system, super-cooled with liquid nitrogen – in order to probe the walls. This equipment produces a thermal map of materials present beneath the surface: different materials absorb and emit heat at different rates. According to Charles Nicholl: “All the core samples showed a layer of red pigment beneath Vasari’s ‘intonaco’, and some showed other pigments laid over this red ground. These included two suggestive of Leonardo’s practice – a green copper carbonate similar to that used in the ‘Last Supper’, for which Leonardo gives a recipe in the Trattato; and blue smalt, as found in the Louvre ‘Virgin of the Rocks’ … Azurite was also found, which is not suitable for use in true fresco, so it suggests the anomalous area is not a conventional fresco.”

This comment highlights at least two separate issues. Firstly, regarding Leonardo’s fresco work, and some of the reasons his two major fresco commissions ended badly: a rash enthusiasm for experimentation with both oils (in the ‘Last Supper’) and encaustic materials (‘The Battle of Anghiari’) while eschewing the traditional tempera methods.

Secondly, the prevalent use of a red ground for the Anghiari fresco would have occurred at exactly the same period as the application of red ground on the ‘Earlier Mona Lisa’. The two commissions would have coincided, so it is logical that his palette would have been similar at the time. Traces of smalt and azurite, similar to the findings of Travers Newton, are found in the background landscape of the ‘Earlier Mona Lisa’.

In 1998, at the Dublin Congress of the International Institute for Conservation of Historic and Artistic Works, Jill Dunkerton and Marika Spring of the National Gallery, London, presented further relevant information: “With reference to tinted and coloured preparations, from light to mid-tone, the thin pigmented layers found immediately above the gesso may in fact be monochrome undermodellings of the type seen on unfinished pictures by artists such as Leonardo da Vinci and Fra’ Bartolommeo, rather than primings … Nevertheless the number of works with tinted and moderately coloured primings … is considerable and includes as many panels as canvasses.”

This priming technique was also practiced by numerous contemporaries of Leonardo, including Antonio Allegri da Correggio, Dosso Dossi, Alessandro Bonvicino (Moretto da Brescia), and his student Giovanni Battista Moroni. These painters were popular and prolific in their time, and seriously underrated by Vasari. The impression of an artist experimenting with a variety of preparation is supported by the discovery that Correggio’s large canvasses, ‘Venus with Cupid and Mercury’, and his ‘Danae’ in the Borghese Collection in Rome, have a thick red-brown priming based on red earth. Stylistically, the overt sensuality of Correggio’s paintings contrasts with Leonardo the Florentine’s subtle implications. Dunkerton and Spring have also pointed to the relevance which dark preparations offer for a more rapid and direct execution of the painting. Furthermore, the gray prime coat found in so many Italian paintings of that period corresponds to all the sample probes taken from the ‘Earlier Mona Lisa’.

It can therefore be clearly established that the reddish-brown ground on the ‘Earlier Mona Lisa’ is compatible with some of Leonardo’s other significant paintings. This ground colour could be seen as a signature of the master’s creativity and knowledge of pigments in overcoming challenges to present the colours of the final layers as they should be correctly seen by the naked eye. Leonardo’s extensive use of reddish-brown ground can also be noted in his drawings and studies, some of which are in the Royal Library at Windsor, and in the Uffizi in Florence.

The next layer, which is grey with a slight purplish hue, consists of calcite, lead white and bone black. Again, the colours specified above, by Leonardo in his Treatise, are in full use on this portrait. Charles Eastlake states: “ … there is scarcely a picture of Leonardo, whatever stage of completion it may have reached, which does not exhibit this more or less solid purplish preparation, varying from an ink colour scarcely removed from grey.” Eastlake also discusses the treatment of application of the pigments. In relation to Leonardo’s technique he writes: “This thinner use of the opaque colours was still more requisite in the half-lights, the varieties of which chiaroscuro had already been expressed in the grey or purple preparation with the utmost nicety: on these therefore, the scumbling colours, tending to harmonize the subdued lights with the rest of the work, were spread with a sparing hand, softening still more the finer markings rounding the forms by almost imperceptible graduations, or as Lomazzo expresses: With tinted film upon film … Sfumato!

Larry Keith and Ashok Roy in their bulletin Giampietrino, Boltraffio, and the Influence of Leonardo, 1996, write: “In Leonardo’s paintings an overall pictorial unity produced by a tightly controlled, restricted range of tone and value was a central feature. The sculpture-rivalling relief of the National Gallery’s cartoon of the ‘Virgin and Child with St. Anne’ and ‘St. John the Baptist’ (NG 6337), with its severely restricted palette, illustrates Leonardo’s primary concern with the creation of depth through the manipulation of value, not colour. In painting, while he did develop the techniques of exploiting colour of diminishing intensity to create aerial perspective, the intrinsic beauty of certain naturally high-key pigments was as a rule deliberately and consistently subordinated to the constraints of his greater tonal discipline.

Most striking is Boltraffio’s use of a dark underpainting (‘The Virgin and Child’) of some solidity for much of the composition, and this seems to have been a key part of Leonardo’s method, and can be seen in a number of unfinished works (e.g. ‘The Penitent of St. Jerome’ and the ‘Adoration of the Magi’) [Note: Boltraffio was an early student of Leonardo and worked in his studio around the 1490s.] Leonardo used often a dark mixing oil in all the layers including a dark undermodelling.

Paint Pigments

In his Treatise On Painting, in the chapter How to Paint on Canvas – CAP CCCLIII, Leonardo sets down the basic instructions, and some of the pigment described can be found in the ‘Earlier Mona Lisa’: “Stretch the canvas onto a chassis, then apply a light coat of fluid glue and let it dry. Then draw your painting with tone using silk brushes adding, in your style the “sfumato” technique to place the shadows while the paint is still fresh. The complexion is made-up of white of ceruse, lacquer, and Flanders yellow; the shadow will be made from black, burnt umber and a little lacquer, or if you prefer, a hard pencil. After completing the “sfumato” let the work dry; then do dry retouches with a solution of diluted lacquer in gum arabic that has been left a long time. The longer the mixture is left the better the result, as it remains matt. If you want your shadows darker, take the same gummed lacquer, adding ink. You can use this mixture to shade numerous other colours including azurite, lacquer, etc., because it is transparent. I have stated for the shadows, now for the highlights you can make tints from using a simple gum arabic lacquer over the top of undiluted lacquer and over this is applied a diluted veil of dry cinnabar.

Occasionally artists would paint directly onto these gesso grounds: in many instances the ground was modified by the application of layers intended to reduce its absorbency. Such a coating over the gesso is called in Italian an imprimitura, often referred to in English when writing on Italian painting techniques.

The author Stuart Fleming refers to this base gesso as a ground, instead of it being called the initial preparation of the canvas. The ground coats are really layers of pigments laid down over the gesso, to assist in building-up the subsequent layers of paint colours, both opaque and transparent, to create the desired effect.

Two series of analytical probes were effected on the painting primarily in order to identify the complete range of pigments and other media used, as well as to help ascertain some of the techniques he employed in the preparation of the canvas support, and the application of the base, ground and paint layers. The results not only identified the pigments and other material, but also pointed to the sequence in which sections of the work were undertaken. Dr. Hermann Kuhn’s nine probes were taken in June 1977, and it was in June 2005, exactly 28 years later, when Dr. Maurizio Seracini dated the results of his further 10 probes. The results are listed chronologically. It is acknowledged that there could have been some procedural advances during those 28 years, and the intention here is to be as comprehensive as possible.

Except for his first probe, which goes to the lowest base layer, Dr. Kuhn’s report primarily specifies the surface pigmentation in each case. Dr. Seracini’s probes identify the pigment material in every layer of each probe. Naturally, there cannot be any direct comparison between the results, as each probe was taken from a different part of the painting.

Location of the 19 samples taken for pigment analyses.

First analysis: Dr. Hermann Kuhn

Probe #1: Flesh pigment

The lowest layer is a red to red-brown base that is composed of red-brown ochre and calcite, and includes a few bigger grains of quartz. There is a subsequent grey layer of base consisting of calcite, lead white and bone black. This is covered by the flesh layers which contain lead white, calcite, a few grains of black vermilion, zinnober* (HgS – Mercury sulphide), vermilion, and yellow ochre.
[*Editor’s note: this is what Leonardo refers to as dry cinnabar]

Probe #2: Dress, brown pigment

On analysis it was found to contain brown iron oxide of manganese umber, vegetable black, lead white, calcite, and red lacquer.

Probe #3: Mountain, yellow highlight pigment

Two tests were made on the yellowish to greenbrown layer that contained the total of pigments present. It contained vegetable black (powder of charcoal), smalt, blue copper pigment apparently made artificially with copper blue – called veriter, azurite in little traces, transparent yellow, brown and red grains of iron oxide (burnt green, earth or earth sienna), yellow lacquer, calcite, lead white, and a large quantity of uncoloured glaze.

Probe #4: Tree, green pigment

Large grains of blue pigment in a yellowish brown binding. The analysis shows azurite in large quantities, smalt, and grains of lead white. The impression of green is given by an unidentified yellow (vegetable pigment). On reanalysis of this unidentifiable yellow it was found that there are not any yellow pigments except the presence of impurities of iron oxide.

Probe #5: Sky, pigment

Two paint samples were taken from different areas of the sky. Under magnification it is revealed that the two samples contained calcite, lead white, and a large amount of smalt, which has a fine grain and a very pale colour. A large part of the pigment looks colourless.

Probe #6: Dress, light brown pigment

The following components were found: brown iron oxide of manganese-umber, yellow ochre, lead white, little traces of red lacquer, and bone black.

Probe #7: Left background, red-brown pigment

It contains a mixture of yellow and red iron oxide (ochre and earth sienna), vegetable black, smalt, calcite, lead white, green earth, and artificial copper blue called veriter.

Probe #8: Dress fold, yellow highlight pigment

Contained lead white, calcite, yellow lacquer, yellow iron oxide (ochre), and vegetable black.

Probe #9: Left tree, dark green pigment

Over a grey-blue layer is a layer containing large grains of smalt and azurite, plus little traces of lead white, and calcite. The very dark tone is caused by an overlaying brown layer – (vegetable pigment), originally yellow-aged and/or yellowed varnish.

Second analysis: Dr. Mauricio Seracini

Probe #10: Dress

Layer 1: Red ground of earth pigments, natural ochres, lead white, minium, bone black, carbon black, smalt.
Layer 2: Grey layer priming of lead white, calcite, carbon black, and granules of red ochres.
Layer 3: Layer of carbon black, lead white, and umber.
Layer 4: Dark grey layer of carbon black, umber, and lead white.
Layer 5: Thin grey layer of calcite, and carbon black.
Layer 6: Dark layer of calcite in a rich binding medium.
Layer 7: Carbon black, calcite, and lead white.
Layer 8: Varnish
Layer 9: Glaze of carbon black.
Layer 10: Layer of varnish.
Layer 11: Layer of low-fluorescent varnish.

Probe #11: Edge of pillar

Layer 1: Red ground matrix of earth pigments, incl. lead white, minium, particles of carbon black, and bone black.
Layer 2: Grey priming layer of lead white, calcite, and carbon black.
Layer 3: Lead white and partly-decoloured smalt.

Probe #12: Tree

Layer 1: Red ground of earth pigments, lead white, minium, particles of smalt.
Layer 2: Grey priming coat of lead white, calcite, carbon black, granules of red ochre.
Layer 3: Lead white and decoloured smalt-blue.
Layer 4: Azurite and lead white.
Layer 5: Varnish.

Probe #13: Mountain

Layer 1: Red ground of earth pigments, lead white, minium, particles of carbon black, and bone black.
Layer 2: Grey priming coat of lead white, calcite, and carbon black.
Layer 3: Thin brown layer of lead white, calcite, and carbon black.
Layer 4: Green-blue pigments, plus brown-green layer of lead white, earth pigments, and umber.
Layer 5: Double layer of varnish.

Probe #14: Edge of tree

Layer 1: Red ground of earth pigments, lead white, minium, particles of carbon black, and bone black.
Layer 2: Grey priming coat of lead white, calcite, and carbon black.
Layer 3: Brown layer consisting of lead white, carbon black, calcite, earth pigments, and traces of smalt.
Layer 4: As ‘layer 3’ above, plus azurite.
Layer 5: Decoloured smalt, lead white, and earth pigments.
Layer 6: Green/yellow layer of earth pigments, yellow lake, plus green/blue pigment.
Layers 7-9: Three layers of varnish.

Probe #15: Sleeve

Layer 1: Red ground of earth pigments, lead white, minium, particles of carbon black, and bone black.
Layer 2: Grey priming coat of lead white, calcite, and carbon black.
Layer 3: Light brown layer consisting of lead white, calcite, earth pigments, particles of umber, and yellow lake.
Layer 4: Beige layer of lead white, calcite, and earth pigments.
Layer 5+: Several layers of varnish.

Probe #16: Chest

Layer 1: Red ground of earth pigments, lead white, minium, particles of carbon black, and bone black.
Layer 2: Grey priming coat of lead white, calcite, and carbon black.
Layers 3 and 4: Two layers of white, consisting of lead white, vermillion, and a few granules of carbon black.
Layer 5+: Several layers of varnish.

Probe #17: Hair

Layer 1: Red ground of earth pigments, lead white, minium, particles of carbon black, and bone black.
Layer 2: Grey priming coat of lead white, calcite, and carbon black.
Layers 3 and 4: Two layers light brown, of lead white, earth pigments, umber, and bone black.
Layer 5: Particles of decoloured red lake.
Layer 6: Several layers of varnish.

Probe #18: Pillar

Layer 1: Red ground of earth pigments, lead white, minium, particles of carbon black, and bone black.
Layer 2: Grey priming coat of lead white, calcite, and carbon black.
Layer 3: Brown layer of lead white, calcite, and earth pigments.
Layer 4: Black layer of lead white, carbon black, and earth pigments.
Layer 5: Paint layer – colour unspecified.
Layer 6: Brown layer of calcite.
Layer 7: Black layer of carbon black, small quantities of lead white, calcite, and earth pigments.
Layer 8: Thin layer of brown organic material.
Layer 9 +: Several layers of varnish.

Probe #19: Landscape

Layer 1: Red ground of earth pigments, lead white, minium, particles of carbon black, and bone black.
Layer 2: Grey priming coat of lead white, calcite, and carbon black.
Layer 3: Brown layer of decoloured smalt, lead white, and earth pigments.
Layer 4: Green layer of lead white, earth pigments, green/blue pigment, and granules of smalt.
Layer 5: Organic brown glaze.
Layer 6: Thin layer of lead white, and earth pigments.
Layer 7 +: Several layers of varnish.

The results of the foregoing analyses indicate that all the pigments that were found were already available at the commencement of the 16th Century.

It must be noted that in light of the invasive nature of extracting probes, it was advised and decided not to extract materials directly from the subject’s face. This decision was taken as it was confirmed that a probe taken from the face would most likely yield identical to those taken on other parts of the subject’s flesh (i.e. probes #1 and #16.

Leonardo’s ‘Mona Lisa’ Palette

A comparison of the pigments used in the two Mona Lisas brings interesting results. Lead white, for example is an important constituent of both. Regarding the ‘Earlier Mona Lisa’, both Dr. Kuhn and Dr. Seracini found lead white in every single probe, including the grey second ground coat. The Louvre report on their ‘Mona Lisa’ states simply that lead is present everywhere in the form of lead white.

Other pigments that are common to both paintings include azurite, blue copper, vermilion, umber and even smalt. In fact both pictures feature significant amounts of earth pigments such as the various ranges of siennas, ochres and umbers; natural enough for a time before the development of artificial pigments. There are variations as to how black pigments are referred.

Burnt umber, an earth-tone used in both paintings, has wonderful mineral properties: “One may therefore suppose that natural burnt-umber, or an earth pigment rich in manganese oxide, plays an important part in achieving Leonardo’s famous sfumato effect. The relative absence of cracks in the shadows of the face can be related to the drying properties of this pigment, which no doubt originated from Umbria, a region that is also famous for the quality of its earthenware.”

Traces of smalt were found exclusively in the background landscape of the ‘Earlier Mona Lisa’. Its popularity in artist’s pigments really only took-off in the second half of the 16th Century; however according to senior scientists at the Centre de Recherche et de Restauration des Musees de France (C2RMF) the use of smalt in easel painting was well known, though to a more limited extent in the second half of the 15th Century. Pascal Cotte of Lumiere Technology in Paris, who has examined Leonardo’s ‘Joconde’, ‘Lady with the Ermine’, and the ‘Earlier Mona Lisa’ concurs and states that smalt was well in use at the beginning of the 16th Century, and it is noted by the Louvre in the analysis of its Mona Lisa to be abundantly present.

A problem that many artists of that time had to face was the lack of ready availability of the pigments they required. Grinding minerals and earth-pigments with the correct media, to the right consistency and shade was a laborious and therefore expensive process. Many of these pigments “ … being imports as far as colour-merchants in the principal art centres of Italy, the Netherlands, France and England were concerned, were expensive and not always so readily available. Consequently, we can imagine that artists were eager to learn of any man-made pigments that could serve as alternatives to the traditional palette.”

In the extract from Leonardo’s Treatise above, there is a reference to “ … a diluted veil of dry cinnabar … ” This exists on the ‘Earlier Mona Lisa’, noted as ‘zinnober’, in a probe of one of the flesh tones, but is not mentioned for the Louvre ‘Mona Lisa’. That painting shows a small amount of vermilion in some of the flesh tints, as does the ‘Earlier Mona Lisa’. Leonardo cited red lac, or lake as the correct pigment for shadows and light areas. Again, both paintings show traces: on the face of the younger woman, and on the hands of the Louvre ‘Mona Lisa’.

In other chapters of his Treatise, Leonardo frequently refers to the use of lake, or red lake, particularly for flesh tones: “L’incarnatione fara biacca, lacca, e giallolino: l’ombra fara nero, e majorica, e un poco di lacca, o vuoi lapis duro.” (“The flesh colour may be made with white, lake, and Naples yellow. The shades with black umber, and a little lake; you may, if you please, use black chalk.”).

The authors of the great volume, Mona Lisa – Inside the Painting have admitted in the book that quotations and analyses from Leonardo’s Treatise concern painting on canvas. In a way, this is an oblique though fair acknowledgement that Leonardo would have had substantial experience with that material, and confirms that not only did he use canvas extensively, but executed significant works on it. To be even-handed, it is also reasonable to assume that, given the correct preparations, any of his formulas for painting on canvas could be configured, perhaps in different combinations, to be equally effective on wood.

The comment in the publication also highlights an issue that until now has rarely been tackled: a comprehensive study of Leonardo’s work on canvas. Elisabeth Martin, Naoko Sonoda, and Alain Duval comment: “All the major studies and articles on the preparation and pigment compounds of paintings of the Renaissance period in Italy, and particularly around Leonardo’s years, relate to paintings on wood only, and till recently little or nothing was studied on Leonardo’s works on canvas or other surfaces.” Certainly after the intense examinations undertaken on the ‘Earlier Mona Lisa’, one could gain a new understanding of Leonardo’s working techniques.

Interestingly with this painting, there are really no surprises: it fits with Leonardo’s own detailed and comprehensive directions, as he outlined both in the voluminous writings and reports assembled throughout his life, but also specifically in his Treatise On Painting, required reading for any true artist and student of Renaissance painting. No other artist of his time left such a wealth of information, either about his particular vocation, or useful instructions on how to achieve superlative results.

Dating

A) 210Pb measurement by gamma spectroscopy on a Lead White sample

This test is valuable in identifying the nature of lead-white, which can indicate if the artwork was executed more than 250 years ago. If the carbon content is completely decayed, the work was executed more than 250 years ago. To detect the presence of 210Pb radioisotope, the Lead White sample 7 was analysed with a Gamma Spectrometer for 278 hours, with a high resolution and low noise detector GX-HP Ge (ORTEC).

 

1 – Red ground layer of earth pigments. Lead White, Minimum, and some particles of Carbon Black. 2 – Gray layer of Lead White, Calcite, and Carbon Black. 3 – White layer of Lead White, Cinnabar and Carbon Black. 4 – Layer of varnish.

A Radioisotope is considered totally decayed when 12 t1/2 are passed. The data show that all 210Pb isotopes present in the sample analysed were completely decayed. Since 210Pb has a t1/2-20.4 years, materials in the sample examined are certainly more than 250 years old, a dating which may go back to the early 16th Century. The materials with Pb in sample 7 are three: in the priming [2PbCO3 – Pb(OH)2]; in the minium [Pb304]; in the upper gray layer and in the white layer, of lead white, cinnabar and carbon black.

 

B) Carbon Dating

The use of ‘Carbon Dating’ (or ‘Radio Carbon Dating’) procedures can be a valuable tool in the art world for the complicated purpose of dating paintings. This is a radiometric dating method using naturally occurring radioisotope carbon -14 (14c) to determine the age of carbonaceous and other organic material, as far back as about 60,000 years. Though carbon dating is not conclusive as a test taken by itself, it can confirm a spread of years before which a painting could not have been executed.

In general, carbon dating tests provide a window of years, which can be quite large. Other than the probability percentages of certain years within the window, there is no way to know the likelihood of each year. A recent example which demonstrates this exercise was undertaken among other tests on the vellum support for ‘La Bella Principessa’, a work subsequently authenticated by Martin Kemp and others, as being an autograph work by da Vinci. The result of that test gave “ … a 95.4% probability of a bracketed date of AD 1440 – 1650 …” Obviously this 210-year spread cannot establish a Leonardo attribution. However, the test does date the vellum support itself, just not the actual artwork on it.

Image of carbon dating results

Carbon Dating results obtained by ETH, Zurich

As previously described, the original handmade canvas of the ‘Earlier Mona Lisa’ has been relined on a much later machine-made canvas. The original painting and canvas cover the entire facing surface, but hardly any of the original canvas folds around the sides of the existing stretcher. However, a very small but acceptable sample of the original canvas was sacrificed and extracted for radio carbon dating from a zone located on one edge.

This test yielded a dating of the canvas between 1492 and 1652 (see graph), with a higher probability in the earlier part of that period. This date range is a standard and is one that is typically expected for dating results of paintings executed in the early 1500s. This test confirms that the canvas used in the ‘Earlier Mona Lisa’ can indeed be from the period during which Leonardo would have painted it, and fits with the chronology documented by Giorgio Vasari and the 1503 date confirmed by Agostino Vespucci.

Professor Hans-Arno Synal, of the Swiss Federal Institute of Technology, Zurich on reviewing the results of the test, states: “It is therefore clear that materials, which would have been originating at the turn of the 16th Century, would certainly give a similar radiocarbon age as the final result we have now achieved … ”