The Canvas Support

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 arrival of 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 Ferronnière’ were painted on walnut panels that came from the same block of wood. The Louvre ‘Mona Lisa’ on the other hand, was painted on poplar, a wood more frequently used in Lombardy than Tuscany.

One cannot forget that Leonardo was not only a great inventor and innovator, but he was continually experimenting with new ideas and technology. Canvas was, by 1500, already in general 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. 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 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’, Professor 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 Perréal. It testifies to his spectacular exploration and development of novel media, tackling each commission as a fresh technical and aesthetic challenge…”

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’ – CAP CCCLIII.

Leonardo developed his technique of working on canvas as far back as his early apprenticeship in Verrocchio’s studio in the 1470s. One of the earliest serious references to Leonardo working on canvas was the great Giorgio Vasari, whose account relates: “ … and as he intended to be a painter by profession he carefully studied drawing from life. Sometimes he made clay models, draping the figures with rags dipped in plaster, and then drawing them painstakingly on fine Rheims cloth or prepared linen. These drawings were done in black and white with the point of a brush, and the results were marvelous … ” The earlier version of ‘Mona Lisa’, is on hand-woven canvas, a material with which Leonardo had significant experience before 1500, and is effectively similar to that which he had used for many of his early drapery studies.

 

Professor Frank Zöllner adds: “These carefully executed drawings served the artist both as studies and as a guide for the draperies in later paintings. Since they were in a sense models, these drawings were carried out with the greatest possible attention to detail in various techniques, often on durable linen, so that the next generation of young artists could learn from them.” This fine hand-woven linen canvas, known then as Rheims cloth, became a classic support used in his drapery studies, examples of which today are in the Louvre, the Uffizi in Florence, and the British Museum in London.

 

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. 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. They are plain tabby weaves with an average thread count of 18 threads per cm warp, and 16 threads per cm weft; and there is significant variation in the thickness. As with the ‘Mona Lisa’, these canvasses of course were also naturally hand-woven. Leonardo had had over 30 year’s experience working on canvas, dating from his apprenticeship days in Verrocchio’s studio, and therefore the fact that the ‘Earlier Version’ is on canvas would by no means not preclude it from being by Leonardo’s hand.

In 2005, a painting of a ‘Young Christ’, in oil on thin fabric, possibly linen, was presented by Professor Alessandro Vezzosi as an unpublished work by Salai. The connection to Isabella d’Este’s request, via Fra’ da Novellara, for a work “ … in that devout and sweet style … ” cannot be overlooked, and it may have been no coincidence that, in 1504, Salai was introduced to Isabella as a ‘worthy’ Leonardo pupil. This further dates the use of canvas in Leonardo’s studio to the purported execution period of the earlier version of ‘Mona Lisa’. Then, as recently as 2011, Professor Vezzosi enearthed another, altogether different painting, this time on the theme of Mona Lisa, that he believes could be by Salai. Given that it is on canvas, this lends further credence to the idea that this material would have been in use in Leonardo’s studio 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.
Another extremely important point relating to this portrait is that its very existence on canvas instead of a wood panel belies any suggestion that it could ever have been a ‘copy’ of the ‘Louvre Version’, or vice versa.

 

 

It can 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 other masterworks on canvas by Leonardo, including:

- ‘The Benois Madonna’, 1478 (St. Petersburg; see Wikipedia)

and some described as being on “ … canvas transferred from panel … ”, including:

- ‘The Madonna of the Rocks’ (a.k.a. ‘Virgin of the Rocks’), 1483-1486 (Paris)

- ‘Madonna Litta’, c. 1490 (St. Petersburg)

- ‘Bacchus’ [St.John the Baptist], 1510-1515 (Paris)

Hereunder are some notable early examples of works on canvas by other famous Renaissance artists of the same period:

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)

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 Leonardo’s earlier version of ‘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 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 Version’ 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 back of the ‘Earlier Version’ 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 (CaCO3), with some grains of quartz. With this colour as a base, the artist would be able 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 no shortage of evidence for this approach in 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. This portrait was executed c. 1490 in Milan, so availability of similar pigments as in Florence cannot be taken for granted. Another probe, on the subject’s dress, revealed that the pigment had to be of a ferruginous origin.

‘La Belle Ferronnière’, Leonardo’s ‘sister’ painting to ‘Lady with the Ermine’ also underwent laboratory testing at the Louvre in the early 1950s. Professor Pietro Marani, in his 2003 book: ‘Leonardo da Vinci – The Complete Paintings’ refers to Sylvie Béguin, 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.”

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 Ferronnière’, ‘The Musician’, and ‘St. Anne’.”

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’ that might have still existed. The process employed was Thermavision – an infrared 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 [Treatise ‘On Painting’]; 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 occurred at exactly the same period as the application of red ground on the earlier version of ‘Mona Lisa’. The two commissions likely coincided, so it is logical that the 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 addition, attention has been drawn to a recent analysis of pigments from Leonardo’s famous ‘Last Supper’. During restoration work on the fresco, Dr. Antoinette Gallone of the Milan Polytechnic found traces of calcite (calcium carbonate) in the preparatory layers. She found that the pigments in the analysis of this painting point clearly to it being a High Renaissance work.

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 argued that the reddish-brown ground on the earlier ‘Mona Lisa’ is compatible with some of Leonardo’s other significant paintings, and a possible sign 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 many of 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 calcium carbonate, lead white and bone black. Again, the colours specified above, by Leonardo in his Treatise, are in full use on this portrait. C. L. 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!”

L. Keith and A. 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 & 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

Prior to the examination by Lumiere Technology there have been two major examinations of the paint layers of Leonardo’s earlier ‘Mona Lisa’ in recent years: the first in 1977, by Dr. Hermann Kuhn, under the auspices of the Swiss Institute for Art Research, and a second in 2005 with the intensive diagnostic investigation by Dr. Maurizio Seracini. A total of nineteen probes were extracted, revealing results in both tests that were not only consistent with each other, but compatible with a paint palette Leonardo used on the ‘Louvre Version’, particularly the earlier layers.

In his Treatise ‘On Painting’, in the chapter ‘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 (this is the fine gesso known as ‘gesso sotile’*) and let it dry. Then draw your painting with tone (reddish-brown and purplish-grey layers) 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 (lead white), lacquer, and Flanders yellow (yellow ochre); the shadow will be made from black (bone 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.” (zinnober, Hgs – mercury sulphide)

“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 S. J. 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. He writes: “… the two major grounds in antiquity were chalk and gypsum, the former being the choice of northern European artists … the latter being preferred by the Italian and Spanish schools. Mixed with animal glue either were suitable coatings for panels (gypsum and glue being familiarly known as gesso), but for canvas preparation a different vehicle was the only sensible choice.” Here that author makes a separate distinction for canvas preparation; though Leonardo’s directions relate more to the original method.

The precise origin of the gypsum particles is not always easy to detect. “The absence of fibrous particles of Tuscan origin does not disprove the Tuscan origin (of a painting). The calcium component of the ground is usually a mixture of gypsum and andydrite in varying proportions, often occurring in particles that are fibrous … the samples found in Tuscan quarries show characteristics similar to those forming the grounds of many Tuscan paintings.”

Scientific Analysis Of The Pigments

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 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. Mauricio Seracini dated the results of his further 10 probes. The results hereunder 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. Also, it should be noted that in some cases different names given to the same pigments, perhaps according to each scientist’s education and experience. For example, Dr. Kuhn refers to calcium carbonate (CaCO3) throughout. Dr. Seracini’s report refers to this element as calcite. Calcite is a polymorph of calcium carbonate. He also refers to minium, a current name for a red oxide of lead.

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 calcium carbonate, and includes a few bigger grains of quartz. There is a subsequent grey layer of base consisting of calcium carbonate, lead white and bone black. This is covered by the flesh layers which contain lead white, calcium carbonate, a few grains of black vermilion, zinnober* (HgS – Mercury sulphide), vermilion, and yellow ochre. (*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, calcium carbonate, and red lacquer.

Probe #3: Mountain, yellow highlight pigment

Two tests were made on the yellowish to green- brown 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, calcium carbonate, 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 calcium carbonate, 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, calcium carbonate, lead white, green earth, and artificial copper blue called veriter.

Probe #8:Dress fold, yellow highlight pigment

Contained lead white, calcium carbonate, 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 calcium carbonate. 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.

Layers 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.

Layers 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.

Layers 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.

Layers 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.

Layers 7 +: Several layers of varnish.

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

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 and umber. 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 version of ‘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 Musées 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, (‘Mona Lisa – Inside the Painting’).

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 Version’. 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 Version’.

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 Louvre’s 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 Louvre publication also highlights an issue that until now has rarely been tackled: a comprehensive study of Leonardo’s work on canvas. In their 1992 book: ‘Studies in Conservation 37’, the authors E. Martin, N. Sonoda, and A. R. 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 might expect to gain a new understanding of his working techniques. Interestingly with this painting, there are really no surprises: as mentioned above in a slightly different context, Leonardo remains true to his 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, and which can indicate if the artwork was executed pre- or post-1750, after which date its composition changed. 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).

 

A Radioisotope is considered totally decayed when 12 t1/2 are passed. The data shown in the chart below indicate that all 210Pb isotopes present in the sample analysed are completely decayed. Since 210Pb has a t1/2-20.4 years, materials in the sample examined are certainly more than 250 years old, i.e. pre-1750, a dating which includes 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. However, important questions remain about its accuracy.
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 Professor 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.
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 (30 – 50mg) of the original canvas was sacrificed and extracted for radio carbon dating from a zone located on one edge. This sample of the canvas was then carbon tested by one of the world’s most reputable laboratories specializing in this field. The test results indicate a 95.4% probability of a date no later than 1455. This would align with an execution of the painting at the beginning of the 16th century and suggest that any later use as unlikely.