Pigments analysis
The chemical analysis of a micro element permits to identify the different pigments and binders which constitute the pictorial layer. Sometimes, it permits to date or authenticate easily a work of art.
The stratigraphic section
Executed in the same time than the pigments analysis, we can understand in a better way the painting structure with this method. Repainted, accidents or cracks are revealed and some pigments could be identified. It’s a precious tool for the restorer who works on a painting with great value.
We can see on the picture a red preparatory coat; this exact coat is given by analysis, covered with a yellowish preparatory coat which contains some particles of lead white, ivory-black and red ochre.
The final coat consists in the first example of lead white with a few quantity of vermilion and natural ultramarine. In the second example, we can see a crack which goes through all the layer, we notice a coat of ivory-black added to lead white and red iron oxide with a very thin grain.
These two examples are a characteristic of the technique of Dutch school of seventeenth century and consequently, we can situate this painting in a better way.
Scientific study of painting samples
Samples of paintings taken from Utrillo’s painting
The study of the layers has been done by microscope with a stratigraphic section, photography with normal light and photography under UV fluorescence.
The analysis of pigments and binders has been done by physical and micro chemical means under microscope.
Sample 1: Green painting
Layer description from the support
A: White preparation
- Calcium carbonate
- Proteins (glue)
- A few quantity of oil (probably coats above)
B: Green painting with a pigment which contains thin grain, varnish above, in other places the coat seems blue-green or simply blue due to a yellow pigment in more or less quantity.
- Artificial ultramarine
- Prussian blue
- Zinc yellow (zinc chromate)
- Yellow pigment with transparent iron oxide (Terre de Sienne)
- Charcoal black
- Zinc white
- Barium sulphate
- Oil
Echantillon I
Echantillon I sous fluorescence ulra-violette
Sample 2 : Red painting
Layer description from the support
Bright red coat with inclusions of white pigments, colorless mineral fragments and yellow pigments with thin grains. In another part of the sample, there is a purple painting which contains a red pigment and artificial ultramarine.
- Red Chromium
- Red lacquer
- Barium sulphate
- Zinc white
Echantillon II
Echantillon II sous fluorescence ulra-violette
Sample 3: 1 : Yellow-green painting
Description of the layer from the support
a: Bright red coat with inclusions of white pigments identical to 2
b: Dark blue-purple coat
- Red chromium
- Red lacquer
- Artificial ultramarine
- Barium sulphate
- Zinc white
- Oil
c: Yellow-green coat
- Prussian blue
- Carbon black
- Zinc yellow
- Barium sulphate
- Zinc white
- Calcium Carbonate
- Oil
Echantillon III/1
Echantillon III/1 sous fluorescence ulra-violette
Sample 3: 2 : Purple painting
Layer description from the support
a: Identical layers to II
b: Dark blue-purple painting with colorless mineral fragments, blue, red and yellow pigments which change gradually and get more greenish on the top of the layer because of a great quantity of yellow pigments.
- Prussian blue
- Artificial ultramarine
- Zinc yellow
- Barium sulphate
- Oil
Echantillon III/2
Echantillon III/2 sous fluorescence ulra-violette
Sample 4
Layer description from the support
a: Semitransparent layer with yellowish white with large particles of a dark pigment (or grime?)
- Calcium carbonate (chalk)
- Proteins (glue)
b: Thick white layer with pigments which contains thin blue and black grains. Large bits of colourless minerals.
- Zinc blue
- Artificial ultramarine
- Charcoal black
- Barium sulphate
- Oil
Echantillon IV
Echantillon IV sous fluorescence ulra-violette
Pigments and binders analysis
Micro photo sous lumière visible
From micro elements, physic and microchemist analysis of material allows identification of the several involved materials, pigments and binders which compose the pictorial layer. According to the case, this analysis can also be done by other means nondestructive, for example fluorescence X. This analysis takes part of the file of identification. The pigment or binder identification links the painting to a moment of an individual creation. These operations help us to situate the painting in time, the chemical elements and binders being in general characteristic of a period.
Sometimes, the falsification could be revealed by researching of anachronism. Presence of compatible pigments with the time of execution of a painting can comfort the work in a time period.
Echantillon IV sous fluorescence ulra-violette
Several methods are used, sometimes complementary. Among the most currently used in the field of painting, we can explain to you some examples:
Concerning pigment analysis, micro analysis with M.E.B (microscope electronic sweeping) with samples brings three informations. First, in the form of pictures in secondary electrons (E.S) that gives the topography of the sample.
Secondly, in the form of pictures of retro diffused electrons (E.R.D) that gives us a chemic “picture” of the sample. Finally we obtain an elementary analysis in energy dispersion of X rays (E.D.X) in the form of a specter. The objective is to identify the nature of pigments and loads, constituents of the sample painting taken on a work.
Then, X fluorescence is an elementary method of analysis. Without sampling and touching the painting, we can easily identify the chemical elements of the surface thanks to X rays.
Analyzed by spectroscopy Raman on elements taken from paintings, it’s a method of structural analysis that can identify materials of works. We use this analysis especially to differentiate titanium white “Anatase” of the titanium white “Rutile”, able to imply a variation of dating of approximately thirty years.
Finally, for material as binders, varnish, adhesives, we identified it with infrared spectrometry a “transformed of Fourier”, which, from the measurement of infrared intensity of light absorbed by material, it give its characteristics and its identification by comparison with materials of reference.