# The materiality of Neo-impressionism harmony: a non-invasive study of Paul Signac "Au temps d'Harmonie"

Emeline Pouyet, Laurence de Viguerie, Philippe Martinez, Philippe Walter

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Emeline Pouyet, Laurence de Viguerie, Philippe Martinez, Philippe Walter. The materiality of Neo-impressionism harmony: a non-invasive study of Paul Signac "Au temps d'Harmonie". Scientific Methods in Cultural Heritage Research Gordon Research Conference 2022, Jul 2022, Les Diablerets, Switzerland. . hal-04026848

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Submitted on 13 Mar 2023

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# The materiality of Neo-impressionism harmony: a non-invasive study of Paul Signac "Au temps d'Harmonie"

Emeline Pouyet ¹, Laurence de Viguerie ¹, Philippe Martinez ¹, Philippe Walter ¹

¹ Sorbonne Université, CNRS, Laboratoire d'Archéologie Moléculaire et Structurale (LAMS), Paris, France

The late nineteenth and early twentieth centuries were marked by tremendous innovations in art and science. On the one hand, with the rapid rise of the chemical industry, numerous new inorganic and organic pigments were developed and marketed as alternatives to well-established traditional pigments. On the other hand, development of spectrophotometry and the flourishing of numerous treatises on color theory, were soon made available to artists. Equipped with a new prismatic palette and new scientific theories, Neo-Impressionist artists extensively discussed and exploited color mixtures, and by using a variety of painting techniques, they created new facture. In this context, the *in-situ* analytical study of Paul Signac painting materials and techniques represents a unique opportunity to determine the relationships between nineteenth century literature on color theory and its application by the contemporaneous Neo-Impressionist painter.

## AN INTERDISCIPLINARY STUDY : ARCHIVAL INFORMATION, HISTORICAL COLOR THEORY & HISTORICAL PAINTINGS

### The Division : a definition from Paul Signac

d'Eugène Delacroix au Néo-impressionnisme, H. Floury, Libraire-Editeur, 1899

<figure><img src="image_4.png" /></figure>

"The Neo-Impressionist does not dot, he divides. Though, dividing is:

Ensuring all of the benefits from brightness, colouring, and harmony by means of:

1. The optical mixture of solely pure pigments (all the tints of the prism and all their tones);

2. The separation of the different elements (local color, color of the lighting, their interactions, etc.);

3. The equilibrium between these elements and their proportions (according to the laws of contrast, of gradation, and of irradiation);

4. The choice of a brushstroke is proportional to the dimensions of the painting."

### Research Objectives

through the development of a dedicated in-house analytical approach

In this context, scientific methods represent an unique opportunity to study Neo-Impressionist artworks to determine:

- the painting material choice made by Paul Signac

- the technique developed to apply and juxtapose the different paint layers as a function of color tint and hue, with regards to contemporaneous color theory

- the evolution of color/material system as a function of time

### Materials study: combination of in situ instrumentation

<figure><img src="image_5.png" /><figcaption>Specim VIS</figcaption></figure>

Equipped with a long working distance objective OLE140 400-1000nm Δλ=6nm V10E coupled with CCD (1600 × 1200 pixels)

<figure><img src="image_6.png" /><figcaption>Model Specim IQ</figcaption></figure>

400-1000nm
Δλ=7nm (204 bands)
Image: 512px x 512px

<caption>MicroScanX</caption>

Rh anode
Polycapillary optic
Beam size 150µm
70mm² SDD
Scan: 30 x 15 cm²

<figure><img src="image_7.png" /><figcaption>A series of seven oil on canvas and wood panel for « Au temps d'harmonie »</figcaption></figure>

Esquisse for Au temps d'Harmonie (les iris) n°254- 1893, Paul Signac, Oil on canvas, 26 x 35 cm², Private collection

<figure><img src="image_8.png" /></figure>

Studies for Au temps d'harmonie, Paul Signac, Oil on wood panel, Annonciade Museum and Private collection

<figure><img src="image_9.png" /></figure>

Au temps d'harmonie, Paul Signac, Oil on canvas (1893-1895) 410 × 310 cm², Montreuil City Hall

## CHEMICAL AND OPTICAL PROPERTIES OF "AU TEMPS D'HARMONIE" PAINTING AND RELATED STUDIES

<figure><img src="image_10.png" /><figcaption>### Drawing and Laws of contrast</figcaption></figure>

Drawings were observed for all preparatory studies, with mentions about color, i.e. in the above figure 'v. j.' for green/yellow, or 'mer' for sea. The main area of change of tint and hue are always present in the drawing, highlighting its importance for the gradation of the contrast at the painting scale.

<figure><img src="image_11.png" /><figcaption>### HSI Dataset</figcaption></figure>

The main challenge was to perform *in-situ* measurements for the final version of Au Temps d'Harmonie, exposed at 3 meters from the ground and facing a stair with no possibility to work close from the artwork. The long working distance Specim objective allowed acquiring HSI datasets further exploited for comparison with the various painted studies. Using this approach, pigments were identified as: vermilion, green (presumably copper arsenate type), cobalt blue, cobalt violet (arsenate), yellow (presumably chromate yellow), and pink colored anthraquinone dyes. The orange tints are obtained by mixing yellow and vermilion as previously identified in the studies.

<figure><img src="image_12.png" /><figcaption>### Paint brushstroke: a single pigment system ?</figcaption></figure>

Paul Signac uses a large variety of pigments for the preliminary studies and final painting. Mixtures of pigment are observed for the purple, pink, orange and green color dots, as such pure pigment paint systems were not solely use.

<caption>Chevreul chromatic circle (1st)</caption>

Des couleurs et de leurs applications aux arts industriels, Digeon (1855) - BnF

<figure><img src="image_13.png" /><figcaption>### Color space reference</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Au temps d'harmonie</figcaption></figure>

<figure><img src="image_15.png" /></figure>

Overall, this study allows the determination of Paul Signac palette and painting technique, from drawing to juxtaposition of painting dots. The specific study of Au Temps d'Harmonie painting and preliminary studies highlight a change of the use of materials by the artist from 1892 to 1895. The application of long working distance objective for HSI analyses of painted surface in isolated area showed great promises for further development. Finally the combined colorimetric study of contemporaneous colorimetric circles owned by the artist and the paintings confirmed the use of similar color space: approximately circular (in the a*,b* chromaticity diagram) and not centered.