The artists’ materials of P. S. Krøyer: An analytical study of the artist’s paintings and tube colours by Raman, SEM–EDS and HPLC
© The Author(s) 2017
Received: 7 June 2017
Accepted: 18 August 2017
Published: 12 September 2017
Peder Severin Krøyer (1851–1909), known as P. S. Krøyer, is one of the most famous Danish painters, and a central figure in the Nordic artists’ colony established in Skagen at the end of the nineteenth century. Krøyer graduated in 1870 from the The Royal Danish Academy of Fine Arts, and early in his career he proved to have a unique talent as a portrait painter. His oeuvre counts numerous portrayals of scenes from local life and social gatherings, as well as commissioned portraits of prominent figures in the industry and the cultural life [1–3]. The commissioned works, along with his patronage and friendship with the tobacco manufacturer and art collector Heinrich Hirschsprung (1836–1908), secured Krøyer a considerable income and made him a prosperous painter [1, 2]. With Hirschsprung’s support Krøyer was able to make numerous study trips around Europe, which came to be of great influence on his career. In particular the grand tour of 4 years from 1877 to 1881 marked a turning point in his artistic style and working methods. During this tour Krøyer stayed for longer periods in Paris, where he attended classes at the atelier of the French artist Léon Bonnat (1833–1922) [3, 4]. After his return to Denmark Krøyer began to spend the summer months working in Skagen, a small fishing village in the northernmost part of Denmark that became a meeting point for Nordic artists during the 1880s . The Skagen painters, as they came to be known, found inspiration in the surrounding nature and local population in Skagen, and benefitted from the social and professional community among the artists. Their motives were most often painted “en plein air” with a clear influence from Naturalism and Realism. Today extensive collections of Krøyer’s paintings are exhibited at the Art Museums of Skagen, and at The Hirschsprung Collection in Copenhagen [1, 3]. The latter is also exhibiting Krøyer’s painting cabinet.
The two paintings, By the fireside. Portrait of Holger Drachmann with a red fez (hereinafter, Drachmann) and Christoffer mending nets in his living room (hereinafter, Christoffer), were painted by Krøyer in Skagen in 1903–1907 and 1886 respectively, and hence belong to the latter part of his oeuvre. Drachmann (Fig. 1, top) is one of many portrayals Krøyer did of his friend, the Danish writer and painter Holger Drachmann (1848–1908) . Krøyer’s friend and fellow Skagen-painter Michael Ancher (1849–1927) depicted Krøyer while working on the final stages of the painting (Fig. 1, bottom). It took Krøyer 4 years to complete the large portrait, which was unusual given the fact that Krøyer was known for his ability to work rapidly. At the time being though, he was struggling with mental illness, and was hospitalised several times . In contrast, the earlier portrait Christoffer from 1886 (Fig. 2, left) is an example of a rapidly executed painting, depicting a local fisherman working in a dark interior. The portrait clearly shows the influence of the realistic model painting and the concept “Valeur”, to which Krøyer was introduced during his stay at Léon Bonnat’s atelier. Krøyer gave the portrait as a gift to his friend, the French painter Ernest Baillet (1853–1902) as evidenced by the inscription in the upper left corner (Fig. 2, right). Both of the paintings are today a part of the collection at The Art Museums of Skagen.
Description of the paintings and tube colours
Pigments and fillers identified by SEM–EDS and Raman in the ground layer and paint layers of the two paintings; a: Drachmann, and b: Christoffer
(S2–S4), S5, S9–S13
S9?, S12, S13
S1–S5, S8, S9
S2, S3, S5
S1–S6, S8–S11, S13
S2, S3, S5
S2, S3, S5
(S2), S3–S7, S10, S11, S13
S5, S6, S8, S9
S3, S10, S13
List of trade names, durability, brands of the tube colours, and number of tubes
Cadmium yellow dark (Jaune de cadmium foncé) HH
Cadmium yellow light (Jaune de cadmium clair) HH
Brilliant yellow (Jaune brillant jaunâtre) HH
Cadmium lemon yellow (J. de cadmium citron) H
Chromium yellow light (Jaune de chrome clair)
Viridian (Vert émeraude) HH
Viridian (Vert émeraude)* HH
Chrome green light (Vert de chrome clair) HH
Chrome green medium (Vert de chrome moyen) HH
Cobalt blue (B. de cobalt vivace surfin) HH
Ivory black (Noir d’ivoire) HH
Snow white (Blanc de neige)* HH
Green lake light (Laque verte clair)
Madder lake golden rose (Laque garance rose doré)* H
Madder lake deep rose (Laque g. rose intense) HH
Madder lake rose (Laque de garance rose)
Felice Alman (Torino)
Carmine lake ordinary (Laque carminée ordinaire)
Lefranc et Cie (Paris)
Red oxide (oxide rouge) H/HH
Red oxide (oxide rouge)
Paint samples taken from the two paintings during conservation were made into cross sections by embedding in Technovit 2000 LC light curing resin placed in EasySections. The resin was cured for 10 min with blue light under a flow of nitrogen gas in a light-curing oven (Egger EL 1 plus N2). Finally the cross sections were polished wet with silicon carbide and then dry with Micro-Mesh (granularity 2400–12,000).
The samples and cross sections were studied with an optical microscope Axio Imager M1 (Carl Zeiss) under polarised white light and ultraviolet radiation with magnifications between 100 and 500× and the use of DeltaPix Insight.
MRS analyses were carried out with a Renishaw inVia dispersive micro-Raman spectrometer equipped with a 785 nm laser. The laser power was kept between 0.1 and 1 mW by neutral density filters to avoid thermal degradation. A detailed description can be found in ref .
SEM–EDS analyses were carried out on cross sections and paint samples placed on double sided conductive adhesive carbon tabs using a Hitachi S-3400 N scanning electron microscope with an energy dispersive X-ray spectrometer (SEM–EDS) operating at an acceleration voltage of 20 kV and low vacuum mode at 25 Pa. The EDS system, QUANTAX 200, was equipped with two 30 mm2 SDD X-ray detectors (XFlash® 6|30 Silicon Drift Detector) from Bruker instruments.
Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was used as supporting technique. ATR-FTIR spectra were recorded on a Perkin Elmer Spectrum One FTIR-spectrometer, fitted with a Universal ATR sampling accessory having a one-bounce composite zinc selenide and diamond crystal. Spectra of the samples were recorded over the range 4000–650 cm−1 with a resolution of 4 cm−1 and 4 accumulations.
HPLC analyses were carried out after mild HF extraction (2 M aqueous HF/dimethylformamide/acetonitrile = 2/1/1). The HPLC–DAD system used for the dye analyses was a Spetra-SYSTEM from ThermoScientific, controlled by ChromQuest 4software. A detailed description can be found in ref .
Results and discussion
The results from the pigment analysis carried out on samples taken from the two paintings are listed in Table 1. In the table a distinction is made between pigments found in the ground and paint layers, and the two paintings are noted with the letter a or b, designating the portrait of Drachmann and the portrait of Christoffer, respectively.
Dark blue grains of cobalt blue were likewise consistent in the samples taken from the two paintings. In one of the samples from of the portrait of Christoffer, cobalt blue was found in a mixture with minor amounts of synthetic ultramarine, the latter identified by Raman (Fig. 5e) . The sample was taken from the dark paint layers in the background (S10), and the ultramarine pigment was possibly applied as a substitute for black similar to the practice known from impressionist painters . Krøyer did not, however, avoid using regular black pigments, and carbon black was identified in both paintings by its characteristic broad Raman-bands (Fig. 5f) .
The vast majority of the tube colours were produced by the Danish colour merchant Vilhelm Pacht, whose colours, among others, were also used by Edvard Munch . In the late nineteenth and early twentieth century the tube colours from Vilhelm Pacht were mainly retailed by the large paint shop A. Stelling, established in central Copenhagen in 1860 . Besides from Pacht, Krøyer also bought tube colours from the competing Danish colour merchant Hermann Averhoff at the shop Kultorvets Farvehandel, where he also bought canvases (Fig. 4). Only two of the tube colours found in Krøyer’s painting cabinet were from foreign companies, these being respectively the French Lefranc et Cie and the Italian Felice Alman.
An investigation of price lists from Danish nineteenth century paint shops was carried out in the archives of the Royal Library of Denmark. Based on the archival information found on trade names and brands, it seems likely that the majority of the tube colours in Krøyer’s painting cabinet were bought in the last decade of the nineteenth century or later. The trade names on the tube colours were in most cases written on the label in both Danish and French. While some were rather simple and well-known names like “Cadmium yellow”, “Chromium yellow” and “Cobalt blue”, others like “Jaune Brilliant”, “Ivory black” and “Snow white” were more fanciful, but still common, examples of trade names used for artists’ colours in the nineteenth century [17–19]. Finally there were examples of trade names like “Green lake light”, “Red oxide”, and “Cadmium lemon yellow”, where the results showed no clear correlation between trade name and contents.
Pigments, fillers and dyes identified in the tube colours by Raman, SEM–EDS, and HPLC
Trade name (Brand)
Cadmium yellow dark (Pacht)
Cadmium yellow light (Pacht)
Brilliant yellow (Pacht)
CdS yellow, ZnO
Cadmium lemon yellow (Pacht)
Chromium yellow light (Pacht)
Cr2O3·2H2O, BaSO4, Si, carbon black
Chrome green light (Pacht)
Cr2O3·2H2O, CdS, ZnO, BaSO4
Chrome green medium (Pacht)
Cr2O3·2H2O, CdS, KZn2(CrO4)2(H3O2), ZnO, BaSO4
Cobalt blue (Pacht)
Ivory black (Pacht)
Snow white* (Pacht)
ZnO, carbon black
Green lake light (Averhoff)
Fe4[Fe(CN)6]3, BaSO4, Al
Naphthol yellow S, auramin O, martius yellow
Madder lake golden rose (Pacht)
CaCO3, Mg3Si4O10(OH)2, Al, P
Madder lake deep rose (Pacht)
CaCO3, BaSO4, Al, P
Madder lake rose (Alman)
Al, P, S, Sn
Carmine lake ordinary (Lefranc)
CaCO3, Al, Sn
Red oxide (Pacht)
CdS orange, Al
Red oxide (Averhoff)
Fe2O3, BaSO4, Al, P
Red oxide (Averhoff)
CdS orange, Al, P
In relation to the stability of chromate pigments the analysis of the two tube colours labelled “Chrome green light” and “Chrome green medium” should be noticed. The name “Chrome green” has typically been used for the mixture of chrome yellow and Prussian blue [20, 25], but in this case the tubes contained a mixture of viridian, zinc yellow, cadmium sulfide and barium sulfate. It seems very likely, that the manufacturer changed the composition of the colour in order to create an alternative to the traditional “Chrome green” based on more durable pigments. Similar examples have been reported by Townsend et al. . In general durability seems to have been an important matter to Danish colour merchants in the end of the nineteenth century. The tube colours from Vilhelm Pacht were ranked in the price lists (Table 2) as being either completely durable (HH), durable (H) or uncertain (without a letter).
Among the 32 tube colours in Krøyer’s painting cabinet, 6 tubes contained lake pigments indicated by their trade names. One tube labelled “Green lake light” showed a surprising result, whereas the remaining five tubes with trade names for various shades of red madder and carmine contained the expected dyes based on their names and the artists’ materials available in this period.
Four tube colours had trade names for variant shades of red madder i.e. “Madder lake golden rose”, “Madder lake deep rose”, and “Madder lake rose”. In the first mentioned HPLC-analysis identified the organic colourants to be purpurin and pseudopurpurin, which could be interpreted as Kopp’s purpurin  precipitated onto a substrate containing calcite and talc. Purpurin and alizarin were identified in the latter two, confirming a madder-based product best described as garancine [27, 28]. In the tube labelled “Carmine lake ordinary”, carminic acid was identified (Fig. 10c) showing that this lake was actually prepared from cochineal insect . Together with carminic acid, another unknown red dye compound was found, which perhaps indicates the extraction method of cochineal, but its significance is unclear.
Six tube colours, one from Vilhelm Pacht and five from Hermann Averhoff, were all labelled “Red oxide”. Despite having identical trade names and almost identical colours, the analysis showed a considerably variation in the contents of the tubes. Only one of the five tube colours from Averhoff was found to contain hematite as the main pigment as expected by the trade name (Fig. 9c). The remaining four all contained cadmium sulfide, and hence showed a discrepancy between trade name and contents. In addition all five tube colours contained red lakes based on the identification of typical mordants Al, P, and Sn [28, 30, 31]. The “Red oxide” from Pacht likewise contained a mixture of cadmium sulfide and a red lake identified by Raman as alizarin (Fig. 9d) and by HPLC as purpurin and alizarin (not shown).
The cases of the “Green lake light” and the “Red oxide” are just a few examples of the complexity that relates to artists’ colours from the 19th century . A clear correlation between trade name and contents is not always seen, and consequently artists have often not had a sound knowledge of the colours they used.
Relation between the analysed paintings and tube colours
Given the fact, that most of the tube colours in Krøyer’s painting cabinet were probably bought in the last decades of Krøyer’s life, it seemed reasonable to draw a line between the tube colours and the paintings from the latter part of Krøyer’s career. Especially the large portrait of Drachmann, finished only 2 years before Krøyer’s death in 1909, seemed to be closely linked to the tube colours found in the artist’s painting cabinet. Cadmium sulfide pigments, viridian, cobalt blue and zinc white were all examples of pigments found in both Krøyer’s portrait of Drachmann and in a number of his tube colours.
Zinc white appears to have been an important part of Krøyer’s palette in the latter part of his career [4, 32]. In the analysed samples from the Drachmann portrait, zinc white was present in all paint layers where it was applied in mixtures with a wide variety of other pigments. Moreover the colour “Snow white” containing zinc white pigment was the only white tube colour present in the painting cabinet. A part from the pure white tube colour, zinc white was only identified in one other tube colour, this being “Jaune brilliant” where it was mixed with cadmium sulfide. It thus looks as if Krøyer himself intentionally blended zinc white into his colours on the palette in order to lighten the variant shades, as zinc white was present in all areas of the portrait of Drachmann.
Some pigments like chromium yellow and cadmium chromate  were only found in the tube colours. It is uncertain to what extent Krøyer has actually used these pigments in his paintings. Further analyses of other paintings by the artist could possibly provide information with regard to this question. In contrast the pigments vermilion, minium and chromium orange were all identified in the Drachmann portrait, whereas they were not present in any of the tube colours in the painting cabinet. This emphasises that conclusions about an artist’s painting materials cannot be drawn based on access to the materials alone without including analyses of the paintings themselves.
The analyses carried out on the samples from the two paintings and the tube colours have given an insight in the painting materials used by Krøyer in the latter part of his career, e.g. the pigments applied on his palette, and his favourite brand in tube colours and colour merchants. In general Krøyer used the commercially produced artists’ materials that became available from colourmen during the nineteenth century. The canvases were bought ready grounded, either on the stretcher or by the metre, and the composition of the ground consisted of lead white, calcite and silicate. Krøyer’s palette consisted of both traditional pigments and modern ones developed in the eighteenth and nineteenth century, among these, several pigments containing chromium, cadmium and cobalt. In general the pigments found in Krøyer’s paintings and tube colours were expensive reflecting that Krøyer was a well-established and wealthy artist, who did not have to choose the cheaper alternatives. A noticeable change in Krøyer’s palette seems to have taken place somewhere in between 1886 and 1903, where lead white was replaced with zinc white.
The tube colours found in Krøyer’s painting cabinet were primarily from Danish colour merchants, with the majority from the colour manufacturer Vilhelm Pacht. Krøyer’s tube colours had trade names typical for artists’ paints used during that period of time. In most cases the pigment(s) found in the tubes matched what would be expected based on the trade name. However, notable exceptions were found, such as the rare cadmium chromate pigment present in the tube colour “Cadmium lemon yellow” , as well as the “Green lake light” and “Red oxides” described above. This illustrates that it was not always obvious to artists what they bought from their colour merchant. The fact that some pigments were found in the paintings, but not in any of the tube colours in the painting cabinet and vice versa, emphasises that conclusions about an artist’s painting materials cannot be drawn based on access to the materials alone without including analyses of the paintings themselves.
All authors contributed to data interpretation and to finalizing the manuscript. All authors read and approved the final manuscript.
The authors would like to thank The Art Museums of Skagen and The Hirschsprung Collection for kindly allowing investigation and sampling of Krøyer’s paintings and tube colours respectively. Furthermore, we wish to thank Cecile Glaude and Alexia Coudray from IRPA/KIK for assistance with the instrumental analyses, and curator Mette Bøgh Jensen from The Art Museums of Skagen for reviewing the art historical contents of the article. Finally, we thank Foundation Idella, Marie Månsson’s Foundation, and the School of Conservation Firenze grant, for making first authors research stay at IRPA/KIK in Brussels, Belgium possible.
The authors declare that they have no competing interests.
Ethics approval and consent to participate
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
- Hornung PM. Peder Severin krøyer. Copenhagen: Fogtdal; 2005.Google Scholar
- Saabye M. Krøyer: an international perspective. Copenhagen: The Hirschsprung Collection & Art Museums of Skagen; 2011.Google Scholar
- Scavenius B. Krøyer and the artists’ colony at skagen. Copenhagen: National Gallery of Ireland; 1999.Google Scholar
- Christiansen MB. The artists’ materials and painting technique of P. S. Krøyer. An investigation of the artist’s paintings and tube colours. (master’s thesis, in danish). Copenhagen: The Royal Danish Academy of Fine Arts, School of Conservation; 2016.Google Scholar
- Lauridsen CB, Sanyova J, Simonsen KP. Analytical study of modern paint layers on metal knight shields: the use and effect of titanium white. Spectrochim Acta Part A Mol Biomol Spectrosc. 2014;124:638–45.View ArticleGoogle Scholar
- Sanyova J. Mild extraction of dyes by hydrofluoric acid in routine analysis of historical paint micro-samples. Microchim Acta. 2008;162:361–70.View ArticleGoogle Scholar
- Rosekamp E. Krak—danmarks ældste forretninger som er grundlagt ml. 1100–1911. Valby: LFL’s Bladfond; 1950.Google Scholar
- Bell IM, Clark RJH, Gibbs PJ. Raman spectroscopic library of natural and synthetic pigments (pre -1850 ad). Spectrochim Acta Part A Mol Biomol Spectrosc. 1997;53:2159–79.View ArticleGoogle Scholar
- Burgio L, Clark RJH. Library of FT-raman spectra of pigments, minerals, pigment media and varnishes, and supplement to existing library of Raman spectra of pigments with visible excitation. Spectrochim Acta Part A Mol Biomol Spectrosc. 2001;57:1491–521.View ArticleGoogle Scholar
- Newman R. Chromium oxide greens. In: Fitzhugh EW, editor. Artists’ pigments. A handbook of their history and characteristics, vol. 3. Oxford: Oxford University Press; 1997. p. 273–93.Google Scholar
- Bomford D, Leighton J, Kirby J, Roy A. Art in the making: impressionism. London: National Gallery Publications Limited; 1990.Google Scholar
- Rogala D, Lake S, Maines C, Mecklenburg M. Condition problems related to zinc oxide underlayers: examination of selected abstract expressionist paintings from the collection of the Hirshhorn museum and sculpture garden, Smithsonian institution. J Amer Inst Conserv. 2010;49:96–113.View ArticleGoogle Scholar
- Faubel W, Simon R, Heissler S, Friedrich F, Weidler PG, Becker H, Schmidt W. Protrusions in a painting by Max Beckmann examined with confocal μ-XRF. J Anal At Spectrom. 2011;26:942–8.View ArticleGoogle Scholar
- Osmond G, Boon JJ, Puskar L, Drennan J. Metal stearate distributions in modern artists’ oil paints: surface and cross-sectional investigation of reference paint films using conventional and synchrotron infrared microspectroscopy. Appl Spectrosc. 2012;66:1136–44.View ArticleGoogle Scholar
- Hermans JJ, Keune K, van Loon A, Iedema PD. An infrared spectroscopic study of the nature of zinc carboxylates in oil paintings. J Anal At Spectrom. 2015;30:1600–8.View ArticleGoogle Scholar
- Kutzke H, Topalova-Casadiego B. Exploring an artist’s practice: Edvard Munch’s paint tubes. In: Eyb-Green S, Townsend JH, Clarke M, Nadolny J, Kroustallis S, editors. The artist’s process: technology and interpretation. London: Archetype Publications; 2012. p. 172–5.Google Scholar
- Fiedler I, Bayard MA. Cadmium yellows, oranges and reds. In: Feller RL, editor. Artists’ pigments. A handbook of their history and characteristics, vol. 1. London: Archetype Publications; 1986. p. 65–108.Google Scholar
- Winter J, Fitzhugh EWF. Pigments based on carbon. In: Berrie BH, editor. Artists’ pigments. A handbook of their history and characteristics, vol. 4. London: Archetype Publications; 2007. p. 1–37.Google Scholar
- Kühn H. Zinc white. In: Feller RL, editor. Artists’ pigments. A handbook of their history and characteristics, vol. 1. London: Archetype Publications; 1986. p. 169–86.Google Scholar
- Kühn H, Curran M. Chrome yellow and other chromate pigments. In: Feller RL, editor. Artists’ pigments. A handbook of their history and characteristics, vol. 1. London: Archetype Publications; 1986. p. 187–217.Google Scholar
- Christiansen MB, Sørensen MA, Sanyova J, Bendix J, Simonsen KP. Characterisation of the rare cadmium chromate pigment in a 19th century tube colour by Raman, FTIR, X-ray and EPR. Spectrochim Acta Part A Mol Biomol Spectrosc. 2017;175:208–14.View ArticleGoogle Scholar
- Casadio F, Xie S, Rukes SC, Myers B, Gray KA, Warta R, Fiedler I. Electron energy loss spectroscopy elucidates the elusive darkening of zinc potassium chromate in Georges Seurat’s A Sunday on La Grande Jatte-1884. Anal Bioanal Chem. 2011;399:2909–20.View ArticleGoogle Scholar
- Zanella L, Casadio F, Gray KA, Warta R, Ma Q, Gaillard J-F. The darkening of zinc yellow: xanes speciation of chromium in artist’s paints after light and chemical exposures. J Anal At Spectrom. 2011;26:1090–7.View ArticleGoogle Scholar
- Monico L, Van der Snickt G, Janssens K, De Nolf W, Miliani C, Dik J, Radepont M, Hendriks E, Geldof M, Cotte M. Degradation process of lead chromate in paintings by Vincent van Gogh studied by means of synchrotron X-ray spectromicroscopy and related methods. 2. Original paint layer samples. Anal Chem. 2011;83:1224–31.View ArticleGoogle Scholar
- Berrie BH. Prussian blue. In: FitzHugh EW, editor. Artists’ pigments. A handbook of their history and characteristics, vol. 3. London: Archetype Publications; 1997. p. 191–217.Google Scholar
- Townsend JH, Carlyle L, Khandekar N, Woodcock S. Later nineteenth century pigments: evidence for additions and substitutions. Conservator. 1995;19:65–78.View ArticleGoogle Scholar
- Degano I, Tognotti P, Kunzelman D, Modugno F. HPLC–DAD and HPLC–ESI–Q–TOF characterisation of early 20th century lake and organic pigments from Lefranc archives. Herit Sci. 2017;5:7.View ArticleGoogle Scholar
- Schweppe H, Winter J. Madder and alizarin. In: Fitzhugh EWF, editor. Artists’ pigment. A handbook of their history and characteristics, vol. 3. New York: Oxford University Press; 1997. p. 109–42.Google Scholar
- Schweppe H, Roosen-Runge H. Carmine—cochineal carmine and kermes carmine. In: Fellor RL, editor. Artists’ pigments. A handbook of their history and characteristics, vol. 1. London: Archetype Publications; 1986. p. 255–83.Google Scholar
- Kirby J, Spring M, Higgitt C. The technology of red lake pigment manufacture: study of the dyestuff substrate. Natl Gallery Tech Bull. 2005;26:71–87.Google Scholar
- Saunders D, Kirby J. Light-induced colour changes in red and yellow lake pigments. Natl Gallery Tech Bull. 1994;15:79–97.Google Scholar
- Andersen CK, Taube M, Vila A, Baadsgaard E. Zinc, paint loss and harmony in blue: degradation problems in Peder Severin Krøyer’s paintings and the possible role of zinc white. Perspective. 2016:1–16.Google Scholar