Tof-SIMS spectra of historical inorganic pigments: Calcium white pigments in both polarities

Bouvier, Caroline; Van Nuffel, Sebastiaan; Brunelle, Alain

doi:10.1116/6.0003592

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is increasingly used to analyze cultural heritage materials because it can simultaneously detect organic and inorganic materials while mapping them on a surface. The precise identification of a pigment in a specific layer of a painting or of remaining color on a statue can inform about the technique used or the time of manufacture as well as expose possible forgeries when anachronistic ingredients are identified. Reference spectra are required to confidently identify a given pigment using ToF-SIMS. This database focuses on six white pigments made from calcium-rich natural or synthetized materials, prepared following traditional processes. Such pigments are frequently found in the preparation layers, namely, “ground,” separating the support from the observable paint layers, and providing a smooth surface to hold the paint on while preventing its absorption by the substrate. Differentiating between these pigments is helpful to better describe the painting practice. Here, ToF-SIMS reference spectra using a Bi₃⁺ primary ion species are presented for both polarities.

Accession #: 01931, 01932, 01933, 01934, 01935, 01936
Technique: SIMS
Specimen: Alba Albula, Bianco San Giovanni, Eggshell white, Dolomite, Anhydrite plaster, Natural alabaster
Instrument: IONTOF, TOF SIMS IV
Major Species in Spectra: O, H, Si, S, Al, C, Ca, Na, Mg, K, P, Cl
Minor Species in Spectra: Hydrocarbon contamination
Published Spectra: 12
Spectral Category: Reference

INTRODUCTION

ToF-SIMS imaging can detect a wide range of elements, so colored minerals can be identified and mapped, given that reference spectra are available for reliable assignment. Here, we provide a ToF-SIMS spectral database for six white pigments made of calcium-rich materials. Such materials are likely to be present in historical paintings and painted objects, especially in the deeper layers, commonly referred to as “ground” or “preparation” layers. Their structure and composition depends on the time and place in art history.

The reference materials were supplied by specialized manufacturers selling pigments reproducing historical recipes as closely as possible, such as Kremer Pigmente GmbH, Masters Pigments, Laverdure, and Sennelier. Pigments were available as finely ground powder of variable particle size (between one and a few tens of μm) conditioned in glass sealed vials. In paintings, pigment particles are dispersed and not dissolved, so all references were analyzed without any preparation treatment. Natural and synthetic pigments may contain impurities, and specimen compositions described below are the major components as found on the material data sheets provided by the suppliers.

A stainless-steel spatula was cleaned with propan-2-ol and the powder was directly deposited on a 1 × 1 mm² piece of conductive double-sided tape (3M Electrically Conductive Adhesive Transfer Tape 9703) already fixed to a 1 cm × 1 cm × 0.125 mm stainless steel plate (17-7PH, Goodfellow Cambridge Limited, UK) fitting the dimensions of the sample holder. A hand press covered with clean aluminum foil was applied onto the powder to fix it to the tape. This allowed us to minimize the risk of dust formation when operating in the analysis chamber under ultrahigh vacuum (10⁻⁸–10⁻⁹ hPa) while ensuring a flat surface.

All spectra were obtained on an IONTOF TOF SIMS IV equipped with a 25 keV bismuth liquid metal ion gun and an argon gas cluster ion beam (GCIB). Before all analyses, a 500 × 500 μm² surface was cleaned using 1500–2000 Ar clusters with a kinetic energy of 20 keV (sputter ion dose 2 × 10¹⁵ ions/cm²). Analyses were then performed on a 250 × 250 μm² area centered in this larger cleaned area, rastered over 128 × 128 pixels using the high current bunched mode. Primary ion dose (25 keV Bi₃⁺) was 4.35 × 10¹¹ ions/cm². Surface potential was compensated and charging of the sample was compensated with the low-energetic 20 eV electrons of the flood gun.

All positive polarity data were calibrated using the same set of peaks appearing in all spectra, namely, Na⁺ at m/z 22.99, Ca⁺ at m/z 39.96, Ca₂O⁺ at m/z 95.92, Ca₃O₂⁺ at m/z 151.88, Ca₄O₃⁺ at m/z 207.83, Ca₅O₄⁺ at m/z 263.79, and Ca₆O₅⁺ at m/z 319.75. All negative polarity data were calibrated using combinations of the following ions: Cl⁻ at m/z 34.97, CaO⁻ at m/z 55.96, CaO₂H⁻ at m/z 72.96, Ca₂O₃H⁻ at m/z 128.92, and Ca₃O₄H⁻ at m/z 184.88. These calibration lists allowed for an adequate coverage of the mass range of interest, and the calcium containing calibration ions could be verified using their isotopic pattern. The actual calibration set for each individual dataset can be found in the associated table.

Figures and tables presented below contain the major peaks for both polarities. Each pigment is uniquely identified thanks to an accession number and they are grouped according to their composition and described in the following section. Their historical relevance is briefly described based on the current literature.^1–5 The Spectrum ID# refers to that number, added with “−01” for positive spectra and with “−02” for negative spectra.

SPECIMEN DESCRIPTION (ACCESSION # 01931)

Specimen: Alba Albula, warm white chalk from Albula, Switzerland (Kremer Pigmente ref. 11283)

CAS Registry #: 471-34-1

Specimen Characteristics: Unknown homogeneity; solid; unknown crystallinity; dielectric; inorganic compound; powder

Chemical Name: Calcium carbonate

Source: Kremer Pigmente GmbH

Specimen Composition: CaCO₃

Form: Ground pigment powder

History and Significance: White earths derived directly from calcite-rich clay sediments are one of the oldest pigments. They are often found in the preparation layer applied to the substrate of a painting. This white pigment with a beige hue is made by ground stones naturally found in the Albula mountain pass (Switzerland). It is likely to contain other minerals than calcite.

As Received Condition: Ground pigment powders were stored in a sealed glass vial in a wooden box, protected from daylight. Stored at room temperature.

Analyzed Region: Areas of 250 × 250 μm²

Ex Situ Preparation/Mounting: Powder was deposited and pressed onto conductive double-sided tape attached to stainless steel 1 × 1 cm² plates. The resulting deposit of powder had a flat surface and was fixed in a suitable way for the vacuum chamber. The plate was directly mounted on a “backmount” sample holder (IONTOF).

In Situ Preparation: None

Charge Control Conditions and Procedures: A low energy electron flood gun was used. Bias voltage between 20 and −30 V. Flood gun filament current 2.35A. Residual surface potential was compensated before analysis.

Temp. During Analysis: 300 K

Pressure During Analysis: Between 1 × 10⁻⁵ and 1 × 10⁻⁶ Pa

Pre-analysis Beam Exposure: Ar_1500−2000, 20 keV, 2 × 10¹⁵ ions/cm²

SPECIMEN DESCRIPTION (ACCESSION # 01932)

Specimen: Bianco San Giovanni (Kremer Pigmente ref. 11415)

CAS Registry #: 471-34-1 and 1305-62-0-1

Specimen Characteristics: Unknown homogeneity; solid; unknown crystallinity; dielectric; inorganic compound; powder

Chemical Name: Calcium carbonate with calcium hydroxide

Source: Kremer Pigmente GmbH

Specimen Composition: CaCO₃ + Ca(OH)₂

Form: Ground pigment powder

History and Significance: White pigment prepared according to Cennino Cenninis recipe. Mainly composed of hydrated lime that was slowly dried and very finely ground (well below 150 μm for instance).

As Received Condition: Ground pigment powders were stored in a sealed glass vial in a wooden box, protected from daylight. Stored at room temperature.

Analyzed Region: Areas of 250 × 250 μm²

Ex Situ Preparation/Mounting: Powder was deposited and pressed onto conductive double-sided tape attached to stainless steel 1 × 1 cm² plates. The resulting deposit of powder had a flat surface and was fixed in a suitable way for the vacuum chamber. The plate was directly mounted on a “backmount” sample holder (IONTOF).

In Situ Preparation: None

Charge Control Conditions and Procedures: A low energy electron flood gun was used. Bias voltage between 20 and −30 V. Flood gun filament current 2.35 A. Residual surface potential was compensated before analysis.

Temp. During Analysis: 300 K

Pressure During Analysis: Between 1 × 10⁻⁵ and 1 × 10⁻⁶ Pa

Pre-analysis Beam Exposure: Ar_1500−2000, 20 keV, 2 × 10¹⁵ ions/cm²

SPECIMEN DESCRIPTION (ACCESSION # 01933)

Specimen: Eggshell White (Kremer Pigmente ref. 11410)

CAS Registry #: Unknown

Specimen Characteristics: Unknown homogeneity; solid; unknown crystallinity; dielectric; inorganic compound; powder

Chemical Name: Ground eggshell

Source: Kremer Pigmente GmbH

Specimen Composition: CaCO₃, MgCO₃, Ca₃(PO₄)₂, proteins from the shell

Form: Ground pigment powder

History and Significance: Finely ground eggshell is an easily accessible source of white pigment in a workshop and is frequently mentioned in preparations. The material has been classified as an inorganic pigment in this paper, as it mainly consists of calcium and magnesium carbonates. It is, however, worth noticing that some fragments originating from the peptide backbone of proteins, naturally found in the eggshell structure, can be detected using ToF-SIMS in this pigment.

As Received Condition: Ground pigment powders were stored in a sealed glass vial in a wooden box, protected from daylight. Stored at room temperature.

Analyzed Region: Areas of 250 × 250 μm²

Ex Situ Preparation/Mounting: Powder was deposited and pressed onto conductive double-sided tape attached to stainless steel 1 × 1 cm² plates. The resulting deposit of powder had a flat surface and was fixed in a suitable way for the vacuum chamber. The plate was directly mounted on a “backmount” sample holder (IONTOF).

In Situ Preparation: None

Charge Control Conditions and Procedures: A low energy electron flood gun was used. Bias voltage between 20 and −30 V. Flood gun filament current 2.35 A. Residual surface potential was compensated before analysis.

Temp. During Analysis: 300 K

Pressure During Analysis: Between 1 × 10⁻⁵ and 1 × 10⁻⁶ Pa

Pre-analysis Beam Exposure: Ar_1500−2000, 20 keV, 2 × 10¹⁵ ions/cm²

SPECIMEN DESCRIPTION (ACCESSION # 01934)

Specimen: Dolomite 10 μ (Kremer Pigmente ref. 58740)

CAS Registry #: 16389-88-1

Specimen Characteristics: Unknown homogeneity; solid; unknown crystallinity; dielectric; inorganic compound; powder

Chemical Name: Natural calcium-magnesium carbonate

Source: Kremer Pigmente GmbH

Specimen Composition: CaMg(CO₃)₂

Form: Ground pigment powder

History and Significance: White CaMg(CO₃)₂-rich white sediments or minerals are often found in the preparation layer applied to the substrate of a painting.

As Received Condition: Ground pigment powders were stored in a sealed glass vial in a wooden box, protected from daylight. Stored at room temperature.

Analyzed Region: Areas of 250 × 250 μm²

Ex Situ Preparation/Mounting: Powder was deposited and pressed onto conductive double-sided tape attached to stainless steel 1 × 1 cm² plates. The resulting deposit of powder had a flat surface and was fixed in a suitable way for the vacuum chamber. The plate was directly mounted on a “backmount” sample holder (IONTOF).

In Situ Preparation: None

Charge Control Conditions and Procedures: A low energy electron flood gun was used. Bias voltage between 20 and −30 V. Flood gun filament current 2.35 A. Residual surface potential was compensated before analysis.

Temp. During Analysis: 300 K

Pressure During Analysis: Between 1 × 10⁻⁵ and 1 × 10⁻⁶ Pa

Pre-analysis Beam Exposure: Ar_1500−2000, 20 keV, 2 × 10¹⁵ ions/cm²

SPECIMEN DESCRIPTION (ACCESSION # 01935, 01936)

Specimen: (Accession #01935) Anhydrite plaster, burnt gypsum (Kremer Pigmente ref. 58320), (Accession #01936) Natural alabaster plaster (Kremer Pigmente ref. 58340).

CAS Registry #: 7778-18-9

Specimen Characteristics: Unknown homogeneity; solid; unknown crystallinity; dielectric; inorganic compound; powder

Chemical Name: (Accession #01935) Calcium sulfate anhydrite, (Accession #01936) Calcium sulfate dihydrate + calcium sulfate alpha hemihydrate

Source: Kremer Pigmente GmbH

Specimen Composition: (Accession #01935) CaSO₄, (Accession #01936) CaSO₄⋅1/2H₂O (n = 1/2, 2)

Form: Ground pigment powder

History and Significance: Natural plasters are found in many paint mixtures as a filler to lighten a color or as a preparation material. Characterizing gypsum is important to understand the structure of a painted artwork. Natural gypsum contains strontium inclusions.

As Received Condition: Ground pigment powders were stored in a sealed glass vial in a wooden box, protected from daylight. Stored at room temperature.

Analyzed Region: Areas of 250 × 250 μm²

Ex Situ Preparation/Mounting: Powder was deposited and pressed onto conductive double-sided tape attached to stainless steel 1 × 1 cm² plates. The resulting deposit of powder had a flat surface and was fixed in a suitable way for the vacuum chamber. The plate was directly mounted on a “backmount” sample holder (IONTOF).

In Situ Preparation: None

Charge Control Conditions and Procedures: A low energy electron flood gun was used. Bias voltage between 20 and −30 V. Flood gun filament current 2.35 A. Surface potential was corrected (sample dependent).

Temp. During Analysis: 300 K

Pressure During Analysis: Between 1 × 10⁻⁵ and 1 × 10⁻⁶ Pa

Pre-analysis Beam Exposure: Ar_1500−2000, 20 keV, 2 × 10¹⁵ ions/cm²

INSTRUMENT CONFIGURATION

Manufacturer and Model: IONTOF, TOF SIMS IV

Analyzer Type: Time-of-flight

Sample Rotation: No

Rotation Rate: 0 rpm

Oxygen Flood Source: None

Oxygen Flood Pressure: N/A

Other Flood Source: None

Other Flood Pressure: N/A

Unique Instrument Features Used: None

Energy Acceptance Window: 20 eV

Post-acceleration Voltage: 10 000 eV

Sample Bias: 10–20 eV

Specimen Normal-to-Analyzer $(Θ e)$ : 0°

■ Ion sources

Ion source 1 of 2

Purpose of this Ion Source: Analysis beam

Ion Source Manufacturer: IONTOF GmbH

Ion Source Model: Liquid Metal Ion Gun (LMIG) with bismuth cluster (25 keV)

Beam Mass Filter: Yes

Beam Species and Charge State: Bi₃⁺

Beam Gating Used: Double pulsed + Bunched

Additional Beam Comments: None

Beam Voltage: 25 000 eV

Net Beam Voltage (impact voltage): 25 000 eV

Ion Pulse Width: 0.8–1.2 ns

Ion Pulse Rate: 5–10 kHz

DC Beam Current: ∼10 nA

Pulsed Beam Current: ∼0.0004 nA

Current Measurement Method: Faraday cup

Beam Diameter: ∼2 μm

Beam Raster Size: 250 × 250 μm²

Raster Pixel Dimensions: 128 × 128

Beam Incident Angle: 45°

Source-to-Analyzer Angle: 45°

Ion source 2 of 2

Purpose of this Ion Source: Sputtering beam

Ion Source Manufacturer: IONTOF GmbH

Ion Source Model: GCIB

Beam Mass Filter: Yes

Beam Species and Charge State: Ar_n⁺ with n = 1500−2000

Beam Gating Used: Wien filter

Additional Beam Comments: Used as sputter gun, not analysis mode

Beam Voltage: 20 000 eV

Net Beam Voltage (impact voltage): 20 000 eV

Ion Pulse Width: N/A ns

Ion Pulse Rate: N/A

DC Beam Current: ∼10 nA

Pulsed Beam Current: N/A

Current Measurement Method: Faraday cup

Beam Diameter: ∼50 μm

Beam Raster Size: 500 × 500 μm²

Raster Pixel Dimensions: N/A

Beam Incident Angle: 45°

Source-to-Analyzer Angle: 45°

SPECTRAL FEATURES TABLE

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01931-01	23.984 (−42.8)	Mg⁺	–
	26.980 (−30.0)	Al⁺	Clay
	27.975 (−33.7)	Si⁺	Clay
	38.965 (52.6)	K⁺	–
	79.945 (38.0)	CaMgO⁺	–
	135.900 (3.30)	Ca₂MgO₂⁺	–
	191.858 (4.51)	Ca₃O₂MgO⁺	–
	231.833 (−17.0)	Ca₃O₂(MgO)₂⁺	–
	247.816 (5.49)	Ca₄O₃MgO⁺	–
	287.796 (5.88)	Ca₄O₃(MgO)₂⁺	CaCO₃
	303.773 (3.81)	Ca₅O₄MgO⁺	CaCO₃

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01931-01	23.984 (−42.8)	Mg⁺	–
	26.980 (−30.0)	Al⁺	Clay
	27.975 (−33.7)	Si⁺	Clay
	38.965 (52.6)	K⁺	–
	79.945 (38.0)	CaMgO⁺	–
	135.900 (3.30)	Ca₂MgO₂⁺	–
	191.858 (4.51)	Ca₃O₂MgO⁺	–
	231.833 (−17.0)	Ca₃O₂(MgO)₂⁺	–
	247.816 (5.49)	Ca₄O₃MgO⁺	–
	287.796 (5.88)	Ca₄O₃(MgO)₂⁺	CaCO₃
	303.773 (3.81)	Ca₅O₄MgO⁺	CaCO₃

Accession #:	01931-01
■ Specimen:	Alba Albula – Kremer Pigmente ref. 11283 – Positive polarity
■ Technique:	SIMS
Instrument:	IONTOF, TOF SIMS IV
Analyzer Type:	Time-of-flight
Analyzer Mass Resolving Power:	2500 m/Δm
Mass Resolving Power Determined at:	27 Da
Species Used for Mass Calibration:	Na⁺, Ca⁺, CaO⁺, Ca₂O⁺, Ca₃O₂⁺, Ca₄O₃⁺, Ca₅O₄⁺, Ca₆O₅⁺
Specimen Normal-to-Analyzer:	0°
Source-to-Analyzer Angle:	45°
Primary Beam Ion Gun:	LMIG
Primary Ion Species:	Bi₃⁺
Primary Ion Dose:	4.34 × 10¹¹ ion/cm²
Primary Ion Pulse Width:	0.8–1.2 ns
Primary Ion Pulse Rate:	5 kHz
Net Beam Voltage:	25 000 eV
Pulsed Beam Current:	0.000 21 nA
DC Beam Current:	14.6 nA
Beam Diameter:	∼2 μm
Beam Raster Size:	250 × 250 μm²
Beam Incident Angle:	45°
Secondary Source Polarity:	Positive
Mass Range Minimum:	0 Da
Mass Range Maximum:	3545 Da
Spectrum Dead Time Corrected:	Yes
Total Spectral Acquisition Time:	210 s

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01931-02	15.995 (−8.90)	O⁻	–
	63.961 (−16.7)	SO₂⁻	–
	75.966 (43.5)	SiO₃⁻	Clay
	79.959 (16.3)	SO₃⁻	–
	99.946 (−14.8)	CaCO₃⁻	CaCO₃
	116.948 (−17.9)	CaOHCO3⁻	CaCO₃
	118.938 (−1.81)	AlSiO₄⁻	Clay
	178.907 (6.51)	Si₂AlO₆⁻	Clay

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01932-01	39.962 (4.34)	Ca⁺	Ca(OH)₂
	56.965 (3.08)	CaOH⁺	Ca(OH)₂
	95.920 (6.66)	Ca₂O⁺	Ca(OH)₂
	111.916 (16.7)	Ca₂O₂⁺	Ca(OH)₂
	112.925 (24.1)	Ca₂O₂H⁺	Ca(OH)₂
	151.878 (3.21)	Ca₃O₂⁺	Ca(OH)₂
	167.873 (4.08)	Ca₃O₃⁺	Ca(OH)₂
	168.881 (6.44)	Ca₃O₃H⁺	Ca(OH)₂
	207.833 (−6.07)	Ca₄O₃⁺	Ca(OH)₂
	223.829 (−1.46)	Ca₄O₄⁺	Ca(OH)₂
	224.838 (1.07)	Ca₄O₄H⁺	Ca(OH)₂
	263.789 (−10.4)	Ca₅O₄⁺	Ca(OH)₂
	279.784 (−10.1)	Ca₅O₅⁺	Ca(OH)₂
	280.794 (−2.46)	Ca₅O₅H⁺	Ca(OH)₂
	319.744 (−18.9)	Ca₆O₅⁺	Ca(OH)₂

Accession #:	01932-01
■ Specimen:	Bianco San Giovanni – Kremer Pigmente ref. 11415 – Positive polarity
■ Technique:	SIMS
Instrument:	IONTOF, TOF SIMS IV
Analyzer Type:	Time-of-flight
Analyzer Mass Resolving Power:	2900 m/Δm
Mass Resolving Power Determined at:	27 Da
Species Used for Mass Calibration:	Na⁺, Ca⁺, CaO⁺, Ca₂O⁺, Ca₃O₂⁺, Ca₄O₃⁺, Ca₅O₄⁺, Ca₆O₅⁺
Specimen Normal-to-Analyzer:	0°
Source-to-Analyzer Angle:	45°
Primary Beam Ion Gun:	LMIG
Primary Ion Species:	Bi₃⁺
Primary Ion Dose:	4.37 × 10¹¹ ion/cm²
Primary Ion Pulse Width:	0.8–1.2 ns
Primary Ion Pulse Rate:	5 kHz
Net Beam Voltage:	25 000 eV
Pulsed Beam Current:	0.000 16 nA
DC Beam Current:	15.7 nA
Beam Diameter:	∼2 μm
Beam Raster Size:	250 × 250 μm²
Beam Incident Angle:	45°
Secondary Source Polarity:	Positive
Mass Range Minimum:	0 Da
Mass Range Maximum:	3545 Da
Spectrum Dead Time Corrected:	Yes
Total Spectral Acquisition Time:	250 s

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01932-02	44.999 (8.89)	CO₂H⁻	CaCO₃
	56.966 (3.55)	CaOH⁻	CaCO₃/Ca(OH)₂
	59.986 (17.2)	CO₃⁻	CaCO₃
	72.964 (40.0)	(CaO)OH⁻	Ca(OH)₂
	89.965 (13.5)	(CaO)(OH)₂⁻	Ca(OH)₂
	90.974 (23.7)	(CaOH)(OH)₂⁻	Ca(OH)₂
	99.949 (6.77)	CaCO₃⁻	CaCO₃/Ca(OH)₂
	115.940 (−27.8)	(CaO)CO₃⁻	CaCO₃/Ca(OH)₂
	116.951 (−1.12)	(CaOH)CO₃⁻	CaCO₃/Ca(OH)₂
	128.921 (17.1)	(CaO)₂(OH)⁻	Ca(OH)₂
	136.928 (30.0)	Ca₂H(CO)₂⁻	CaCO₃/Ca(OH)₂
	146.929 (2.06)	H(CaO)₂(OH)₂⁻	Ca(OH)₂
	152.921 (16.3)	Ca₂OH(CO)₂⁻	CaCO₃/Ca(OH)₂
	168.888 (43.6)	Ca₃O₃H⁻	Ca(OH)₂
	172.911 (15.0)	(CaO)₂CO₃H⁻	CaCO₃/Ca(OH)₂
	184.878 (11.3)	(CaO)₃(OH)⁻	Ca(OH)₂
	202.885 (−4.64)	H(CaO)₃(OH)₂⁻	Ca(OH)₂
	240.832 (−6.09)	(CaO)₄(OH)⁻	Ca(OH)₂

Accession #:	01932-02
■ Specimen:	Bianco San Giovanni – Kremer Pigmente ref. 11415 – Negative polarity
■ Technique:	SIMS
Instrument:	IONTOF, TOF SIMS IV
Analyzer Type:	Time-of-flight
Analyzer Mass Resolving Power:	2500 m/Δm
Mass Resolving Power Determined at:	25 Da
Species Used for Mass Calibration:	Cl⁻, CaO⁻, Ca₂O₃H⁻, Ca₃O₄H⁻
Specimen Normal-to-Analyzer:	0°
Source-to-Analyzer Angle:	45°
Primary Beam Ion Gun:	LMIG
Primary Ion Species:	Bi₃⁺
Primary Ion Dose:	4.37 × 10¹¹ ion/cm²
Primary Ion Pulse Width:	0.8–1.2 ns
Primary Ion Pulse Rate:	5 kHz
Net Beam Voltage:	25 000 eV
Pulsed Beam Current:	0.000 16 nA
DC Beam Current:	15.7 nA
Beam Diameter:	∼2 μm
Beam Raster Size:	250 × 250 μm²
Beam Incident Angle:	45°
Secondary Source Polarity:	Negative
Mass Range Minimum:	0 Da
Mass Range Maximum:	3545 Da
Spectrum Dead Time Corrected:	Yes
Total Spectral Acquisition Time:	250 s

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01933-01	64.970 (64.6)	(CN)K⁺	Eggshell proteins
	65.967 (28.2)	(CN)Ca⁺	Eggshell proteins/CaCO₃
	78.958 (27.7)	KNaOH⁺	Eggshell materials
	121.927 (32.1)	(CN)Ca₂O⁺	Eggshell proteins/CaCO₃
	137.922 (28.8)	(CNO)Ca₂O⁺	Eggshell proteins/CaCO₃
	177.888 (46.0)	(CN)Ca₃O₂⁺	Eggshell proteins/CaCO₃
	193.881 (32.2)	(CNO)Ca₃O₂⁺	Eggshell proteins/CaCO₃
	233.846 (36.2)	(CN)Ca₄O₃⁺	Eggshell proteins/CaCO₃
	249.842 (38.2)	(CNO)Ca₄O₃⁺	Eggshell proteins/CaCO₃
	289.807 (39.6)	(CN)Ca₅O₄⁺	Eggshell proteins/CaCO₃
	305.799 (29.6)	(CNO)Ca₅O₄⁺	Eggshell proteins/CaCO₃
	345.762 (28.3)	(CN)Ca₆O₅⁺	Eggshell proteins/CaCO₃
	361.755 (21.6)	(CNO)Ca₆O₅⁺	Eggshell proteins/CaCO₃

Accession #:	01933-01
■ Specimen:	Eggshell White – Kremer Pigmente ref. 11410 – Positive polarity
■ Technique:	SIMS
Instrument:	IONTOF, TOF SIMS IV
Analyzer Type:	Time-of-flight
Analyzer Mass Resolving Power:	2100 m/Δm
Mass Resolving Power Determined at:	27 Da
Species Used for Mass Calibration:	Na⁺, Ca⁺, CaO⁺, Ca₂O⁺, Ca₃O₂⁺, Ca₄O₃⁺, Ca₅O₄⁺, Ca₆O₅⁺
Specimen Normal-to-Analyzer:	0°
Source-to-Analyzer Angle:	45°
Primary Beam Ion Gun:	LMIG
Primary Ion Species:	Bi₃⁺
Primary Ion Dose:	4.37 × 10¹¹ ion/cm²
Primary Ion Pulse Width:	0.8–1.2 ns
Primary Ion Pulse Rate:	5 kHz
Net Beam Voltage:	25 000 eV
Pulsed Beam Current:	0.000 16 nA
DC Beam Current:	15.7 nA
Beam Diameter:	∼2 μm
Beam Raster Size:	250 × 250 μm²
Beam Incident Angle:	45°
Secondary Source Polarity:	Positive
Mass Range Minimum:	0 Da
Mass Range Maximum:	3545 Da
Spectrum Dead Time Corrected:	Yes
Total Spectral Acquisition Time:	250 s
Comment:	Peaks attributed to (CNO)Ca_xO_y⁺ are detected for this material. Additional series of peaks are detected, with lower intensity. They can be attributed to PO₂(CaO)_n⁺ and CNNa(CaO)_n⁺ with n = 2–6 and are likely from the eggshell materials.

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01933-02	26.005 (56.4)	CN⁻	Eggshell proteins
	42.001 (48.5)	CNO⁻	Eggshell proteins
	44.999 (26.2)	CO₂H⁻	CaCO₃/Eggshell materials
	56.965 (−7.63)	CaOH⁻	CaCO₃
	59.987 (27.8)	CO₃⁻	Eggshell materials
	62.966 (28.1)	PO₂⁻	Eggshell materials/Ca₃(PO₄)₂
	66.002 (51.4)	C₃NO⁻	Eggshell proteins
	72.964 (45.1)	CaO₂H⁻	CaCO₃/Ca(OH)₂
	78.963 (52.2)	PO₃⁻	Eggshell materials/Ca₃(PO₄)₂
	89.966 (24.8)	(CaO)(OH)₂⁻	CaCO₃/Ca(OH)₂
	90.974 (23.8)	(CaOH)(OH)₂⁻	CaCO₃/Ca(OH)₂
	99.953 (46.2)	CaCO₃⁻	CaCO₃
	108.974 (14.3)	CaOH(CN)₂⁻	Eggshell proteins/CaCO₃
	115.946 (23.2)	CaOCO₃⁻	CaCO₃
	116.953 (19.7)	CaOHCO₃⁻	CaCO₃
	117.974 (9.87)	Ca(CN)₃⁻	Eggshell proteins/CaCO₃
	124.970 (20.6)	CaO₂H(CN)₂⁻	Eggshell proteins/CaCO₃
	128.920 (9.25)	(CaO)₂(OH)⁻	CaCO₃/Ca(OH)₂
	133.970 (14.9)	CaOC₃N₃⁻	Eggshell proteins/CaCO₃
	146.931 (14.2)	H(CaO)₂(OH)₂⁻	CaCO₃/Ca(OH)₂
	149.968 (35.4)	CaO₂C₃N₃⁻	Eggshell proteins/CaCO₃
	173.938 (43.7)	Ca₂OC₃N₃⁻	Eggshell proteins/CaCO₃
	184.881 (25.6)	Ca₃O₄H⁻	CaCO₃/Ca(OH)₂
	202.889 (−2.97)	H(CaO)₃(OH)₂⁻	CaCO₃/Ca(OH)₂
	240.832 (−6.39)	Ca₄O₅H⁻	CaCO₃

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01934-01	23.983 (−51.8)	Mg⁺	CaMg(CO₃)₂
	64.973 (11.2)	Mg₂OH⁺	CaMg(CO₃)₂
	79.946 (52.6)	CaMgO⁺	CaMg(CO₃)₂
	119.922 (3.37)	CaMg₂O₂⁺	CaMg(CO₃)₂
	135.902 (16.8)	Ca₂MgO₂⁺	CaMg(CO₃)₂
	175.880 (−1.49)	Ca₂Mg₂O₃⁺	CaMg(CO₃)₂
	191.860 (16.7)	Ca₃O₂MgO⁺	CaMg(CO₃)₂
	231.838 (4.73)	Ca₃O₂(MgO)₂⁺	CaMg(CO₃)₂
	247.818 (12.9)	Ca₄O₃MgO⁺	CaMg(CO₃)₂

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01934-02	59.983 (−31.5)	CO₃⁻	CaMg(CO₃)₂
	90.974 (28.0)	(CaOH)(OH)₂⁻	CaMg(CO₃)₂
	99.944 (−35.3)	CaCO₃⁻	CaMg(CO₃)₂
	116.947 (−31.3)	CaHCO₄⁻	CaMg(CO₃)₂
	128.914 (−30.0)	(CaO)₂(OH)⁻	CaMg(CO₃)₂
	136.921 (−15.0)	Ca₂H(CO)₂⁻	CaMg(CO₃)₂
	152.911 (−47.2)	Ca₂OH(CO)₂	CaMg(CO₃)₂

Accession #:	01934-02
■ Specimen:	Dolomite 10 μ – Kremer Pigmente ref. 58740 – Negative polarity
■ Technique:	SIMS
Instrument:	IONTOF, TOF SIMS IV
Analyzer Type:	Time-of-flight
Analyzer Mass Resolving Power:	2000 m/Δm
Mass Resolving Power Determined at:	25 Da
Species Used for Mass Calibration:	Cl⁻, CaO⁻, Ca₂O₃H⁻
Specimen Normal-to-Analyzer:	0°
Source-to-Analyzer Angle:	45°
Primary Beam Ion Gun:	LMIG
Primary Ion Species:	Bi₃⁺
Primary Ion Dose:	4.37 × 10¹¹ ion/cm²
Primary Ion Pulse Width:	0.8–1.2 ns
Primary Ion Pulse Rate:	5 kHz
Net Beam Voltage:	25 000 eV
Pulsed Beam Current:	0.000 16 nA
DC Beam Current:	15.7 nA
Beam Diameter:	∼2 μm
Beam Raster Size:	250 × 250 μm²
Beam Incident Angle:	45°
Secondary Source Polarity:	Negative
Mass Range Minimum:	0 Da
Mass Range Maximum:	3545 Da
Spectrum Dead Time Corrected:	Yes
Total Spectral Acquisition Time:	283 s

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01935-01	64.971 (20.3)	SO₂H⁺	CaSO₄
	71.935 (15.5)	CaS⁺	CaSO₄
	87.904 (−8.75)	Sr⁺	Natural impurities
	87.929 (3.63)	CaSO⁺	CaSO₄
	103.924 (3.64)	CaSO₂⁺	CaSO₄
	104.909 (7.02)	SrOH⁺	Natural impurities
	127.895 (29.5)	Ca₂SO⁺	CaSO₄
	143.887 (2.22)	Ca₂SO₂⁺	CaSO₄
	159.882 (9.09)	Ca₂SO₃⁺	CaSO₄
	183.853 (21.2)	Ca₃SO₂⁺	CaSO₄
	239.813 (26.4)	Ca₄SO₃⁺	CaSO₄
	255.801 (−2.38)	Ca₄SO₄⁺	CaSO₄
	295.770 (20.1)	Ca₅SO₄⁺	CaSO₄

Accession #:	01935-01
■ Specimen:	Anhydrite plaster, burnt gypsum – Kremer Pigmente ref. 58320 – Positive polarity
■ Technique:	SIMS
Instrument:	IONTOF, TOF SIMS IV
Analyzer Type:	Time-of-flight
Analyzer Mass Resolving Power:	2600 m/Δm
Mass Resolving Power Determined at:	27 Da
Species Used for Mass Calibration:	Na⁺, Ca⁺, CaO⁺, Ca₂O⁺, Ca₃O₂⁺, Ca₄O₃⁺, Ca₅O₄⁺, Ca₆O₅⁺
Specimen Normal-to-Analyzer:	0°
Source-to-Analyzer Angle:	45°
Primary Beam Ion Gun:	LMIG
Primary Ion Species:	Bi₃⁺
	4.34 × 10¹¹ ion/cm²
Primary Ion Pulse Width:	0.8–1.2 ns
Primary Ion Pulse Rate:	5 kHz
Net Beam Voltage:	25 000 eV
Pulsed Beam Current:	0.000 21 nA
DC Beam Current:	14.6 nA
Beam Diameter:	∼2 μm
Beam Raster Size:	250 × 250 μm²
Beam Incident Angle:	45°
Secondary Source Polarity:	Positive
Mass Range Minimum:	0 Da
Mass Range Maximum:	3545 Da
Spectrum Dead Time Corrected:	Yes
Total Spectral Acquisition Time:	210 s
Comment:	The detection of strontium in both gypsum samples is noteworthy, as it is an element found in natural gypsum.⁶ Anhydrite and gypsum share almost identical ToF-SIMS spectra.

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01935-02	15.995 (−14.9)	O⁻	–
	31.972 (−6.76)	S⁻	–
	34.968 (−34.1)	Cl⁻	Natural impurities
	47.965 (−45.3)	SO⁻	CaSO₄
	59.965 (−32.2)	SiO₂⁻	Natural impurities
	63.964 (31.0)	SO₂⁻	CaSO₄
	75.965 (42.2)	SiO₃⁻	Natural impurities
	79.956 (−11.7)	SO₃⁻	CaSO₄
	90.967 (−38.5)	CaO₃H₃⁻	CaSO₄
	95.948 (−39.7)	SO₄⁻	CaSO₄
	103.926 (9.26)	CaSO₂⁻	CaSO₄
	119.917 (−21.2)	CaSO₃⁻	CaSO₄
	128.919 (3.63)	Ca₂O₃H⁻	CaSO₄
	135.910 (−33.0)	CaSO₄⁻	CaSO₄
	144.898 (15.9)	SO₂HCa₂⁻	CaSO₄
	152.915 (−16.9)	CaSO₅H⁻	CaSO₄
	160.896 (32.2)	SO₃HCa₂⁻	CaSO₄
	167.882 (−27.5)	CaS₂O₄⁻	CaSO₄
	176.891 (32.2)	SO₄HCa₂⁻	CaSO₄
	183.876 (−30.1)	CaS₂O₅⁻	CaSO₄
	192.875 (−25.2)	SO₅HCa₂⁻	CaSO₄
	199.870 (−31.6)	CaS₂O₆⁻	CaSO₄
	208.865 (34.6)	Ca₂S₂O₄H⁻	CaSO₄
	216.859 (−11.1)	CaHS₃O₅⁻	CaSO₄
	224.848 (−16.8)	Ca₂S₂O₅H⁻	CaSO₄
	232.851 (−24.9)	CaHS₃O₆⁻	CaSO₄
	240.837 (−41.3)	Ca₂S₂O₆H⁻	CaSO₄
	264.821 (−28.9)	CaHS₄O₆⁻	CaSO₄
	280.820 (−14.4)	CaOHS₄O₆⁻	CaSO₄

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01936-01	64.970 (14.3)	SO₂H⁺	CaSO₄
	71.935 (12.3)	CaS⁺	CaSO₄
	87.906 (12.5)	Sr⁺	Natural impurities
	87.929 (−3.64)	CaSO⁺	CaSO₄
	103.923 (−11.6)	CaSO₂⁺	CaSO₄
	104.910 (20.7)	SrOH⁺	Natural impurities
	127.895 (25.8)	Ca₂SO⁺	CaSO₄
	143.887 (1.37)	Ca₂SO₂⁺	CaSO₄
	159.884 (13.4)	Ca₂SO₃⁺	CaSO₄
	183.853 (20.5)	Ca₃SO₂⁺	CaSO₄
	239.812 (20.2)	Ca₄SO₃⁺	CaSO₄
	255.806 (16.8)	Ca₄SO₄⁺	CaSO₄
	295.772 (26.6)	Ca₅SO₄⁺	CaSO₄

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
01936-02	15.995 (−7.16)	O⁻	–
	31.972 (−25.2)	S⁻	–
	34.968 (−44.1)	Cl⁻	Natural impurities
	47.965 (−47.8)	SO⁻	CaSO₄
	59.966 (−27.1)	SiO₂⁻	Natural impurities
	63.963 (15.6)	SO₂⁻	CaSO₄
	75.965 (30.0)	SiO₃⁻	Natural impurities
	79.955 (−25.7)	SO₃⁻	CaSO₄
	90.968 (−33.0)	CaO₃H₃⁻	CaSO₄
	95.948 (−41.0)	SO₄⁻	CaSO₄
	103.923 (−19.5)	CaSO₂⁻	CaSO₄
	119.916 (−29.8)	CaSO₃⁻	CaSO₄
	128.918 (−1.46)	Ca₂O₃H⁻	CaSO₄
	135.909 (−39.0)	CaSO₄⁻	CaSO₄
	144.896 (5.45)	SO₂HCa₂⁻	CaSO₄
	152.915 (−15.2)	CaSO₅H⁻	CaSO₄
	160.896 (35.5)	SO₃HCa₂⁻	CaSO₄
	167.880 (−38.4)	CaS₂O₄⁻	CaSO₄
	176.888 (13.6)	SO₄HCa₂⁻	CaSO₄
	183.874 (−38.3)	CaS₂O₅⁻	CaSO₄
	192.875 (−21.5)	SO₅HCa₂⁻	CaSO₄
	199.871 (−24.0)	CaS₂O₆⁻	CaSO₄
	208.862 (22.0)	Ca₂S₂O₄H⁻	CaSO₄
	216.858 (−15.6)	CaHS₃O₅⁻	CaSO₄
	224.853 (1.88)	Ca₂S₂O₅H⁻	CaSO₄
	232.851 (−18.6)	CaHS₃O₆⁻	CaSO₄
	240.841 (−22.0)	Ca₂S₂O₆H⁻	CaSO₄
	264.822 (−24.7)	CaHS₄O₆⁻	CaSO₄
	280.820 (3.40)	CaOHS₄O₆⁻	CaSO₄

Accession #:	01936-02
■ Specimen:	Natural alabaster plaster – Kremer Pigmente ref. 58340 – Negative polarity
■ Technique:	SIMS
Instrument:	IONTOF, TOF SIMS IV
Analyzer Type:	Time-of-flight
Analyzer Mass Resolving Power:	2400 m/Δm
Mass Resolving Power Determined at:	25 Da
Species Used for Mass Calibration:	Cl⁻, CaO₂H⁻, Ca₂O₃H⁻
Specimen Normal-to-Analyzer:	0°
Source-to-Analyzer Angle:	45°
Primary Beam Ion Gun:	LMIG
Primary Ion Species:	Bi₃⁺
Primary Ion Dose:	4.34 × 10¹¹ ion/cm²
Primary Ion Pulse Width:	0.8–1.2 ns
Primary Ion Pulse Rate:	5 kHz
Net Beam Voltage:	25 000 eV
Pulsed Beam Current:	0.000 21 nA
DC Beam Current:	14.6 nA
Beam Diameter:	∼2 μm
Beam Raster Size:	250 × 250 μm²
Beam Incident Angle:	45°
Secondary Source Polarity:	Negative
Mass Range Minimum:	0 Da
Mass Range Maximum:	3545 Da
Spectrum Dead Time Corrected	Yes
Total Spectral Acquisition Time:	210 s
Comment:	Anhydrite and gypsum share almost identical ToF-SIMS spectra.

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
All	39.96 (13.4)	Ca⁺	All white pigments containing calcium
	56.94 (8.77)	CaOH⁺	All white pigments containing calcium
	95.92 (11.0)	Ca₂O⁺	All white pigments containing calcium
	111.92 (13.4)	Ca₂O₂⁺	All white pigments containing calcium
	112.93 (13.4)	Ca₂O₂H⁺	All white pigments containing calcium
	151.879 (13.1)	Ca₃O₂⁺	All white pigments containing calcium
	167.874 (7.62)	Ca₃O₃⁺	All white pigments containing calcium
	168.882 (11.1)	Ca₃O₃H⁺	All white pigments containing calcium
	207.836 (7.75)	Ca₄O₃⁺	All white pigments containing calcium
	223.831 (11.3)	Ca₄O₄⁺	All white pigments containing calcium
	224.84 (11.7)	Ca₄O₄H⁺	All white pigments containing calcium
	263.79 (11.3)	Ca₅O₄⁺	All white pigments containing calcium
	279.79 (9.29)	Ca₅O₅⁺	All white pigments containing calcium
	280.79 (12.0)	Ca₅O₅H⁺	All white pigments containing calcium
	319.75 (6.54)	Ca₆O₅⁺	All white pigments containing calcium
	335.74 (13.3)	Ca₆O₆⁺	All white pigments containing calcium
	336.75 (12.1)	Ca₆O₆H⁺	All white pigments containing calcium
	375.71 (5.43)	Ca₇O₆⁺	All white pigments containing calcium
	391.73 (2.18)	Ca₇O₇⁺	All white pigments containing calcium
	392.72 (21.1)	Ca₇O₇H⁺	All white pigments containing calcium

Spectrum ID #	Mass (Δm), Da	Species	Peak Assignment
All	55.96 (11.0)	CaO⁻	All white pigments containing calcium
All	71.96 (20.9)	CaO₂⁻	All white pigments containing calcium

Tof-SIMS spectra of historical inorganic pigments: Calcium white pigments in both polarities Open Access

INTRODUCTION

SPECIMEN DESCRIPTION (ACCESSION # 01931)

SPECIMEN DESCRIPTION (ACCESSION # 01932)

SPECIMEN DESCRIPTION (ACCESSION # 01933)

SPECIMEN DESCRIPTION (ACCESSION # 01934)

SPECIMEN DESCRIPTION (ACCESSION # 01935, 01936)

INSTRUMENT CONFIGURATION

■ Ion sources

Ion source 1 of 2

Ion source 2 of 2

ACKNOWLEDGMENTS

AUTHOR DECLARATIONS

Conflict of Interest

Author Contributions

DATA AVAILABILITY

REFERENCES

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Tof-SIMS spectra of historical inorganic pigments: Calcium white pigments in both polarities