Download Portable XRF for Pigment Analysis of Multiple Paint Layers

Portable XRF
for Pigment Analysis
of Multiple Paint Layers
Hanne Moltubakk Kempton (NIKU, conservator)
Susanne Kaun (NIKU, conservator)
Outline
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Architectural paint research
Portable XRF - our equipment
Method
Results and discussion
Conservator investigating a historical interior
Ongoing research project:
Portable XRF as an Investigation and Documentation Method in the
Field of Architectural Paint Research of Interiors
- A Feasibility and Application Study
Can XRF give useful information in architectural paint research?
Architectural paint research
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The study of how historic
interiors and exteriors have
changed over time
Methods
6. Present colour
5. layer
4. layer
3. layer
2. layer
1. layer
Why do we need to identify of pigments?
Colours often change
over time
Pigments can help
dating
Lead white
Zinc white
Titanium white
PbCO3 Pb(OH)2
ZnO
TiO2
Used from antiquity to
20th century
Used from ~ 1840
Used from ~ 1910
Chemical analysis of pigments
Pigment analysis with SEM-EDX
Pb, As, Ca, Fe, S?
Lead white 2PbCO3·Pb(OH)2
Orpiment As2S3
Iron oxide FeO
Gypsum/chalk CaSO4 /CaCO3
Portable XRF – our equipment
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Niton XL3t GOLDD+
Silicon drift detector
Ag-x-ray tube
50kV/200µA
8 and 3 mm spot
6 settings, 4 automatic filters: Al, Cu, Mo, Fe
CCD camera
Chargeable battery
1,6 kg
Detector handles depending on voltage up to
200 000 cps
 Solution: down to 160 eV
Method:
Working in situ
Method: Interpretation of the data
1.
Spectra: Which elements are in the sample?
Elements in the sample  effects within the sample and the instrument
2.
Elements: Which pigment has been used?
Realgar, As4S4
Arsenic and sulfur
>
Orpiment, As4S6
XRF can not distinguish between pigments with the same elements and
different chemical bonding
Elements identified by XRF:
 Hg, Pb, S?
Interpretation:
 Sulphur is overlapped by lead
 Vermillion (HgS)
 Read lead (Pb3O4) or/and
lead white (2PbCO3·Pb(OH)2)
Door in the library, Barony in Rosendal, 17th century.
Preliminary results
Can XRF give useful information in architectural paint research?
Yes, in field study
of simpler structures
The challenge is the multilayered structures
As, Pb
18th century wall paper at Hafslund hovedgård
Preliminary results
Can XRF give useful information in
architectural paint research?
XRF on multi-layered structures
presents us with a problem
 The XRF measures several
layers in one go
 We are interested in one
layer at a time
7
6
5
4
3
2
1
Identification of some pigments
Some pigments have distinctive elements and can be assigned to a specific layer
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Iron oxide (Fe)
Vermilion (Hg)
Cadmium pigments (Cd)
Lead tin yellow (Sn)
Chrome yellow (Cr)
Orpiment (As)
Cobalt blue (Co)
Fe indicates iron oxide in
the upper layer
#8
#7
#6
#5
#2
Vardøhus fortress
18th century
Transition from using lead white to zink white
Pb
Gjetemyren manor, 18th century
Transition from using lead white to zink white
Zn
Gjetemyren manor, 18th century
Pb
Transition from using lead white to zink white
Zn
Gjetemyren manor, 18th century
Pb
Transition from using lead white to zink white
Zn
Gjetemyren manor, 18th century
Pb
Summary
 Identification of inorganic pigments in simple structures
 Identification of pigments with distinctive elements in multiple
layered structures
 Replace sampling in same cases
 Still uncertainties when it comes to multiple layered structures
Acknowledgements
The Norwegian X-ray conference
Arne Bjerklund and Torfinn Fongen (HolgerHartmann)
Colleagues at Norwegian Institute for cultural heritage research (NIKU)
[email protected]
[email protected]