A Critical Review on the Analysis of Metal Soaps in Oil Paintings

In a cultural heritage context, fatty acids are usually found as breakdown products of lipid-containing organic remains in archaeological findings, binders in aged oil paintings, and additives in modern art-related materials. They may further interact with the ionic environment transforming into metal soaps, a process that has been recognized as a threat in aged paintings but has received less attention in archaeological objects. The investigation of the above related categories of materials with infrared spectroscopy can provide an overall picture of the organic components’ identity and demonstrate their condition and prehistory. The capability of investigating and distinguishing fatty acids and their metal soaps through their rich infrared features, such as the acidic carbonyl, the carboxylate shifts, the variable splits of alkyl chain stretching, bending, twisting, wagging, and rocking vibrations, as well as the hydroxyl peak envelopes and acid dimer bands, allows for their direct detailed characterization. This paper reviews the infrared spectra of selected saturated fatty monoacids and diacids, and their corresponding sodium, calcium, and zinc salts and, supported by newly recorded data, highlights the significance of their spectroscopic features.

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Drying Oil and Natural Varnishes in Paintings: A Competition in the Metal Soap Formation

Coatings ◽

10.3390/coatings11020171 ◽

2021 ◽

Vol 11 (2) ◽

pp. 171

Author(s):

Tommaso Poli ◽

Oscar Chiantore ◽

Eliano Diana ◽

Anna Piccirillo

Keyword(s):

Paint Film ◽

Metal Soap ◽

Oxidation Processes ◽

Oil Paintings ◽

Drying Oil ◽

Formation Kinetics ◽

Natural Resins ◽

Metal Soaps ◽

Main Components ◽

Hydrolysis Of

Metal soaps formation is a well-known issue in oil paintings. Along the lifetime of the painting, carboxylic acids coming from drying oil (free fatty acids, acids from hydrolysis of triglycerides and from oxidation processes) can react with cations of some pigments (in particular, smalt, lead white and zinc white) forming the related carboxylic salts. As observed by many authors, the formation of these carboxylates, with the tendency to migrate and to aggregate, not only modifies the behavior and the aspect of the paint film but also complicates the cleaning approach. In previous works we have demonstrated that a similar pigment reactivity is possible even in presence of natural resins (such as colophony, dammar, mastic, etc) historically used as final varnishes on paintings. In this case, in the reactions the terpenic acids, among the main components of the resins, are involved. In this work, the carboxylates formation kinetics has been studied starting from two representative acids (palmitic and abietic) of painting oils and natural varnishes. Successively, the reactivity of the palmitic acid with the potassium abietate and of the abietic acid with the potassium palmitate has been verified. This investigation aims at clarifying in which way terpenic acids can be involved in the metal soaps reactivity confirming that also surface varnishes may play a significant role in the carboxylates formation and reactivity. It is important to keep in mind that a finishing varnish can be removed and reapplied many times during the lifetime of a painting, thus renewing the provision of reactive terpenic acids at the interface of the painted layers.

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The influence of commercial primed canvases in the manifestation of metal soaps protrusions in Georgia O’Keeffe’s oil paintings

Heritage Science ◽

10.1186/s40494-020-00451-7 ◽

2020 ◽

Vol 8 (1) ◽

Author(s):

Annette S. Ortiz Miranda ◽

Dale Kronkright ◽

Marc Walton

Keyword(s):

Fatty Acids ◽

Free Fatty Acids ◽

Santa Fe ◽

Metal Carboxylates ◽

Similar Morphology ◽

Oil Paintings ◽

Different Types ◽

Georgia O'keeffe ◽

Ft Ir ◽

Metal Soaps

Abstract During a routine condition survey in 2007 at the Georgia O’Keeffe Museum in Santa Fe, micro-protrusions were found scattered across the surfaces of the artist’s oil paintings produced between 1920 and 1950. In many of her works, including Pedernal (1941) and A Man from the Desert (1941), lead soaps were found aggregated at the painting surface, forcing the surrounding paint to deform into pin-sized protrusions. The structure and composition of the protrusions was analyzed to determine why they formed. Microsamples were removed from four of O’Keeffe’s paintings and investigated using a combination of SEM–EDX, GC–MS, and FT-IR. The combined GC–MS and FT-IR results indicate that the protrusions contain primarily lead carboxylates. The results obtained for a series of ground samples removed from four different paintings were then compared with samples collected from a commercially pre-primed canvas roll found in the artist’s house in Ghost Ranch, NM. We identified two different types of canvases: i) a commercially pre-primed canvas and ii) artist primed canvas. This commercially pre-primed canvas roll has a similar morphology to the ground layers in her paintings that contain protrusions additionally these grounds were found to contain an excess of free fatty acids and metal carboxylates (lead soaps) based on a comparison to canvases the artist primed herself. Based on the analytical results from the four paintings and the commercial pre-primed canvas, we concluded that the artist’s use of this particular commercially pre-primed canvas between 1920 and 1950 play an important role in the observed micro-protrusions.

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Formation of Metal Soaps In Oil Paintings Under Variable Environmental Conditions

10.21203/rs.3.rs-667290/v1 ◽

2021 ◽

Author(s):

M. Piovesan ◽

Marta Pérez-Estébanez ◽

M. San Andrés-Moya

Keyword(s):

Relative Humidity ◽

Environmental Conditions ◽

Metal Soap ◽

Oil Paintings ◽

Lead And Zinc ◽

Temperature Ageing ◽

Lead Zinc ◽

Metal Soaps ◽

Titanium White ◽

Cold Pressed

Abstract Formation of metal soaps in model paintings under cyclic temperature and relative humidity conditions has been studied by ATR-FTIR and compared with the standard controlled conditions generally maintained in many museums and storerooms. Three different white pigments (lead, zinc and titanium white) and two types of linseed oils (cold-pressed and alkali-refined) have been tested. The behaviour in short times (up to 6 weeks) depends on the pigment and environmental conditions. The relative humidity conditions have been shown to influence the metal soap formation in more degree than the temperature. Ageing under low cyclic relative humidity (30-50%) promotes metal soap formation in both lead and zinc white pigments, compared to high relative humidity (50-90%) conditions. Besides, the formation of zinc soaps continues for 6 weeks when low cyclic relative humidity is used, but it stops after 3 weeks under the other ageing conditions studied.

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Microspectroscopic Investigation of Metal Soaps in Oil Paintings--a Case Study on late 19th Century Cobalt Green ((CoxZn1-xO) Paint

Microscopy and Microanalysis ◽

10.1017/s1431927618011248 ◽

2018 ◽

Vol 24 (S1) ◽

pp. 2152-2153

Author(s):

Xiao Ma ◽

Selwin Hageraats ◽

Victoria Beltran ◽

Mathieu Thoury ◽

Matthieu Refregiers ◽

...

Keyword(s):

19Th Century ◽

Late 19Th Century ◽

Oil Paintings ◽

Metal Soaps

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Semi-synthesis as a tool for broadening the health applications of bioactive olive secoiridoids: a critical review

Natural Product Reports ◽

10.1039/d0np00084a ◽

2021 ◽

Author(s):

Manuela Oliverio ◽

Monica Nardi ◽

Maria Luisa Di Gioia ◽

Paola Costanzo ◽

Sonia Bonacci ◽

...

Keyword(s):

Critical Review ◽

Natural Compounds ◽

Effective Strategy ◽

Synthetic Analogues ◽

Health Applications ◽

Natural And Synthetic

Semi-synthesis is an effective strategy to obtain both natural and synthetic analogues of the olive secoiridoids, starting from easy accessible natural compounds.

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