Preparation and characterization of Zinc metal soap from shea butter (Vitellaria paradoxa)

Zinc metal soaps are of great importance in the manufacture of personal care products and other industrial applications. Variations in the soaps and their properties are usually due to the type of oil used in the synthesis. Shea butter (Vitellaria paradoxa), being a valuable industrial raw material, was investigated for the synthesis of zinc metal soap. Locally obtained shea butter was characterized, refined and used to synthesize metal soap of zinc which was characterized. The zinc soap produced exhibited an off-white appearance, pH of 7.8, non-foaming, and no free alkalinity present. The functional groups in the soap were confirmed by FTIR.

Fatty Acids and Their Metal Salts: A Review of Their Infrared Spectra in Light of Their Presence in Cultural Heritage

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.

Formation of Metal Soaps In Oil Paintings Under Variable Environmental Conditions

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.

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

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.

Effects of metal ions and wood pitch on retention and physical properties of TMP

The influence of metal ions, {\mathrm{Ca}^{2+}} and {\mathrm{Mg}^{2+}}, on wood pitch retention at pH 8 was studied by investigating the pitch content of TMP-papers using both short- and long-column gas chromatography (GC). The effects of two different drying methods, air-drying and freeze-drying, on pitch retention were also compared in this work. The pitch emulsion was prepared with fatty acids, resin acids, and triglycerides at a certain ratio to simulate the pitch composition in closed water system in paper mill. At increasing pH, some of the resin and fatty acids will dissolve into the water phase as metal soaps. In this work, the retention of colloidal pitch in TMP-papers by metal ions at pH 8 was determined. The amount of 5 mM metal ions was found to retain more pitch. The tensile index decreased by the addition of metal ions, and the decrease became more pronounced as the increase of the metal ions concentration. Besides, the hydrophobicity of handsheets was found being changed only a little, which might because the morphology and pitch retained on the surface both affected the hydrophobicity.

Insight into the effects of moisture and layer build-up on the formation of lead soaps using micro-ATR-FTIR spectroscopic imaging of complex painted stratigraphies

Metal soaps are formed in paint layers thorough the reaction of metal ions of pigments and fatty acids of organic binders. In this study, micro-ATR-FTIR spectroscopic imaging was used to analyse the formation of lead soaps in oil-based paint layers in relation to their exposure to moisture sources. The investigations were carried out on authentic samples of complex stratigraphies from cold painted terracotta statues (Sacred Mount, Varallo, UNESCO) and different IR-active lead white pigments, organic materials, and lead soaps were discriminated. The saponification of selected paint layers was correlated to the conservation history, the manufacturing technique, and the build-up of layers. The presence of hydrophilic layers within the stratigraphy and their role as a further water source are discussed. Furthermore, the modifications experienced by lead-based pigments from the core of an intact grain of pigment towards the newly formed decay phases were investigated via a novel approach based on shift of the peak for the corresponding spectral bands and their integrated absorbance in the ATR-FTIR spectra. Qualitative information on the spatial distribution from the chemical images was combined with quantitative information on the peak shift to evaluate the different manufacture (lead carbonate, basic lead carbonate) or the extent of decay undergone by the lead-based pigments as a function of their grain size, contiguous layers, and moisture source. Similar results, having a high impact on heritage science and analytical chemistry, allow developing up-to-date conservation strategies by connecting an advanced knowledge of the materials to the social and conservation history of artefacts.

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

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.