Acrylate varnishes are due to their suitable properties frequently used in restoration and preservation on variety of historical objects and materials. Common practice of their application involves using as an adhesive agents, consolidants and protective coatings. The purpose of protective coatings especially on metal artefacts is to reduce access of pollutants to the surface of the artefact. In this paper, coatings prepared from two acrylate polymers Paraloid B72 and Paraloid B48N are compared in terms of permeability for water and level of protective properties against air pollutants. For this purpose, electrochemical impedance spectroscopy and resistometric method were chosen for analysis of the coatings. Obtained results show lower permeability for water in case of Paraloid B72. However, same coating provided lower protection against air pollutants than Paraloid B48N coating.

Restoration treatment, specimen preparation or mass loss measurements on coupons made of lead require a reliable process of dissolution of corrosion products. In this study, several types of model corrosion products with compositions representative of those found on real objects were prepared and characterized. Ten solutions were then thoroughly tested in interval cleaning experiments, regarding the efficiency of removal of the corrosion products, corrosivity towards bare lead, and remnants left on the surface. The solution recommended in the current version of the ISO 8470 standard was found to be improper for the cleaning of both historical artefacts and corrosion coupons due to its inability to remove sulfide corrosion products and the risk of surface contamination and staining. A solution of 20% hydrochloric acid is the best choice for the preparation of lead coupons before exposure or for evaluation of mass loss of exposed samples because its somewhat higher corrosivity towards metallic lead is tolerable for these applications. Rochelle salt solution was found to be optimal for the cleaning of historical artefacts free of sulfide corrosion products due to the lowest corrosivity. None of these alternative solutions leave remnants on the surface and they are efficient at laboratory temperature.

Lead corrosion products can undergo certain changes over the time in terms of composition. How these changes affect the corrosion of the underlying lead is an important question for protection of historical lead artefacts. In this work, we focus on characterization of changes in composition of lead corrosion products and how the composition affects corrosion of the lead substrate. Prepared model corrosion products on lead coupons were exposed to air at different relative humidity and concertation of acetic acid vapours. Composition of the corrosion products was analysed by XRD and corrosion rate was calculated from gravimetric data. Measurement of polarization resistance was implemented to get more insight into the protective ability of formate corrosion products. With lead formate covering the surface, the corrosion rate of lead coupons was minimal even in humid air with 400 ppb of acetic acid vapours. Acetic acid was however able to alter lead carbonate corrosion products resulting in increased corrosion rate.

Sixteen localities were involved in a broad study, resulting in the classification of the indoor corrosivity of metals considered in the ISO 11844 standard, especially lead. Recently, lead has been added to the standard as a metal specifically sensitive to volatile organic compounds such as acetic acid. Data on one-year exposure in museum depositories and exhibition spaces, archives, libraries, and churches show that the currently valid lead corrosivity categories are not correctly defined. The obtained data allowed for the proposal of new realistic ranges of indoor corrosivity categories for lead. The exposure program was also used to validate techniques for determining the corrosion degradation of metal coupons. Mass increase and mass loss techniques were supplemented with the galvanostatic reduction technique and the measurement of color changes. The study identified the limitations of the mass gain method. Not only is the galvanostatic reduction technique applicable for silver and copper coupons, but the build-up of reducible lead corrosion products depends on air corrosivity. CIELab color-change measurement has proven to be a simple and easy-to-apply method for monitoring the corrosivity of indoor atmospheres with regard to lead. A more reliable response is provided by the determination of color change after 3 months of exposure rather than after one year.

Many studies of silver corrosion have been focused on indoor sulfur-containing atmospheres. However, significant corrosion damage of silver can also occur in the presence of other corrosion stimulants, such as halides, pseudohalides, or thiourea. These environments pose a specific threat for historical silver objects like daguerreotypes or coins, for example, during incorrect storing or cleaning method. To better characterize the silver corrosion caused by the solutions, electrochemical impedance spectroscopy (EIS) and electrical resistance technique were used. EIS measurements show that the dissolution of silver in tested solutions is mainly controlled by diffusion, suggesting the formation of a layer on the sample surface. For the electrical resistance technique, two different setups with electrical resistance probes were used: in saturated solutions and in atmospheric conditions simulating corrosion under deposits. In the latter setup, the corrosion rates decreased after a certain amount of time which can be explained by the presence of a salt layer (as suggested from EIS results). Regardless of the arrangement, cyanide and thiourea environment resulted in the highest corrosion rates.