Koppartvål Möjligheterna att isolera mässing från läder och därigenom förhindra att tvål uppstår

Abstract

Objects where brass and leather are combined with each other often lead to the brass corroding heavily and turning green. This type of corrosion product is called copper soap and can occur even when the object is stored at low relative humidity (RH) of 30 %. What happens is that the hydrogen ions in carboxylic acids (fatty acids) associated with the leather are replaced by copper ions from the brass. It takes contact between the two materials for this to occur, why the question was asked if the brass in some way could be isolated from the leather. An experimental study was made of the insulation capability of the polyester material Melinex. Eight leather samples were prepared with brass rings around the leather treated with three different fats: lanolin, olive oil and the commercial product Ekol oil. In three of the samples the brass was isolated from the leather by placing a film of the Melinex between the two materials. The rings were examined by energy dispersive x-ray spectroscopy (SEM-EDX), which showed that they were brass. The leather was investigated with ferritest and vanillin test, which found out that it, was tanned with hydrolysable vegetable tanning agents. Copper soap was simulated in a climate chamber with near 100 % RH and at room temperature for four weeks. The samples without Melinex showed green corrosion while those with Melinex did not. Raman spectroscopy, however, did not prove that it was specifically copper soap. A study using Fourier Transform Infrared Spectroscopy (FTIR) showed that it was both copper and zinc soap that had formed. SEM-EDX analysis showed that no copper ions penetrated the leather structure when Melinex were used as insulation.