Development of a GC–MS strategy for the determination of cross-linked proteins in 20th century paint tubes

•A technical study of paints based on ovalbumine-drying oil mixtures is carried out.•Detection of proteins can be hampered when these are applied in mixture with drying oils.•A new procedure with two hydrolysis steps was implemented for GC–MS analysis of proteins.•Ovalbumine affects the curing of linseed oil.•Hypothesis on copolymeristaion between drying oils and ovalbumine is proposed.