who did a detailed analysis in 1933 to revealed that earlier restorers had " acted with a great deal of restraint " ?
A decision was made that all of the shadowy layer of animal glue and " lamp black " , all of the wax , and all of the overpainted areas were contamination of one sort or another : smoke deposits , earlier restoration attempts and painted definition by later restorers in attempt to enliven the appearance of the work .