Detection of Gypsum and Syngenite in Gelatine-Alum Sized Papers by ATR-IR and Raman Measurements

Abstract ATR-IR and Raman spectroscopic measurements were used to detect deposits of gypsum CaSO 4 ·2H 2 O and syngenite K 2 Ca(SO 4 ) 2 ·H 2 O in four handmade, gelatine-sized papers from about 1750 to 1850. The formation of gypsum and syngenite can be related to the use of potash alum (potassium aluminium sulphate (KAl(SO 4 ) 2 ·12H 2 O)) in the gelatine sizing of paper. The precise date of the introduction of alum in papermaking is still debated by paper historians due to lack of written evidence. Therefore, paper historians must rely on the examination of historical paper specimens themselves to find hints for the use of alum. Because the aluminium ions of alum are consumed in the sizing process, it is unlikely to find alum itself in historical papers. The detection of gypsum and especially of the potassium containing syngenite can indirectly confirm the use of alum and can help to find gelatine-alum sized papers from the earliest possible period.