This article summarizes research into the stabilization of rag paper (ca. 1899) through immersion treatment with 100 mM sodium and tetraethylammonium borohydride. The effect of prior aqueous deacidification with magnesium bicarbonate upon the permanence of cellulose was also explored. Data were obtained through analysis (viscometric average degree of polymerization using the solvent cadoxen) of treated samples before and after humid accelerated thermal aging (70°C, 50% relative humidity for 84 days). Results demonstrated that borohydride treatments can significantly improve the long-term stability of cellulose. Data analysis revealed the importance of removing ketone and aldehyde carbonyls from oxidized cellulose prior to viscometric analysis with alkaline cellulose solvents.