Although formaldehyde was found to be the most effective fumigant, it is usually used in an aqueous solution, 60% water, which is deleterious to art objects to be fumigated. Paraformaldehyde (PF) was tested as a fumigant in order to avoid the effects of water. Evaporation of PF is a problem for the apparatus that heats it under reduced pressure. For complete sterilization, 20-50 grams of PF/m³ were required against common fungi and 50-70 grams of PF/m³ against tonophilous fungi. During the experiment, it was also found that PF might crystallize out when more than 20 grams of PF/m³ were applied for fumigation. To avoid such crytallization PF was mixed with a solution of methacrylic resin and celluloid and evaporated to form a film (designated as PF paper). The PF paper prevented spore germination on lenses and prisms: even after 20 years, all glassy parts were entirely free from cloudiness resulting from fungal growth. See also IIC Abstracts 1-680.