For stiffening materials that will be exposed to damp, a solution similar to that used for stiffening hats is suitable. This is composed of 5 parts shellac and 1 part borax, with sufficient water. A useful water-proofing material may be made by dissolving shellac in ammonia. A good stiffening waterproofing material is boiled linseed oil, which stiffens by exposure to air and is very pliable. Another waterproofing substance may be applied by passing the materials through a soap bath and afterwards through alum solution; this produces an alumina soap in the fibres and stiffens the fabrics.