Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/159

Rh blisters will be full of discolored water which stains the paint when they break, and upon removing the paint over the blisters it will be found that there is very little, if any, paint or oil left in the grain of the wood. When examining surfaces where the water or dampness is not perceptible at the time of the examination, it is safe to assume, without fear of an error in judgment, that dampness has been the cause of the trouble, but there are also many other causes for paint blistering which are often laid to the foregoing.

Where linseed oil has been used from the bottom of a tank and the settlings or foots are mixed with the paint, it will cause blistering. This has the appearance of dampness, there being spots where the paint has not penetrated and the surface is almost bare. This paint will sometimes pull away in large blisters, the underneath of which show that the paint has adhered to the surface but contained something which would not allow of solid drying. This trouble can be attributed to non-drying mucilaginous matter which separated from the linseed oil and did not allow of uniform penetration, binding or drying. Such blisters are invariably oblong and follow the grain of the wood.

New linseed oil will often cause the paint to blubber in very warm weather, these blubbers causing small blisters, that is attributed to the moisture in the oil which the heat draws out in the shape of different sized blubbers, breaking and forming small blisters when the paint is dry.

Paint mixed with rosin oil will blister under extreme heat. Paint applied over old work blisters more often from the application of excessive oil coats than from any other cause outside of dampness. As stated before, dampness is easily traced in either old or new work. Numerous coats of oil paint will often blister very soon after the paint has been applied. The back of these blisters will show that the paint has at one time been dry and was hard enough to hold to the surface, but when paint was applied over it, it could