Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/18

 BLISTERING OF PAINT.

In the following lines are laid down some general rules that govern this phenomenon, and from the same draw some practical conclusions, the object of which will be to set the question at rest. The blistering of paint is in a large measure traceable to the position of the surface, it is usually found on work presenting a south aspect, or exposed to the full rays of the sun. As a defect it is associated with the summer season, winters being opposed to its action. The deduction to be drawn from this is that it is the effect of heat. Paint is a body both mineral and metallic, made into a plastic condition by oil, the object of which is to keep out the moisture from exposed surfaces in buildings, and to offer on internal work a uniform and pleasing surface to the eye. The oil used is linseed, which by boiling attains setting or drying qualities and becomes better by keeping, its thick or heavy nature when loaded with mineral and metallic matters being reduced for working purposes by spirits of turpentine, a volatile spirit that is a mere aid to the spreading of paint. Paint so largely composed of oil will never fairly set or assume a dry state. However dry and brittle if: may appear, it is capable of being rendered soft and plastic by the application of heat, and hence the hand stove of the painters is the most ordinary instrument for the removal of old paint. We mention this, for it is clear that, approach the subject as we will, we find heat the prime cause of the blistering of paint. Closing in with the subject, and bringing it into narrower lines, blistering, properly speaking, is wholly confined to wood as a base or groundwork. It is true it is not unknown to iron or plaster, but in these cases it is variant in form, and not blistering in the true sense of the term. The blistering of paint on iron is not traceable to