Postulate No. 1--The organic linoxyn or semi-elastic binder of the paint vehicle (unlike the cement binder) is perishable and its purity, strength and protection from attack means life to the paint coating, and hence the _life_ of the oil is the _life_ of the paint. Postulate No. 2--The inorganic or powdered mineral solids of a paint coating will crumble unless held together by the binder, but the imperishable pigments must be so ground and blended in the binder that they will protect the binder and present the greatest possible solid front to the atmospheric attack. * * * * * A paint, to secure the greatest protection and life for the linoxyn, together with the durable qualities of cement, _Therefore_ Should expose to air decay within limits of physical strength |within limits required for elasticity, The greatest amount of pigm't material |etc. The least amount of exposed |linoxyn (which is) | or Durable and with the inert qualities of|Considering the linoxyn present be- natural mineral |tween pigment particles as the void |or point of attack, | Then |the minimum exposure of linoxyn or minimum voids obtainable by proportioned pigments of different particle sizes. Law No. 2--The law of the flat arch in paint coatings--i.e., the fact that in studying the fundamental physical principles governing the strength and durability of a paint coating it is necessary to regard the coating as consisting of a series of flat arches, in which the pigment particles of largest characteristic size serve as the piers or supports for the flat arches of which the continuous film is composed. Corollary A--The strength and durability of a paint coating is determined by the strength and durability of the piers or supports (which consist of the characteristic pigment particles of the largest size). Corollary B--Owing to their inherent strength and durability the pigment particles of largest characteristic size which serve as supports for the paint coating should consist, in part at least, of chemically inert pigments, such as natural crystalline barium sulphate, calcium carbonate, magnesium silicate, etc.