_Alkyd resin._—Any condensation product involving a polybasic acid and a polyhydric alcohol. Typical examples are phthalic glyceride and its modifications containing combined fatty acids or rosin. Representative examples are Rezyls and Glyptal. _Aminoplast._—General terms for synthetic resins from amino or amido compounds. A typical example is urea-formaldehyde. _Amorphous._—Devoid of crystalline structure. This condition is rare. Many substances which are apparently amorphous show microcrystallinity, particularly under X-ray examination. _A-stage resins._—Thermosetting resins reacted only to the initial stage where they are soluble and fusible. The normal stage of a resin used for impregnation. _Bonding strength._—The amount of adhesion between a binder and filler. More specifically, the measure of the extent to which the composite layers of a laminated product are bonded together. _Brittleness._—Liability to break, generally to a conchoidal fracture. _B-stage resins._—Thermosetting resins reacted to a stage where they soften when heated and swell in contact with liquids but do not entirely fuse or dissolve. This is the preferred stage for the resin in molding compositions. _Casting._—Forming a material into a shape by pouring it when liquid into a mold. The product from the mold is used as such or mechanically worked in various ways to the final articles, as by sewing, cutting, blanking, turning, drilling, forming, swaging, grinding, polishing, sanding, or routing. _Compressive strength._—Resistance to deformation under applied pressure. _Condensation._—A chemical reaction in which two or more molecules combine with a separation of water or some other simple substance. Applied to synthetic resins it means the formation of a resin by combination of a number of molecules with elimination of water, ammonia, hydrogen chloride, or other simple substance. Examples of condensation resins are alkyd, phenol-aldehyde, and urea-formaldehyde resins. The final products are also called condensation-polymers. (See Polymerization.) _Copolymerization._—The term applied when two or more substances polymerize at the same time to yield a product which is not a mixture of separate polymers but a complex having properties different from either polymer alone. For example, vinylite is produced by polymerization of a mixture of vinyl acetate and vinyl chloride. _C-stage resins._—Thermosetting resins in the final stage in which they are infusible and insoluble. The state of the resin in the final molded article. _Curing._—The change of a binder from the soluble-fusible condition to the substantially insoluble-infusible form by chemical action. The heat-setting of a resinoid. Action is analogous to vulcanization of rubber. _Dielectric strength._—Voltage gradient at which a continuous electrical discharge will take place between two electrodes when the material in question is placed between the electrodes and a potential difference is applied to them.