n When a product is synthesized from a reaction involving two or more raw materials, it may be said to be internally plasticized if one of the raw materials is able to confer plasticity or flexibility to it. In other words, the product is plasticized because it is build up from a component which is naturally plastic. For example, an oil-modified alkyd, in which phthalic anhydride and glycerol are combined with drying oil fatty acids, is internally plasticized by reason of the presence of the fatty acid component. If a congo varnish were made by interaction of run congo and linseed oil monoglyceride, it could be described as internally plasticized, in contrast to a varnish made by simple dissolution of run congo in linseed oil, which would be externally plasticized. Also a polyvinyl acetate-acrylic copolymer is internally plasticized while a polyvinyl acetate homopolymer, into which a plasticizer has been stirred, is externally plasticized. See  Internal Plasticizer.