<Li> Metallic paints contain aluminium flakes to create a sparkling and grainy effect, generally referred to as a metallic look . This paint is harder to manage than solid paints because of the extra dimensions to consider . Metallic and pearlescent paints must be applied evenly to ensure a consistent looking finish without light and dark spots which are often called "mottling". Metallic basecoats are formulated so that the aluminium flake is parallel to the substrate . This maximises the "flop". This is the difference in the brightness between looking perpendicularly at the paint and that at an acute angle . The "flop" is maximised if the basecoat increases in viscosity shortly after application so that the aluminium flake which is in a random orientation after spraying is locked into this position while there is still much solvent (or water) in the coating . Subsequent evaporation of the solvent (or water), leads to a reduction in the film thickness of the drying coating, causing the aluminium flake to be dragged into an orientation parallel to the substrate . This orientation then needs to be unaffected by the application of the clear coat solvents . The formulation of the clear coat needs to be carefully chosen so that it will not "re-dissolve" the basecoat and thus affect the orientation of the metallic flake but will still exhibit enough adhesion between the coatings so as to avoid delamination of the clear coat . A similar mode of action occurs with pearlescent pigmented basecoats . </Li> <Li> Pearlescent Paints contain special iridescent pigments commonly referred to as "pearls". Pearl pigments impart a colored sparkle to the finish which works to create depth of color . Pearlescent paints can be two stage in nature (pearl base color + clear) or 3 stage in nature (basecoat + pearl mid-coat + clear - coat). </Li> <P> Usually sprayed on top of a colored basecoat, clearcoat is a glossy and transparent coating that forms the final interface with the environment . For this reason, clearcoat must be durable enough to resist abrasion and chemically stable enough to withstand UV light . Clearcoat can be either solvent or water - borne . </P> <P> One part and two part formulations are often referred to as 1k and 2k respectively . OEM (original equipment manufacture) clear coats applied to the metal bodies of cars are normally 1K systems since they can be heated to around 140 deg C to effect cure . The clear coats applied to the plastic components like the bumpers and wing mirrors however are 2K systems since they can normally only accept temperatures up to about 90 deg C. These 2 K systems are normally applied "off line" with the coated plastic parts fixed to the painted metallic body . Owing to the difference in formulation of the 1K and 2K systems and the fact they are coated in different locations they have a different effect on the "redissolving" of the metallic base coat . This is most easily seen in the light metallic paints like the silver and light blue or green shades where the "flop" difference is most marked . </P>

When was metallic paint first used on cars