I don't recall saying something about the bumpers not being primed; read properly before commenting. This is common knowledge.
I said
"Due to costs, usually no manufacturer (except high cost cars or special orders) applies a lighter pre-layer of paint to offer a lighter base for the final paint".
So I was referring to a layer of paint not primer.
Try your friend Google and search for images "oem primed bumper for sale" and see what color are they. They are black.
The primer applied is in general transparent for two reasons:
- transparent has the least influence on any color
and that leads to
- the bumpers need to be ready for any color when the manufacturer decides what colors he wants
Priming Plastics
P572-2001 Adhesion Primer for Plastics is fast, transparent, suitable for use on all paintable plastic substrates** and helps avoid the need to identify the substrate before spraying.
P572-212 Primer for PP and PE is a low build, ready-for-use transparent primer for use over PE*, PP and PP/EPDM.
P572-173 Primer is a flexible, pigmented primer for use over PUR, PC, PA, Pocan (PBT), ABS, PPO and flexible PVC.These two primers can be mixed together to form a two-component system for use when the plastic substrate is unknown.
http://www.ppg.com/coatings/nexaauto...nPlastics.aspx
They can mix pigmented primer for an ulterior paint but no manufacturer will spend that money on bumpers.
The first layer applied on the bumper it looks different for few reasons:
* The plastic dissipates heat more slowly than metal and drying time is an important factor in appearance. Paint dries more slowly so the chemicals have more time to evaporate and metal flakes have more time to settle, resulting in a different appearance.
* Plastic holds more static electricity than metal and that can cause metal flakes to align different than on a metal surface.
* Paint is much better than in the past, however, the black main color of the bumper still influences the color (especially on lighter colors, opposite to black) if only layer of paint is applied.
For better results you need to apply a second layer of paint; that will eliminate the flake orientation problem and the color will be more consistent eliminating the influence of the black plastic. However, between the two layers we need a drying process so the flakes will set properly this time over the first layer. Two layers applied one after another without a drying step in between will do nothing in terms of flake orientation.
The bumpers will look perfect if two layers of paint are applied, but no manufacturer will spend double time and money when they can paint two bumpers with the same budget.
Nonetheless, look at any new car, due to the first layer applied on black plastic, the bumpers are usually darker than the car.
Where people come up with stuff like this?
Some of us painted some cars in the past and had the chance to visit some very exquisite car factories.