Clear coat changed color/reflectance of paint

[MadGoat]

Check this out... this finished 4 year old paint job car just had the 1/4 panels and back half of the car sanded and re-cleared(only) due to a roof scratch and the silver paint now shows darker when in the shade in low light in this area than the original clear'd paint on the door and rest of car.

Anyone ever have this happen or know what would or could cause this?



But then get this... out in the sun, the re-cleared 1/4 panel and back end shows brighter and lighter, and the the door and front end appears darker. So odd.

This photo captures this disparity best. However in normal light/outside it is not truly as bad as the camera shows. But still not right. And I always say the camera does not lie. Or my eyes.

Then to check if it is a clear coat issue, the door shown was sanded and re-cleared the same way to see if it would give this darkening effect --- and it did NOT --- this is the photo. Only on the 1/4 and back half of the car that was re-cleared does it look like this.

By the way, whole car previously was down to bare metal when painted.

Can too much clear or the wrong clear do this? Any thoughts? I am no paint expert.


PPG reps are stumped.

[79 Camaro]

When I needed to have some paint repairs to my 71 C3 my body shop which is really good said additional layers of clear will with out a doubt will change the color compared to the panels next to it. So they had to re-spray the base coat and then do the clear.

[MadGoat]

I totally agree.... but the thing here is the door was then re-cleared to match exactly what was done on the back half and it did -not- change color/hue like the back half. So weird.

And the photo above was taken -after- the door was re-cleared ---- and the door shade to 1/4 difference is the same as it looked prior without the door being touched.

[dhutton]

Was it all cut and buffed the same way? Same grits and compounds?

Don

[MadGoat]

Yes sir.

Same can of clear and all. Same finishing materials and process etc.

Color was perfect prior to the clear being scuffed/sanded with 1000 grit for new clear.

While not ideal, the hope was then that the door being re-cleared would become like the 1/4 & back half and it did not. That is what has everyone scratching their heads.

[MadGoat]

Not as bad outside from door to 1/4 outdoors from the rear angle... but front end (not pictured) then shows darker in bright sunlight, while the re-cleared rear, that shows dark inside in the first pic posted, is whiter and brighter in sunlight than the front end.

Those big syllable words metamerism and reflectance are what I am told is happening by PPG.

But why, noone knows.

[dhutton]

There are some pretty bright folks over on the SPI forum. You could post over there.

Don

[thinkfastroth]

It might be that there was base material in the clear or from the time of the original paint job to the repair the paint manufacturer changed material formulas i.e. resin, pigment, pigment materials and what not. Did they use the same paint that was used during original paint job or did they have to remix the base?

[MadGoat]

The base was not repainted on the 1/4's. Only a small front of the roof area got color. Clear only the rest of the back half. I have been told something in the clear formula changed percentage wise from 40% to 43% but that should not affect the paint like it has -- otherwise no cars would be repaired properly today.

[thinkfastroth]

This might sound dumb but dose the deck lid match the quarters or the door?

[MadGoat]

Nothing dumb about your question.... but yes, the deck lid, and roof and 1/4's, all match each other both in the sun and out.

The whole back half just doesn't match with the doors and front end now.

Clear coat changed it all. But redoing the clear on the driver door did not change the driver door when done with an exact test on it. So thus in limbo right now.

[thinkfastroth]

OK so here is my thought there should be no reason to reclear the deck lid if just touching up the roof and this means the deck lid should match the doors provided every thing truly matched prier to touch up. This leaves me to believe that they actually used a blend coat over the entire back half of the car, it is very tricky to get silver to lay out when spraying and not get a form of modeling or striping. The other possibility is if the car was shot in pieces the paint laid out differentially and never truly matched to begin with.

[MadGoat]

Thanks.. paint was laid out perfectly prior. All shot at once. No issues. Until the roof got a scratch. Doh. The only color added was the front of the roof and base was fanned out a couple feet from there only. Perfect match by the way...

But being there is no break from the roof, the sail panels, 1/4's and trunk lid all got re-cleared to be uniform.

[thinkfastroth]

I have a sneaking hunch that a light coat of base made it on the entire back half in order to blend out possibly in the form of a mid coat thus changing color flop slightly.

[btmatt]

My guess is that the change in the clear formulation has changed the refractive index of the way light passes thru the clear. On darker colors it may not be noticeable, but silver reflects more light making it more presentable.

[MadGoat]

Thanks... great thoughts for sure. I would like to think and want to say a light base coat made it all the way around.. makes sense. But it did not.

And the change in clear formula or resin or whatever, even ever so slightly, surely could play a part. But then why did the new clear not cause the same darkening effect on the driver door? That is what is messed up and makes no sense.

[thinkfastroth]

Think of it like this if no new base material made it to the decklid than it should match the door not the quarters but if base material possibly made on to the decklid by accident through the clear then it would change the lay out and if there is enough material to change the deck lid the same goes for the quarters. Try taking off the deck lid and checking it against he door and se what happens.

[MadGoat]

Only the clear changed things on the entire back half of the car. The deck lid and 1/4's match the roof as one (again - only a small area of roof had base applied).

So clear changed everything there... but clear, when attempted on the door, did not darken it like the rear with the same amount of clear applied.

Thanks for the reply though.

[dhutton]

The issue is the interface between the new and old clear imho. The door is different because it was not sanded exactly the same as the quarter panel in terms of direction, pattern and depth.

This sort of thing is precisely why I am scared as heck to paint silver...

Don

[MadGoat]

The door is different because it was not sanded exactly the same as the quarter panel in terms of direction, pattern and depth.
Don

I can't say that is the case here... the 1/4 panel after being re-cleared the first time, was then re-sanded with the driver door and both had clear applied to see if it would then match. And it did not change the door hue as seen in the initial two tone pic.