Using Invisible Light Photography to Evaluate Paints for Vehicular Use

[OlDoinyo]

A few days ago, my son approached me with a request: he wants to repaint a classic vehicle, and he has chosen some candidate paint colors, but he wished to know the UV and IR reflectance properties of these paints as well as what the eye sees. Where we live, the summers are long and hot, so colors that are dark, especially dark in the IR, tend to turn a vehicle into a solar oven--not good. I myself am partial to white for similar reasons. UV, being only 5% of the solar budget, has much less impact on heating, but one could perhaps conclude something about fade resistance from the UV image.

 

So the paint samples were sprayed and photographed. The objects at the bottom are some things I tossed in as reference surfaces.

 

 

As it turned out, only three of the samples displayed any IR absorbance at all, and those were varying degrees of faint. The blue sample is the palest in UV, so might be potentially the most fade-resistant. But this is conjecture at this point. A decision has yet to be made as of this writing.

[bvf]

Hos did you get that red-brown colour out of the Baader? How did you WB?

 

That colour is what I would expect to get for oil-based paints using Tri-colour UV, but I've never seen a colour like that from the Baader U.

[Stefano]

He probably swapped the channels, doing a BGR representation. BGR images are somewhat similar to tri-color images, both in UV and IR, even if the amount of color information is significantly lower (you have basically two colors instead of three).

[dabateman]

Top left right white looks to be a winner. Lowish in UV and white in other wavelengths. Had never thought to test this.

Now I wonder what my white car looks like.

[Stefano]

My dad's car is very non-uniform in UV. It has UV-blue spots randomly on the entire surface, and the background is UV-gray. It looks uniformly gray in visible light.

[Andy Perrin]

He’s the only one on the board who routinely does BGR for UV photos, but he’s been doing it for years, so we’re used to it. I confess that I usually swap them back because the swapped colors are almost invisible to my eyes.

[Stefano]

I sometimes like BGR photos, they look more natural to me, probably because they are more similar to an actual tri-color image. In particular, I like the blue skies it gives. But I am too used to the standard blue/violet/yellow palette, and I like it.

[dabateman]

My dad's car is very non-uniform in UV. It has UV-blue spots randomly on the entire surface, and the background is UV-gray. It looks uniformly gray in visible light.

 

That most likely is touch up paint, where it was scratched or chipped. Most likely not manufacturers original blend. If bought used, people will use nail polish here as touch up as in visible sun light its hard to see the difference. But it will come out in fluorescent light of a parking garage.

[bvf]

My dad's car is very non-uniform in UV. It has UV-blue spots randomly on the entire surface, and the background is UV-gray. It looks uniformly gray in visible light.

That most likely is touch up paint, where it was scratched or chipped. Most likely not manufacturers original blend. If bought used, people will use nail polish here as touch up as in visible sun light its hard to see the difference. But it will come out in fluorescent light of a parking garage.

 

As with Stephan's UV image of repairs in a church, I wasn't aware of this aspect of UV photography. But looking at the Baader web site on the Baader U it says "Non-astronomical applications possible: e.g. check for paint damage on cars"

[Stefano]

Here there are a few examples: https://youtu.be/KFZRNHzqZLM

[bvf]

Here there are a few examples: https://youtu.be/KFZRNHzqZLM

 

Aha - another Steinheil fan! In this case the Cassarit. Also a Shinker enlarger lens - which I'd never heard of before, although there are some Shinker lenses on ebay. And an El-Nik, but can't see which one.

[Andy Perrin]

As with Stephan's UV image of repairs in a church, I wasn't aware of this aspect of UV photography. But looking at the Baader web site on the Baader U it says "Non-astronomical applications possible: e.g. check for paint damage on cars"

Yeah, saw some interesting paint differences here:

https://www.ultravioletphotography.com/content/index.php/topic/1863-buzzards-bay-wareham-massachusetts/page__view__findpost__p__12830

and here:

https://www.ultravioletphotography.com/content/index.php/topic/3260-omega-340bp10-excite-fura-20mm-filter/page__view__findpost__p__27337

[Stefano]

You can really see the invisible with UV photography (and IR photography too, but to a lesser degree). This is (also) why I love it.

[bvf]

Yeah, saw some interesting paint differences here:

https://www.ultravio...dpost__p__12830

and here:

https://www.ultravio...dpost__p__27337

 

In the first link, this is what I've seen regularly - it is the difference between oil-based paint (blue/purple) and water-based paints. (In tri-colour UV the oil-based paints - and plastics - come out brown, irrespective of the visible colour.)

 

It's the car-paint differences - as in the second link - that is new to me.