Hi Towson,
Can help out here...................................
First up can you tell me and confirm what your factory Color code and color name is please?
1973 Mustangs were factory shot with what was known back then as an Acrylic Enamel. PPG called theirs Delstar. It was a two pack product (hardener added).This paint technology was also known as a single stage, mono enamel back then. As we know, the variety of colors came in solid colors and some metallic colors. Back in those days, base coat/ clear coat technology was not around, so our Mustangs were shot in mono acrylic enamels. For solid colors that was no big deal, but for metallic colors the metallic flakes were added to a clear /pigment/ binder mix. No separate clear coat top coats were applied.I used to spray mono enamels back in the mid Seventies just before the 2 pack clear coat/ base coat thing came in. Acrylic lacquers could of course be shot with a metallic base first, and then finished off with clean clear lacquer top coats.
So that said, one of the obvious ways to determine whether your car has factory paint, is to carry out a simple test. If your car is a factory metallic finish, all you need to do is get some non abrasive wax polish, a clean white cotton t shirt rag, and choose a few areas around the car panels, where you will apply the polish to small test patch areas. Now look at the polish rag. If it has turned to a dark dirty grey/black look, then you know straight away that the finish will be a mono enamel. This is because the metallic flakes are suspended in and throughout the entire thickness of the paint film, and when you polish the surface, you are exposing some of the metallic aluminum flakes on the top surface. It's the ali flakes that creates the dark color transfer to the white rag. Clean clear coats do not produce this effect when cut or polished - mono metallics do. Being a 2 pack paint, the mono enamels were very thinner resistant as well. You can test a very small area out of the way with a dab of thinners on a clean white rag. If it's the old mono paint or a modern day clear coat, then you won't get an immediate shedding reaction. If it's lacquer you will get an immediate shedding reaction on the rag.
Regards the use of micrometers to measure paint film thickness........................ It's a method i tend to avoid as trying to chase down and interperate accurate measurements can be tricky and not all that accurate. (see my link below to a really great article written on this very topic) In my case, my '73 Vert has most of the car in original factory Gold Glow metallic. I don't own a micro, and have never taken a reading of the thickness of the factory paint sorry. However, here are a few things to also help determine if you have had a respray or touch ups around your car. Examine each panel systematically around your car for gloss level evenness, and for orange peel evenness, and color variations regarding panel to panel matches and any noticible bad blending or fadeouts along the panels.Variations here will point to touch ups and/or a respray. Check for paint overspray on door rubbers, latches, screws and bolts that were not masked up properly.
Check for stone chips around the car, especially around the lower areas which are prone to gravel rash/chipping. Check for any paint scratches, nicks, small impact dents, paint runs, paint worn away proud edges, paint cut throughs. If your car is factory original paint, then you will have those issues around your car to some degree or another. Other signs include masking tape paint edges in the inner panels like door jambs, dry spray in the inner panel from over spray creep in, color/ finish variations in the inner sections compared to the outside. Get a powerfull small magnet and place it on the surface panels around your car. If it falls off the panel, you've more than likely got bondo/ refinish issues. And the list goes on. ( see my link below for another super good article on this very topic)
Lastly here is a link to a slightly off topic interesting article regarding the value of original paint finishes on classic cars.
Link 1. Micrometer readings...............................................
https://newoldcars.com/what-a-paint-thickness-gauge-really-tells-you/
Link 2. How to verify original paint ......................................
https://newoldcars.com/how-to-spot-a-repaint/
Link 3. The value of original paint .......................................
https://newoldcars.com/the-true-value-of-original-paint/
Hope all that helps,
Greg. (pro painter)
