I just opened a set of PE parts and noticed these weird brown scorch mark like spots.


I was wondering if anyone happened to know:
A. what these spots are exactly?
B. if they are of any danger to the model (in the sense of the paint not sticking well or the parts becoming very brittle)?

The parts are made by chemical milling of the metal. That is residue from the acids and cleaners used in the process. It probably is not a problem now but if you are concerned try going over it with a fine abrasive.

KL

Oxidation? Did you try rubbing with steel wool, or fine sandpaper?

As mentioned above, PE is made using a chemical "milling" (etching) process. The discolorations on PE sets are typically either residue left behind from incomplete post-etching neutralization and cleaning processes, or tarnishing and surface oxidation - which may result from pre-packaging handling, etc.

Unless the "blem" is an oil, it is unlikely to affect either part stability and longevity in your build (i.e., it won't corrode away) or affect your painting.

To be safe, I always inspect PE sets and wash them in soap water with attention to the blems. Washing will remove oils left from processing and handling and generally remove any possible acid residues left from etching. If the blem has some marked surface texture that you don't want coming through your paint... do a light sanding with very fine grit paper to smooth and burnish the PE sheet before cutting parts off.

Cheers! Bob

Thanks for the help all, I've taken to it with a sanding stick and that seems to have done the job and the spots are gone

looks like some type of contamination before the etching process. They may not have cleaned the brass completely before hand. As stated above fine sand paper or sanding stick.If can soak the pe fret in lacquer thinner or denatured alcohol after your done it should get rid of what ever contaminated the fret. Just to make sure your paint will adhere properly.