I have a confession to make

[Soylent]

See Trev, you should have put your pickguard on the roof in the sun instead of in that coffee/coke mixture.. what ever were you thinking.  :laughing7:

 

[jalane]

I just can't imagine it being as simple as the strings protecting from dirt in the sense that if I threw a handful of dirt at the guitar, that part would get less dirty. but, when you think about which part of the pickguard would get lots of sweat, hand juice, etc. . . . it would be everything minus that under the strings. (assuming you kept the guitar stringed up.) Also, most folks don't exactly clean/dust that part of the pickguard every day, so mebe dust and (yuck) skin flakes somewhat protect that part just a slight bit more over a really long period of time (from the sun?) IDK. Just some guesses on how it might actually happen. Obviously if they do it to relics, there must be some vintage instruments that this happened to. and if it happened, there must be an explanation for how it happened.

Well, imho, most relic jobs overdo the difference in coloration on the pickguard.  The difference is usually not as robust as it is on the two guitars pictured in this thread. 

Another reason this occurs naturally, though, is that parts of the pickguard outside the string area get scratched and scuffed up from your guitar pick, finger oil, etc, while the area under the strings is mostly protected from that stuff.  As it gets scuffed i'm pretty sure it becomes less resistant to coloration from sunlight, smoke, etc.  When i soaked some plastic parts in coffee, tea, and cigarette butts awhile back they didn't really change color at all until i scuffed them up with sandpaper. 

 

[B3Guy]

yeah, the scuffing theory actually makes some sense. dirt and stuff probably rubs into and stays in the scuffed part a lot easier.