Why did Fat Man have dark paint markings?

You asked a terrific question about the black paint on Fat Man's protruding parts. Fat Man was delivered to Tinian Island in parts and assembled on the island. The implosion design had been tested in New Mexico, but had never been exposed to the kind of humidity it experienced in the Pacific. After assembly, but before loading it onto the bomber Bock's Car,  all of Fat man's seams were sprayed with a sealer. I think it was asphaltum or something similar. Many of the protruding parts were bolted on, so their seams were included in the treatment.

Was Flouride a by-product of the Manhattan Project?

 I love this question which I found this morning in our question box. So much in fact that I just had to share it with a Lab chemist I know. (Because I had no idea.) I have copied his response in full here. I recommend both of the links. Thank you for providing me with this opportunity to learn!

"I’m guessing that they are referring to the de-conversion of uranium hexafluoride to form uranium metal.  A byproduct of the de-conversion process would be fluorine – typically as a fluoride.

Here is a NRC web page providing some information on uranium de-conversion:

http://www.nrc.gov/materials/fuel-cycle-fac/ur-deconversion.html

Also web page for the company that is building a facility in southern New Mexico for uranium de-conversion:

http://www.intisoid.com/index.php/fep/more-information/1300-2/

For example the above facility apparently plans to produce the SiF4 (silicon hexafluoride) as the byproduct instead of a fluoride salt.  As mentioned SiF4 is typically used to make high purity silicon for electronic applications.

With regard to Manhattan Project I’m not sure where the de-conversion process took place and what form, e.g. fluoride salt, they produced at the time."

Are the Little Boy and Fat Man models at the BSM full scale?

Our replicas are full scale. Actually around 2005 ago we replaced our original models with two even better replicas that are more accurate in representing the appearances of the two weapons.  The two new versions, constructed of steel and fiber glass are actually ballasted with concrete to represent the actual weights of the original weapons. Not that we ever heft them.