Just put some Sig clear dope from an old can on an all all sheet FF Dakota.  A day or so later the finish looked like I had used a dirty brush with black dope left in it.  It looked fine when it was wet.  Any ideas why it turned?  Rust maybe?
Thx,
Mel D.

Both butyrate & nitrate dopes will turn to an amber shade if they are quite old, have been exposed to air quite a bit, have been stored in high ambient temperatures (over about 95 degrees F), and/or have begun reacting with the container material.  Turning to an amber shade is the result of the dope becoming acidic; however, I have never encountered any dope product turning black - beats me (and I have some butyrate dope that is 20+ years old that I still use)!