[Heathkit] What is this black stuff?

[K4BEV at aol.com]

As I've previously stated:
I have obtained a HW-9 that *never worked*.
 
The soldering job on it was pathetic, so I've been touching it up, clearing 
bridges, etc.
 
Some (not all) of the joints with an overly generous amount of solder are a 
bit scary.
When heated a black goo boils out of them. This stuff immediatly fouls my 
iron's tip.
But it cleans right off of the iron.
 
I've carefully inspected the pad and wires where this stuff was and am not 
finding any corrosion... I thought it might be acid core flux that I'm seeing, 
but I just don't know..
 
Any idea what I'm looking at? Cause for concern, or just some strange solder??
 
73, Don - K4BEV



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