brugnospamsia wrote:

I found the wazy "La-co" flux to be the most reliable - I even managed to
solder copper to lead once or twice.

I'd always used fluxite (a habit inherited from dad who worked for the
gas board) and was doing som eplumbing for a friend last weekend, I was
running low on flux so switched to an old tin of the La-Co you
mentioned, I thought it was more like vaseline than flux, but was very
surprised at the better "wetting" it achieved, it positively drags the
solder out to form a nice bright ring on the joint ...