While researching the true meaning of 50:50 solder, I came upon some information describing how to make different solder mixtures. Part of the article mentioned how a very small amount of zinc will "poison" the solder and goes on to explain how to remove the zinc by fluxing with sulfur.
Perhaps this has been brought up before but the information was new to me. There seem to be a good number of posters who have accidentally "poisoned" their wheel weight melts and if this helps clean up their alloy then I've done my good deed for the day.
Most relevant passages:
"From this it is clear that in making solder great care must be taken to exclude zinc from the pot. Zinc, lead, and tin do not alloy well, lead will unite with only 1.6 per cent of zinc, and above that proportion the metals are only mixed when melted, and on cooling partially separate.
Sufficient lead having been melted in the pot, about ˝ pound of lump sulphur, broken into pieces about the size of hickory nuts, is added, and the whole well stirred with a ladle, the sulphur unites with zinc and other impurities. The resultant sulphides are skimmed off in the form of a cake, more sulphur being added so long as sulphides continue to form. The bowl of the ladle, in the intervals of stirring, should be laid on the fire, to burn off any adherent sulphur. When sulphide ceases to be formed, a handful of resin is thrown into the pot, and the lead stirred. When the resin has burned, the lead is again skimmed, and a piece of tallow about the size of a hen's egg is put into the pot, the lead being again stirred and skimmed. In stirring the lead it is lifted up and poured back by the ladleful, a larger amount of lead being thus exposed to the action of the cleaning material."
&
"Zinc is the greatest trouble to the solder pot. Great care has to be taken to exclude it, or to get it out. It may get into the solder from a piece of zinc, having been put into the pot by mistake for lead, but more commonly brass, which is an alloy of copper and zinc, is the source of the zinc that poisons the pot, into which brass filings find their way whilst brass is being prepared for tinning. If the filing is done at the same bench as the wiping, splashes of metal may fall on the filings, which will adhere, and thus get into the pot. Solder that is poisoned by arsenic or antimony is beyond the plumber's skill to clean, but zinc can be extracted by stirring in powdered sulphur when the solder is in a semi-molten condition, and then melting the whole, when the combined sulphur and zinc will rise to the surface, and can be taken off in the form of a cake, the solder being left in good condition for use."
Link to the whole page : http://chestofbooks.com/home-improve...ke-Solder.html
Hope this helps some of you kind folks,
Hugh