Possible zinc contamination?

[machanic]

I'm new to casting boolits, was just prepping and test casting a new mold using a few (lead) fishing sinkers, I noticed when melting one sinker hadn't melted when the rest were compleatly melted but I was a little to late in scooping it out so I went ahead with casting, first few boolits came out frosty so I cooled lead and mold down a little, still frosty and I wasn't getting a complete fill of the cavity so I know the lead wasn't too hot, it was a small amount of lead (thankfully) so I finished casting. The boolits are very hard, they easly dent a prevous batch of boolits using wheel weights without themselves getting a mark on them. Is this what zinc contamination is like, I've read up on how it is the curse of casting and possible methods of removal but not much on the symptoms!!
Thanks for any help! machanic

[machanic]

The offensive boolits weigh in at 222.5gr mold is a Lee TL452-230-2R 230 gr

[lwknight]

That does not look like frosty or zinc to me.
It does look like a high antimony content with low or no tin.
I think your pot might have been a little cool believe it or not and that's the reason for partial casts. Also you might even have let the molds get too cool as well.

Solution would be to try adding some tin in a small experimental batch to see what happens and you might even try diluting the batch with that much again pure lead if its worth the trouble.

[machanic]

I diluted the fishing weights (presumably pure lead) with 1/5 by weight general purpose solder (presumably 50/50) to get a 10 pecent lead tin alloy, the solder although not labled as lead free could be a tin antimony alloy, how ugly should zinc contaminated castings look?

[lwknight]

There will be almost white gold smears in the melt if zinc is mixed in and if its very much there will be some silver oatmeal always floating.
I never actually cast zinconated bullets. I did purposely mix some zinc with lead and it was ugly.
It poured out fairly smooth and soft but within a few days , was so hard that it only broke and not bend.

[machanic]

Thanks L W Knight, the melt was smooth and shiny no silver oatmeal but required constant skimming (frosty oxides)

[lwknight]

OK now that I know about the 10 percent tin content that changes my whole way of thinking.
You should be able to cast at 540-560 degrees and cast fast enough to keep the molds hot.

[machanic]

I'll melt everything down tomorrow and try again! a little hotter.