Hmmmm... Zinc in smelt. Always a frustrating situation..... But....
Roosters link above..(see below) is a discussion of this issue. Think I am even in there a few times.
http://castboolits.gunloads.com/showthread.php?t=63082
You will read some neat things. Acid, Sulfur, Borax. All can do good things to a 'messed' up smelt. I have a 'few' ingots in my 'stable' that are bad news when casted. And I hate to 'toss' any, ingot after spending the time and effort make them. But,,,some are BAD..... So what to do?
My first question is, 'have you casted' from any of the bad new Bears ingots? How did they do? Do 'you' like them?
Or, simply...in YOUR opinion...'how good is 'good'? What are you using the boolits for? Beer Can destruction? Target Competition?
I have casted some pretty 'skimpy' boolits in my day. Sized them, lubed them. loaded them. Shot them. Had fun all the way through.
And, have made some pretty nifty boolits too. (if I don't say so myself)..[and I do]... these boolits too offered fun, enjoyment and relaxation during my efforts.
The bad ones you show, don't, to me, look too bad to toss. And, in the link provided you can read how to clean them up. I have fluxed with sawdust and sulfur many,many, times. It is always my basic flux in my smelt pot. Sulfur is available from the nursery. Read the posts I provided here today and you can find where to get 'free' sawdust. I say, get the ingots in question, with some sawdust and sulfur and wax, and resmelt the lot. Flux with sawdust/sulfur three or four times, then the wax as a finish. Pour them out and see what happens. I've 'saved' some pretty 'iffy' ingots with sawdust, sulfur, wax and borax. Learned in the process.
Again, your use and your need is the driver here. Hunting and target use...??? Cast the 'good ingots'. Milk jugs, beer cans...the lesser ingots.
And...If you add 'chemicals' to your smelt pot...STAY SAFE with that stuff. ACID FUMES can blind you. Face shield, leather gloves, sleeves, apron, leather boots. Remember...'it ain't fun if your hurtin'..... And, if your fluxing with this stuff...ALWAYS...ALWAYS...OUTSIDE....and up wind.
Good Luck.
Nose Dive.
Cheap, Fast, Good. Kindly pick two.
PS: here is a good spot to do some reading too. ND
http://www.lasc.us/CastBulletNotes.htm