Symptoms of zinc contamination?

[35 Whelen]

A few days ago I smelted about 60 lbs. of WW's. I've read much about of zinc contamination, but figured it was more of an internet "ghost" than a reality. I know the zinc weights exist, but I've never had a problem with them. But, just to be safe, I smelt at around 700° F (Zinc melts at something over 780° F) according to my Craftsman digital meter.
Anyhow, I smelted as usual, monitoring the temp and poured the cleaned WW's into ingots. A few days later, I began casting bullets for the local High Power match. I always flux again after the metal is melted in my pot. I use candle wax and stir the mix with pine door shims. When I scraped the gunk off the top, I got a blob of grey stuff off.
I first used my NOE K-31 180 mould. I didn't examine any bullets closely, and didn't see any problems. Next I grabbed my Lyman 311672 after heating it on top of the pot, I began casting giving the bullets a look at as they dropped from the mould. I immediately began noticing fill-out problems in the area of the lube grooves. I stopped and cleaned out the vent lines. Things seemed better, so I continued casting until the pot was almost empty. I decided to visually sort some of the bullets and began find voids again in the are of the lube grooves. Ultimately, I had probably a 50% rejection rate. This mould NEVER gives me problems and casts very, very accurate bullets.
Later I refilled the pot and cast with a tried and true 311291 single cavity mould. This mould too is very reliable and never gives me problems. But again, i found voids in the bullets. This time almost everywhere.
Does this sound like zinc? FWIW I run my SAECO pot very hot...maxed out in fact as that's always worked best for me.

35W

[docone31]

Zinc will look like dark spots on the castings.
Your spout will slow down if the heat was not enough.
I use zinc in my castings, so I cast hot. If there is too much zinc, I add some pure to "sweeten it, in other words thin the melt.
I like zinc. I like to shoot paper, and hardness does not hurt me.

[wistlepig1]

I don't know if this will help but in april I had collected some Zn WW and desided to melt them into door stops. With a good propane tourch I had a heck of a time melting them and I had to apply the heat for a long period of time just to melt them. Without a lot of heat over a long period I think Zn is unlikely but I sure am NO expert in this area. There are others here that can give you better info than my one time experiment.

[RP]

IF you think you got zinc try the M-acid test. I have tried it and its a easy test. I also used the sulfur to remove zinc from lead that was more exicting but worked.

[DLCTEX]

I have cast a lot with some zinc in the mix and experienced no fillout problems. If you aren't getting an "oatmeal" slush appearance when first melted then I don't think the problem is zinc. Also my boolits with zinc have a whiter look than regular ww boolits, like sterling silver where it isn't polished. Zinc will also clog the spout on a bottom pour quickly due to the spout being cooler than the pot and zinc having a higher melt temp.

[madsenshooter]

I thought I had some zinc or cadmium not long ago 35W. Funny I was working with the NOE K31 too. Couldn't get them to cast, but I could get an iron mold to cast. Turned out that I just wasn't getting the melt hot enough. My little Lee pot needed a new element, so double check the temp of your melter first. Maxed out, may not be what it used to be.