How to tell if lead is contaminated with Zinc?

[greenjoytj]

I was casting Tuesday & Wednesday with 4 new pieces of casting equipment so I didn’t have high hopes for success this time.
1) New furnace, a RCBS ProMelt-2
2) New mold, SAECO #955 4 cavity 255 grain for 45 Colt.
3) New single element hot plate, to preheat & keep the heavy iron mold hot.
4) Alloy metal - mystery metal of unknown lead composition.

The problems I encountered in casting and with the cooled bullets:
1) Of the thousand bullets cast all show frosted except for the wide base drive band it’s mostly shinny.
2) A large percentage cast with a slightly rounded base edge.

How would I be able to tell if the mystery alloy was contaminated with zinc?

The new furnace was much slower to melt the lead than my old LEE Pro 20#. The Pro Melt-2 is 25# pot. That’s a 25 percent increase in metal weight to heat and melt.

This casting session was the first time I’ve use a hot plate to preheat a mold. I put a 4”x8” thin 1/16” thick sheet of steel over the burner coil tube a heat spreader and ran the hot plate at a low #3 heat setting.

I use a LEE lead hardness tester on all the 6 one pound ingots cast from the last inch of lead from the bottom of the furnace pot. BHN 8 is as low as the LEE reference chart goes and my measurements show the alloy is BHN 8 to estimated 7.8

I was lowering the pot temp from a high 845* because at the high temp I couldn’t keep a sprue puddle on the cutter plate it rolled off like water.

At ~720* I could keep a Lima bean sized puddle on each inlet hole, the puddle was usually connected to the next in one finger length strip.

A random sample of as cast bullets averaged weight is 263.1 grains and diameter is .4559” to .4564”

Next time I’ll try to cast at hotter temp to get more diameter shrinkage and lighter weight and use a known alloy instead of scrap.

[RED BEAR]

they tell me pour a little muriatic acid on them and if there is zinc it will fizz. if not nothing. i wouldn't use them without washing off acid. all i have ever used is coww and scrap.

[sutherpride59]

I’m not sure how you would be getting frosting with such a low BHN being as the frosting come from the antimony. Either way frosting is a hot mold not a hot melt, I would turn the heat up to 800 and try again, also adding 2% Tin and make sure you have your spue plate a little loos so the base can get proper venting.

[toallmy]

That's not very hard alloy to have Zink in it .

[454PB]

Those symptoms could also be from a contaminated mould. Was it thoroughly degreased before use?

[Taterhead]

454 is probably nosing at the culprit.

[greenjoytj]

I used a sprayed can of brake cleaner to clean the mold, I don’t know how to get it the mold any more clean or de-oiled.
I’m getting lead sticking to the top of the mold even though I was lubing the mold top with a PAG 100 refrigerant lubricant ( just bought some Red Line 2-stroke full synthetic ester racing oil) applied with a Q-tip applicator. Now it’s been wiped with a heavy coat of KROIL to see if the lead smears will pop off if the oil can migrate underneath the lead.
I was thinking if I had zinc contamination the bullets would be lighter than the 263grs I’m weighing.
I suspect there is little to no tin in this alloy I suspect all the hardness is from antimony.
I have some Rotometal 20:1 to test this mold on the next casting session.
This SAECO 955 mold has a massive chunk of solid iron between the bullet nose and the mold base, it so big SAECO could have flipped it over and cut 2 more cavities between the alignment pins.
The sprue cutter will swing open & close freely when the mold is cold but there is no up an down play between sprue cutter and the top of the mold block.

[lightman]

It does not sound like zinc but you could do the acid test to check. It could be a contaminated mold. Did you spray it and scrub it with a tooth brush and spray it again? My strongest suggestion is to increase the flow filling the mold. Your pot temperature of 720-730º should be about right but you should be able to form a full size sprue.

[sutherpride59]

I say take it to the extreme then back it down, kind of a proof of concept. Scrub the mold with hot water and dawn dish soap the blue kind 3 times, smoke the mold with a bic lighter or a match no candles, then turn the pot to full blast, put your mold on the stove top or hot plate to preheat, pour your melt as fast as you can, check your sprue plate for burrs. If it still doesn’t make good bullets then it’s time to try a new batch of lead. If you get good bullets you can back the heat off and figure out what heat you need your melt at to get good results. If you still need help you can PM me for my phone number and I can help you out. I’m not an expert but I bet we could figure it out.

[Joe S]

I believe zinc contaminated lead will have a strange looking bluish color on the surface which you cannot get rid of, no matter how much you try to skim it off.
The main thing about Zinc is it increases the surface tension of the lead so that you absolutely cannot make high quality bullets with it. The mold will NOT fill out.

In your case, the frosting should not be a concern, it has no relation to zinc. It is probably caused by your lead temperature being too high. Frosted bullets are OK to shoot, as far as I know.
If the bullets have rounded bases, try a different pouring technique. Each mold has its own preferences. Perhaps you need to keep the ladle in contact with the mold for a little longer, ( if you are "pressure casting " with a ladle).
If you do have zinc contamination, take the lead to a scrap metal dealer and get what you can for it, use a wire brush to clean out the pot, and clean the mold.

I believe there was a thread on the ASSRA forum about a shooter who used brake cleaner and suffered severe permanent lung injury due to the fumes.
I clean my molds with Acetone, MET, or denatured alcohol, all of which are highly volatile and dangerous to breath, so I always do it outside. The brake cleaner produced poison gas which caused the injury, so I avoid brake cleaner.
I hope this helps.
Joe S

[Tom W.]

IIRC zinc will make your alloy look like oatmeal.

[mdi]

I'm no expert but your symptoms seem to be from temperature control. I don't think I'd go much over 700 degrees with the melt, and with that soft alloy prolly closer to 600-650 degrees. Frosty surfaces is usually from too high temp, but rounded edges is from too cool. A couple thoughts; Warm the mold a little longer, sprue plate down, lower the melt temp and add some tin for fill out. Unless you have a specific reason for that soft alloy, more tin and/or mix with a known alloy, mebbe a little Lyman #2 or linotype would help. It wouldn't hurt to try a new mold with a known alloy, from a reliable source, to start..

I've only encountered zinc once, and the melt looked a bit like oatmeal (I believe zinc melts at a higher temp., around 780 degrees, than lead so another reason to lower the melt temp.).

[Outpost75]

"Dilution is the Solution to Pollution."

Use a thermometer.

Keep melt temperature well below 750 degs. F, measured with a thermometer.

This is below the melting point of Zn and you can flux pot and skim off great majority of the "oatmeal."

If alloy still casts with "orange peel" texture on bullets, dilute it by equal parts of known uncontaminated alloy and continue.

[Grmps]

this could be a ventilation problem.

when I have a mold problem, the first thing I do is clean the mold again as well as I can (I use dawn soap and water, I feel brake cleaner leaves a residue. when I do use brake cleaner, I rinse with starting fluid before I blow the cavities out.

IF the second cleaning AND a known alloy doesn't work, get a diamond hone or a fine sharpening stone and lightly ease the top inside edges of the mold to help ventilation under the sprue plate. (look at the existing vent line for a size comparisson.

[toallmy]

Grmps that little break of the inter edge of the top if the mold has helped me quite a bit with venting problems .

[Neverhome]

Maybe clean the mold thoroughly to get rid of ALL lube. Try a bunch of pours with out adding lube. A handful won't destroy your mold. I've had bad base fillout from too much sprue lube. Try it dry. If it doesn't get better no harm no foul. If it does then fine tune your lube application.

And yes muriatic acid/hydrochloric acid will show zinc contamination readily. Available at most hardware stores. Good for peace of mind as you could chase your tail endlessly

[Joe S]

I am not a chemist but I believe I read on the ASSRA forum that testing for zinc with muriatic or hydrochloric acid produces toxic fumes, so check it out and take necessary precautions before you proceed. Joe S

[Neverhome]

Zinc and hydrochloric acid offgasses Hydrogen. It's safe and particularly so because of how little is required for the test

[pls1911]

With apology to Jeff Foxworthy's "might be a redneck" lines...


If the sketchy pour looks like the Tin Man's soft stool diarrhea, You might have zinc in your alloy
If the pot melt wears a complexion like an asphalt road, You might have zinc in your alloy
If you can't flux enough to make any of the above better, You might have zinc in your alloy
If your wheel weight snaps like a brittle pencil, You might have zinc in your alloy
If a broken wheel weight end fizz in acid, You might have zinc in your alloy
If you run your pot to 900*, overheat your mold, and still have poor fill out, You might have zinc in your alloy
If you used lead shavings from industrial dies, and experience all the above, You absolutely have zinc and other mystery metal) in your alloy.