Strange color and crust What's going on?

[lksmith]

Hey ya'll!
I decided to get some 40:1 from Rotometals do I could cast soft boolits and still have good fill out.
Since I had melted WW and roof lead in my pot and gotten a crust that just didn't look right, i got the wire wheel and cleaned up the pot and got it nice and clean (at least looked clean) and put the ingot in after a few minutes on high it melted but I remembered that I hadn't heated my mold. so I sat the mold across the top of the pot (2-3" above the lead) to pre-heat.
I got back and had a orange-yellowish crust on top that was pretty ugly looking that I had to keep skimming off, adn can't for the life of me figure out what it is. Any ideas?

The pot is a Lee bottom pour, dial was set on 10. Had 1 ingot (5#)
Mold Mihec 452-200HP

Did get some purty boolits though.

[Defcon-One]

You're pot is Way too hot! Buy a thermometer/pyrometer!

You're basically using pure lead with a bit of Tin, about 2.4% Sn. At temps over 800 degrees F you will get funny colors like blue, purple, gold, etc. and crusty yellowish stuff on the sides of your pot.

My Lee 10 lb. pot works best around 7-7.5 on the dial. At 10 it will almost boil Lead. (OK, just kidding, but at 10 it will melt Zinc every time and fast.)

[Freightman]

You skimmed off the tin

[lksmith]

You skimmed off the tin

I had first thought that but the fill out I am getting is much better than pure lead

[cbrick]

You're pot is Way Too Hot! Buy a thermometer.

Never run a Pb/Sn alloy hotter than about 725. Tin oxidizes very rapidly past 750 degrees and cannot do what it is in the alloy to do. What you are trying to skim off is your tin.

Rick

[lksmith]

You're pot is Way Too Hot! Buy a thermometer.

Never run a Pb/Sn alloy hotter than about 725. Tin oxidizes very rapidly past 750 degrees and cannot do what it is in the alloy to do. What you are trying to skim off is your tin.

Rick

is there a way to flux it back in?

[cbrick]

is there a way to flux it back in?

Yes there is. Read chapter 4, I suggest reading the entire book but chapter 4 is on what flux is, what you want it to do and how it does it.

From Ingot To Target (http://www.lasc.us/Fryxell_Book_textonly2.pdf)

Rick

[Linstrum]

Like has been said, check your temperature! I run between 700ºF and 900ºF depending on the particular alloy. High temperature hastens the oxidation and potential loss of both tin and antimony. I use a set of Temple Sticks to check temperature, they are very fast and accurate enough to verify temperature when I can't get a thermocouple tip where it can pick up heat to take a temperature reading. An infrared reading thermometer is the best but I don't know what a long-lasting reliable one costs nowadays. If you are getting orange colored dross in only one particular batch of alloy, it is time to take a look at the alloy. I know you said the metal came from Rotometal, but suppliers aren't perfect and they can mess up orders or get the wrong stuff in a batch of alloy like anyone else. Red lead oxide is a red-orange to orange colored powder, but it only forms at high heat unless a lot of some kind of powerful oxidizer like potassium nitrate somehow gets into the molten alloy. See:

http://en.wikipedia.org/wiki/Red_lead

Tin oxide is white when pure but is gray or black when it forms out of a lead alloy. I guess it is possible for an electric melter to get red hot so red lead can form, but your melting furnace life will be pretty short. Other common things that make orange powdery dross are the metals antimony, cadmium, bismuth, and zinc that are all used in common low melting point alloys that look like lead. They all have orangish to yellow oxides when hot. Zinc oxide is interesting because when pure it is bright canary yellow just below red heat but turns white when it cools down and can be used to indicate temperature, but the other oxides don't change color like that. If the orange color vanishes when it cools down, then you may have zinc present.

Read up on "fluxes". The material used to get tin back into solution in the alloy is actually a reducing agent and not a flux. Fluxes and reducing agents have totally different functions but unfortunately in the casting community the terms are commonly confused and misused. Things like wax, sugar, sawdust, charcoal, pine pitch, plastic sandwich baggies, etc., can all be used as highly effective reducing agents. Pine rosin and pitch work well as both fluxes and reducing agents.

Good luck!

rl 1,190

[TenTea]

My first ingot melt of what was billed as *pure lead* had some skim exactly as described.
I put it back into the cold pot afterward and will try to *reduce* it back in with beeswax next melt and see if I can get it into the mix again.

[Linstrum]

By the way, a quick and easy rule of thumb is if you can see a faint red heat in a room that is dark enough to make reading difficult, the temperature is over 900ºF. You don't need a thermometer for that.

rl 1,191

[runfiverun]

yellow orange is classic lead oxide.
I used to work with lead oxide making electro ceramics from it.
it was always orange colored with a yellow tint to it, tin oxide was grey.

[lksmith]

When it cools off it leaves a yellow residue on the pot but the remelted ingots are bright silver.
The original ingot had 40/1stamped in it

[Linstrum]

The yellow residue when cool is usually either antimony oxide or bismuth oxide. Antimony is a common ingredient in most lead alloys and babbit alloys, bismuth is a component of non toxic plumbing solders and low melting point alloys like are used for fire sprinklers and pressure cooker relief plugs. Cerro-Safe is a bismuth-tin alloy. Bismuth-tin alloys are easily confused with lead because of the same color when fresh. Bismuth-tin alloys do not tarnish while lead alloys do. Having 40/1 stamped on it is meaningless without having what metals are in the "40" and "1".

Don't throw that alloy out, if you get it identified as a bismuth-tin alloy it might be worth a bit, maybe $7 a pound. If it melts in boiling water it is definitely a bismuth alloy like Cerro-Safe.

rl 1,192

[lksmith]

What is the approximate hardness of such an alloy (cerrosafe)?
I tested it with my lee hardness testing kit and it is below 8BHN which is as low as my chart goes.
I compared it to the indention of a piece of lead that I know is 100% lead (hornady swaged round balls, and rotometal lead, both had identical impression sizes) and is only .001-.002 smaller than the lead indention

[Linstrum]

I haven't seen any specific Brinell hardness data for Cerrosafe, but it is too hard to scratch with your thumb nail, but not by much. At room temperature, when struck with a small hammer, Cerro-Safe will instantaneously melt and then re-freeze right where the hammer indentation is. You won't see a puddle of molten metal because it freezes nearly instantly after being struck, but you can see where the liquid metal squirts out from under the hammer. Wear eye protection because the metal shoots out at about 1000 feet per second and will penetrate your eyes and skin! It feels like a needle stab when the high velocity molten metal penetrates your skin, but I don't recommend hitting things with a hammer to see if molten metal will penetrate your body as a diagnostic test. Instead, putting a small amount of alloy in a tin can of boiling water to see if it melts is the best test since very few alloys melt at that low of a temperature.

rl 1,194