Lead casting question

[norman horne, 12321]

Can someone tell me what is happening(metallurgically)when a bluish/purplish film forms on top of the melt. It is thick enough to be herded and scooped off. I cast at 850 degress. Thanks in advance.
Forgot to mention, I do flux frequently.

[Lou Lou Lou]

Accordingto the folks over on the Cast Boolit website, your temerature is too high. The Blue / Gold/ Purple is due to the heat. Lead melts at 600+ degrees. Above 1,000 degrees you can create big problems with vaporization (sic)

[ms3635v]

When casting, I make sure the molten lead stays bright silver...that way I know I'm at the right temperature. My bullets come out of the mold shiny and there aren't any wrinkles or voids. Started casting this way in 1975 and haven't changed since.

[Fauch125]

Is it a new mould? If so did you get all the oil off the mould before 1st use? I've had some discoloration occur due to left over oil on the mould. Now, i clean new moulds with simple green, smoke them with a candle as a release agent, then store the moulds full of lead to avoid reoiling, have not had the problem reoccur.

[Ron/The Old Reb]

First don't scoop it off. Lower your heat then flux the lead and stir it with something that will reach the the bottom of the pot. Then scoop off what is still floating on top. Flux it when ever it starts to reform. To keep from getting all the smoke when you flux it. I cut the heads off of wood safety matches and drop one in before I start to stir. Be sure to use a good heavy glove.

[Maillemaker]

I cast at 750F. You should cast at the lowest temperature that gives you good fill in your mold.

I find that no matter what the temperature, the top surface of the molten lead will oxidize over time. I let it. I figure this forms a protective barrier preventing the rest of the lead from oxidizing - if you scoop this off and expose fresh lead then that will also oxidize.

I'm working with a bottom-pour pot so it is no problem just to let a skin form on the top. I only skimm dross off after an initial melt. After that, I leave it be.

Steve