The following link is to a good article on lead pot fluxing.

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As a metallurgical engineer I have a few comments.  Most of us use only lead and tin alloys so the need for fluxing (removing) metals such as copper, zinc, antimony, etc. is not very important.  What is important is to minimize the loss of tin.  Tin oxide along with lead oxide is the main component in the "scum" on a lead pot and this forms because of contact with air.  Sawdust as recommended in the Fryxell article reduces most of the oxides back into the lead-tin alloy, just what we want, but it is smokey and messy.  It also protects the lead bath from contact with air.

I don't use sawdust or wax or oils, I use crushed charcoal on the melt.  It should be lump charcoal because charcoal briquettes contain all sorts of crap like organic compounds with high sulfur plus they are full of ash.  I find the charcoal is easy to push aside when I fill the dipper.  It floats do it doesn't get into mold.   

Charcoal does form ash and I just skim this off every few hours and replace the charcoal.   BTW- I cast quite hot, 800 F using a PID controlled 50 pound lead pot and if I do my part the bullets are within +/- 0.2 gr.  the biggest remaining variable is the mold temperature.  I've got to work on that. 

By buying a great rifle, controlling bullet weight, using the best lube and weighing each powder charge to 0.1 gr I have proven that I'm just a lousy shot . 

Maybe practicing would help....

Dave

The sludge looks to me like what is left on top of the lead after the beeswax is burned off. You are fluxing way too much. Once when you alloy your tin and lead should be enough. Now that I’m lazy and buy my bullet alloy in bars I just melt it and cast.
By the way I also coat my ladle with mold prep.

40 Rod

Noticed when I flux with rodeo rosin, a lot of the dross goes away.
Chuck

shovel80 wrote on Aug 14^th, 2016 at 10:42am:


They DO smolder.  So I just set them half way out the roof window (above the lead pot) in the dormer.  Convection carries the smoke and lead-pot fumes out together!

Pentz wrote on Aug 14^th, 2016 at 9:07pm:


Seems to me that it builds up on top and then putting the ladle in and out to cast...it builds up on the ladel...sometimes I tap off some of it and skim it off...I use a stainless steel table spoon..

Terry

How does tinning occur?

As far as I can see, the RCBS dipper is the same cast iron material as the Lyman/Ideal, and picks up (as opposed to generating) the same level of dross that the earlier design does.  I have to turn both upside down and bang them on the top of the pot to shake the deposits out with the same frequency.

My old Organic Chem professor laid down this universal law:  "Whenever you melt anything, you decompose some of it."  Keeping it molten simply aggravates the problem.  If you left the molten alloy in the pot indefinitely, it would all oxidize to dross.

In my experience, the decomposition occurs at the inside surface of the pot, where the heat is maximum, and then rises to the surface as more dross is produced.  I flux at the beginning, and can usually cast the pot empty (except for .22s) without needing to do it again.  I periodically tap the dross out of the dipper, use it to push the accumulated crud away from where I fill it, and continue.

I've used about everything sold or recommended for flux, but my standard for casting is wax, because a lit candle drips controllably into the pot while I stir with the other hand, and I can set the smoke on fire with it when it gets too thick.  A good fluxing job with wax doesn't look like the picture; it's a brownish-black powder, typically, easy to skim off.  Sticking the extinguished candle wick into the pour spout will dislodge any dross that clings there.

Sawdust works the same way as wax, except the carbonized sawdust is skimmed off with the dirt.  I only use the resin chips and Marvelux for smelting very dirty metal;  they're better at picking up the crud, but the molten goo that results is harder to skim off.