[sagacious]

Originally Posted by kelly

You have changed my out look on fluxing. Thank you. Not to change the subject but how dos smoking the mold help. I am having trouble seeing a difference in my pour and do not any change.

Smoking the mold is good general practice, and good advice for anyone using metal molds. However, you're right-- in some cases it doesn't seem to make a noticeable difference. I always smoke a new mold, just in case.

Smoking the mold does several potentially critical (potentially very helpful) things:
First, it helps 'break in' a new mold. The surface of the cavities of an aluminum or steel mold may not be completely anodized, or coated with 'bluing' (steel mold), and the lead may tend to stick in the cavities until the mold has been used for a few times. The soot layer functions as a very good non-stick coating for the cavities.

2) The soot (carbon) layer is a thin insulating layer in the cavity. What that does is allow the lead to 'slosh and slide' into the cavities freely and fully for a fraction of a second before it starts to solidify. That's always good. It can be particularly helpful in getting a mold to fill out in a narrow collar area.

3) The soot layer helps prevent hollow areas or voids in larger molds, as it reduces the potential for the lead to freeze in the gate, or to freeze where it contacts the side of the mold cavity.

On some molds, such as smaller jig molds, or molds with tight tolerances, I'll smoke the entire face of the mold halves. Sometimes a speck of lead, or many specks will hold the mold open a tiny bit and cause flashing on the jighead. I'm sure that's happened to many of us. If the mold face is silver, it can be a real pain to track down and scrape off all the lead bits-- and they often stick really tight. If the mold face has been smoked, and bits of lead that get splashed on are instantly visible, and easily removed.

I'm sure there's other benefits that I haven't listed. Maybe someone will chime-in with their thoughts or experience.

I would think all the prep would be during the flux proses.

Well yes, but part of the prep is prepping the mold cavities (if necessary), pre-heating the mold, organizing your pouring space, preheating your hooks and forms (if necessary), etc. No doubt you do all that stuff without thinking about it any more, but there's a lot of folks new to lead pouring that haven't worked out all the kinks. Smoking the cavities is easy, and it will definitely help in many cases. There's enough frustration to be had in learning to pour lead, so every bit of prep that will save grief later is good general advice. I can recall a few people here on TU that replied they had better pours after smoking the cavities. So, you're right, it may not be important for you with your mold(s), but it's a good thing to keep in mind, and a good thing to do to head off potential problems.

One last thing A past post cadman having good pouring when cold out (close to sea level? no moiture in air). I am lucky to have alot of pouring like that and live in utah. Can altitude or lack of moisture in the air change the properties, change like boiling water at high altitude it needs to be hoter to boil.

I'm not sure, I haven't seen any data on elevation re lead pouring, and have no experience with pouring lead above 1000'. Could be, but my guess is there's probably little affect due specifically to altitude.

Humidity? Now that could just be a significant factor, as increased humidity can increase the amount of surface oxides formed, and so could adversely affect mold fill-out. Plumber's lead is 'pure' lead, and pure lead is more prone to develop a significant amount of surface oxide than hard lead-- so you may have something there! So, if you pour soft lead, high-humidity days may not give the best results. And, if you pour soft lead when humidity is high, flux the lead every now and then to keep the melt fluidity high and to remove the lead oxides-- so that you don't run into problems. Also, adding some ww lead to the soft lead when humidity is high is another option, as that will reduce surface oxide formation too. Lower humidity during wintertime sounds like it might make more than enough difference to offset the cold air (it's relatively low humidity all year where I pour).

Good questions, good stuff-- you guys may have gotten to the bottom of a frustrating phenomenon! Flux early, flux often is a good solution to many problems.