[TheForge] Getting the lead out or the tar baby?

[Steve Bloom]

Greetings --

I wanted to pose a question to the smithing-mega-brain.  I'm building 
an 8-plate kabuto with a student.  The process involves over-dishing 
16-gauge mild steel pieces (8 of them - who would have thunk") and 
then planishing them onto a form (with lead hammers).  The form are 
surplus and slightly modified Army helmets (Italian are best - due to 
the shape but US units will do and are readily 
available).  Unfortunately. the steel in the helmets wasn't really 
intended to take repeated blows, so fracturing is just a matter of time.

I decided that a cooler way to do the work would be to thicken the 
rim (so a vast number of vise-grips can hold the pieces in place) and 
fill the form with something resilient to extend the life time of the 
form.  My candidates are lead and roofing tar (both available in my 
junk pile).  The volume for the form is about 3000 cc.

Lead is about 11.4 times the density of water, so that translates to 
75 lbs of lead.  The equivalent in tar is about 6 lbs (and also melts 
at a lower temp and has less health implications).  Soo....my 
question is "Will the tar stand up to the punishment or would the 
lead be better overall?"  It works in pitch bowls but as a form filler?

I would appreciate anyone with repousse and or armour dishing to chime in.

Thanks -- steve