Okay, I haven't been reading the gunzines and cast boolit manuals every year and old stuff to some here is kinda new to me.
References come and go here to heating up moulds on a hot plate to get them up to temp. The old stuff I remember said to NEVER apply high heat lest the iron blocks warp. And NEVER just dip the corner of a block into the melt to heat them up, same reason, might warp the blocks. The 70s vintage then-new Lee moulds touted their advantages as including just dipping the blocks in the melt, since their aluminum moulds won't warp.
So is the modern doctrine that it's okay to put lotsa heat on iron mould blocks? I see no other way to get them hot enough to melt lead smears (before wiping with burlap or brass wool and such), as some recommend doing in the "Lead Adhearing to Mould" thread.
Was messing with a single-cavity mould the other day and it sure would be nice to get 'em up to temp in less than 30 pours...