Woohoo first of all, just found you all and tickled pink!
Secondly, something I learned t'other day
Just wanted to mention something a knowledgable source told me the other day. I was buying a bunch of ingredients for my core and stove at a masonry place (in New England) and I was asking about perlite, why they only sold vermiculite. He said it isn't so much the product, it has it's applications, but when it comes to mixing it for masonry projects, adding perlite is more like adding marbles to a mix, essentially weakening the mixture due to a presence of an aggregate that doesn't bond. On the other hand, adding vermiculite to a mix is more along the lines of adding oatmeal, yes it absorbs water, but in that process also bonds with the mix! I found it invaluable info and was glad to be getting vermiculite, masonry grade of course.
Please don't get me wrong, perlite has its applications, but in a castable core thread I wanted to share information that I felt grateful to receive, in fact it was rather revelatory!
Now if I could just find some fire clay! I am swinging by a local potter tomorrow, I'd like to stretch all that furnace cement as well as splurging on a bag of nox-Crete, replete with stainless steel needles!
Hope this helps, make it rockety!