thomas rubino wrote:David; ; Components of cast cores & risers are one 50#sack fireclay + one 2 cubic foot bag perlite + fiberglass as a binder and as much refractory cement as you can afford , I used 2 gal tub between core & riser. I would have 4 bags of fireclay on hand and 2 four foot bags of perlite, I used bagged concrete fiberglass as my binder maybe 1/2 bag for core less for the riser. I used an 8" sonitube as my inner form on the riser with a 16 gal metal barrel as the outer form. The core is formed with plywood & hardy board. When i build my next cast core & riser I will also have a bottle of sodium silicate (waterglass) on hand and paint all fire surfaces inside the core & the top of the riser just before firing to create a harder refractory surface.