Just sharing as I learn and experiment. I’m still new to casting and have only worked with cuttle bone and most recently in Tufa. Being the research fanatic that I am, I do my diligence in trying to apply all the “rules”, thinking it’ll all come out perfect…HA! So it’s been tufa casting weekend; the first one I carved was a ring shank. After carving I painted it with water glass (undiluted like syrup), added vents, sooted it up really good, made the pour and !@#$%&$#@! The pour was incomplete and apparently the the undiluted water glass also kept the fine texture of the tufa from showing up. It may have also been the reason for the incomplete pour? It also broke the mold as I was removing the casting.
So last night I carved up another one…no water glass this time at all. I also broke the rules by forgetting to carve in vents and I also ground the bottom of the tufa dangerously close to the carving on the bottom. So I made the pour anyway and…voila! Perfect! Thinking it was a fluke I poured two more this morning and they all came out perfect and lifted out without breaking the thin edge at the bottom. So what did I learn? I’ve got a lot of learning ahead and experimentation to do…and the “rules” ain’t necessarily so 
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Why don’t you take a look at Delft Clay casting…Rob
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They look fantastic! 
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