[Avodah] Are there any chemists on Avodah?

[Hankman]

Are there any chemists on Avodah? In the daf, 54a, the gemara brings a Tani Levi that describes the construction of the Misbeach. It was concrete-like in nature. It used forms much as we would today, aggregate of perfectly smooth stones (not to be felt when passing a fingernail over them) and some sort of matrix or "mortar" composed of some sort of mixture of sid, kunya and zefes, commonly translated as plaster or lime,  lead, and pitch or bitumen. My question is about this "mortar" they used. I did a bit of a search to see if anything turned up about such a combination - nothing did. There was some sort of use for lime and asphalt at http://www.lime.org/uses_of_lime/construction/asphalt.asp under
Adding Hydrated Lime to Hot Mix Asphalt,
but I doubt this relates to nidan didan. Can anyone explain how they used this mixture in forming the cement and how this functioned chemically? Do we have any modern equivalent? Part of what bothers me, is the high temperature (621.5 F) required to keep the lead molten? How to keep it from solidifying before being poured over such a large area in the neighborhood of 60 ft squared? Was it perhaps some chemical compound that included pb as a component (but without exhibiting a high melting point) and some of the resins extracted from the bitumen together with the lime?

Can anyone enlighten me?

BTW, I think there is a discussion about whether it is iron or metal that is under prohibition of use for the mizbeach. But apparently lead was OK as a component of the mizbeach? Perhaps the lead only enters the "mortar" as an unrecognizable component of a compound (if not just iron is under prohibition) with its own set of physical properties?

Also does the fingernail rule only apply to the individual stone aggregate, or to the entire surface after removal of the form. If so, the aggregate-mortar joints must have been near perfect - almost like a polished surface!? Also does this fingernail rule apply to stone aggregate buried in the interior of the mizbeach and never visible at its surface? If yes - you will never know whether during construction a stone in the interior became scratched and made the mizbeach pasul!

Kol Tuv

Chaim Manaster
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