c,

> what is the binding agent for "cast stone"?  what the hell is even in 
> cast stone? is it dolphin-safe?  is it just sand (which I guess is 
> long-ago stone) or do they crush up stone directly for the purpose?

Portland cement usually. And there are a number of variations of that 
material. Not heard yet of natural cement for it tho would not rule it 
out. Lime of any sort would not hold up. Also possibly modifiers, like 
latex or polymers. Cast stone generally has in it what you would find in 
concrete. Though with possibly a bit more selection of the specific 
coloration of aggregates, and usually in-organic tints. Instead of the 
usual gray limestone aggregate you might have marble chips, or almost 
any stone can be used as an aggregate. You could use crushed & graded 
pink granite. Yes, there is sand, that is an aggregate, and that also 
can be selected for size & color & shape. And often there is steel 
reinforcement which tends these days to be stainless steel.

Then there is GFRC which is Glass Fiber Reinforced Concrete. This is 
more-or-less the same mix as the above only with reinforcement of short 
(like 1/4" to 1/2" long) strands of glass fiber. With this the unit is 
essentially a hollow shell with a profile, it considerably reduces 
weight, and the thikness fo the shell can be like 3/4".

The game is to play with all of the variables of material & their 
interaction and to see if one can fake out a stone from it.

At previously mentioned Barnes & Noble at the very top of the building 
there are sunflowers... you have to see it to understand what I mean. 
The originals were in terra cotta. They are a pleasant pinkish orange. 
On that project a few were missing and we replaced them with cast 
concrete replicas... to do 2-3 units in terra cotta would have been cost 
prohibitive for the project as well as too long of a time for 
fabrication, let alone getting anyone interested to put them into 
production. Regardless, if you look up you can see brightly colored 
units and not so brightly slightly grayish units. Though if I did not 
point it out you would never think to know. It is a good distance from 
the ground to the top of the building. Though the cast units lacked a 
shine, they were a bit dull when set next to the dirty originals... when 
they were first installed they were a much closer match in color than 
they are now.

There are associations related with these products and there are studies 
of a scientific nature as well as a host of specifications. Cast stone 
is used for things like drainage pipe, tunnel pipe, septic tanks, garden 
statuary, landscape furniture, pre-cast building units etc. and the 
application to replication of architectural stone is a subset of a much 
larger industry. It is similar as if we were to get into a discussion 
regarding the replication of historic duct tape.

> i would like to take two blocks, make one into cast stone and lay it 
> next to the other, then wait for 500 years.

There are examples around of interesting older concrete. You may go look 
for what Edison did in concrete regarding precast houses. And it you go 
across the water you may actually find that 500 year old example sitting 
out waiting for your appreciation.

>  maybe we are just not using cast stone effectively, maybe it has its 
> own aesthetic.

It does. If an architect were so inclined they could design something 
interesting in cast stone. I am reminded tho of monumental structures, 
such as fountains and statuary, made with cast stone that has weathered 
and distressed... though I like the distressed effects the aesthetic is 
not one that most patrons of a public park appreciate.

][<

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