The plaster-piece mold for this is done, waiting for the last section to set before taking it apart, and finishing up the last segment of a time-lapse video of it.
It took 125# of plaster and some 7 gallons of water, about half of that water will evaporate out.
It will be probably 2 weeks with fans blowing on it to dry it out enough to use for pressing the clay into.
This is exactly how the working molds were made for all of the Elmslie “Sullivaesque” terracotta, and all of the similar architectural terracotta as well.
About the biggest difference between then and now is only in my using a rubber positive copy instead of taking this plaster mold directly off the original clay model. With the rubber positive I could make additional or replacement molds from that whereas the clay original master is typically destroyed in the process.
Back in the old days these kinds of designs were typically custom made for each building job, so they tended to only need a few of each, a dozen maybe. If they made terracotta cornices and windowsills, these were typically made by extruding the clay thru a die under mechanical pressure for small ones, for larger ones they used a system of running a template along the clay which was the same way they did the elaborate plaster ceiling crown moldings- shaped in place using wood runner strips and templates.