What sintered glass crucible made of?
Sintered glass is made from glass powders pressed at a temperature under the melting point of glass.
A sinterd funnel is simply a funnel with a built in filter. The filter is sintered, I think that this means that small particles are compressed together (and heated ?) to form a single piece of material with many small holes. The sintered funnels I use are made of glass, a link to some images is below (not mine). http://curlyarrow.blogspot.com/2008/01/how-to-clean-your-sintered-funnel.html I have also used sintered polyethylene and sintered stainless steel for filtering.
Sintered glass is a glass mesh used for filtration. It can be used instead of filter paper, and in fact is preferable to filter paper. Its other advantage is that it is permanent so you can get various different pieces of glassware with sintered glass in it e.g. an enclosed filter suitable for filtration under nitrogen. As for the porosity.... Porosity of sintered glass is labelled by integers from 0-5 (viz. 0, 1, 2, 3…
I'm not certain but I imagine it is a combinations of things... Sheffield has a great history of steel making, including 'crucible steel' that was made by heating and melting iron in a container called a crucible. Also, the theatre can be said to be a 'melting pot' of ideas and so likened to a crucible.