Pottery and Porcelain without bottom

And sorry but I need to understand why some pottery / porcelain pieces are without a base. Some of these are old, some more modern.

Any ideas on these?

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All of your examples look like they are made by a process called "slip casting". This method uses molds, with 2 or more pieces, made of an absorbent material such as plaster. A slurry of wet clay is poured in to fill the mold, and it is allowed to stand for awhile. Moisture is absorbed through the mold, and a thin layer of stiff clay forms on the interior. When the clay reaches the desired thickness the remainder of the slip is poured back out. The hole in the base is for pouring the slip in and out. Depending on how the mold is designed, there may be more or less of a base left on the piece. In addition to the large holes in the base, slip cast figures will typically be relatively thin, and the interior surface will closely follow the exterior form.

After the mold is removed, the figure would be allowed to air dry and then would be fired and decorated.

This method would be distinguished from press molding. In this technique, "bats" of moist clay were pressed by hand into open molds and allowed to set. The clay pieces would then be joined using slip, after which the form would be fired and decorated. Press molded figures will not show large holes, but may have much smaller holes to allow for hot gases to escape during the firing.

 

Brill - Thanks so much for time on this, really enlightening