Method of making a blown plastic container having a multi-axially stretch oriented concave bottom

In a method of making a blown container of thermoplastic material from an axially elongated blowable preform, the container having a concave bottom, the steps of:

• enclosing the preform within the interior cavity of a blow mold, said mold cavity conforming to the shape of said container except for one open side closed by a removable first bottom wall having a substantially flat upper surface;
• blowing the preform interiorly of the mold cavity to the shape of the blown container with the exception of the concave bottom, that portion of the blown preform corresponding to the container bottom being blown against the substantially flat upper surface of said bottom mold wall, so that said portion is substantially planar;
• removing the first bottom mold wall to expose said substantially planar preform portion in alignment with the mold open side;
• closing the mold open side with a second and different reforming element having a convex upper surface exposed to said cavity;
• contacting the upper surface of said reforming element with said substantially planar portion of said preform, displacing said reforming element into the cavity with said convex surface thereof reforming said substantially planar preform portion into a concave bottom for said container, and chilling the concave bottom to its concave configuration.