A method of manufacturing a ceramic filter having a controlled filter channel opening size, comprises fabricating a ceramic precursor element having a structure comprising first and second surfaces and an arrangement of flared pores extending between said first and second surfaces. An apex of a said flared pore is towards the first surface and a base of said flared pore is towards the second surface and is larger than the apex. The flared pore contains a polymer material, such as polyethersulphone and regions between the flared pores comprise ceramic material, such as aluminium oxide. The ceramic precursor element is sintered to fuse the ceramic material and remove said polymer material. A controlled thickness portion of the first surface is removed preferably by using a solvent or by scraping to open the flared pores to the controlled filter channel opening size. The ceramic filter is useful in membrane filtration for the industrial separation of blood cells to eliminate leukocytes.
