A component is treated in a fluidized bed by insertion of only a treatment part of the component into the treatment chamber of a fluidized bed apparatus. The non-treatment part of the component is located substantially outside the treatment chamber and out of contact with the fluidized bed. The boundary between the treatment part and the non-treatment part of the component is defined by a boundary containment surface at a fixed location with respect to the component. The boundary containment surface may be a seal which seals between the component to be treated and an aperture in a side wall of the treatment chamber.