A tumbling container is mounted for rotation with a curved screen fixedly mounted within the tumbling container. A multiple vane paddle is mounted to a shaft that is rotatably mounted to the tumbling container. The paddle vanes are formed with angular edges. As the tumbler rotates and the paddle rotates, powder is repeatedly dropped onto the screen to be sifted with the aid of the paddle. Rotating the tumbler further drops unsifted portions of the powder from the screen to mix with additional powder in the tumbler body. Thus, sifting and blending of powders is accomplished in one single operation. The invention utilizes an apparatus having a multiple section screen and a multiple section paddle to enable assembly through the openings in the tumbling container. The screen of a second embodiment has a cowl adjacent to each screen opening to optimize powder lump disintegration.