A cap for an investment vessel for receiving investment material comprises a platform having a contoured edge and an underside. A wedge is located on the underside of the platform and is frictionally engageable with at least a portion of an inner edge of the top of the vessel. When the cap is placed in frictional engagement with the vessel, the contoured edge provides a restricted opening to the vessel for controlling the flow of the investment material. A lip is provided on the platform at the contoured edge for channeling investment material to the opening.